U. S. DEPARTMENT OF THE INTERIOR U. S. GEOLOGICAL SURVEY Dense Three-Dimensional Array near Garni, Armenia as Part of the Joint Eurasian Seismic Studies Program (Objectives, Array Design, Archived Data, and Preliminary Wave-Slowness Analysis) edited by Gary Glassmoyer and Roger D. Borcherdt OPEN-FILE REPORT 93-216 This report is preliminary and has not been reviewed for conformity with U. S. Geological Survey editorial standards. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U. S. Government. Menlo Park, California February 1993 Dense Three-Dimensional Array near Garni, Armenia as Part of the Joint Eurasian Seismic Studies Program (Objectives, Array Design, Archived Data, and Preliminary Wave-Slowness Analysis) CONTENTS Page Chapter Title 1 I Summary and Objectives for a Dense Three-Dimensional Array near Garni, Armenia 4 II Site Selection, Array Design, and Recording Instrumentation for the Dense Three-Dimensional Array near Garni, Armenia 17 III Digital GEOS Data from Garni, Armenia as Archived on Optical Disk 47 Plots of GEOS records for events at five or more sensor locations from 26 June 1990 through 10 August 1992 334 IV A PC-Based Seismic System for Armenia 338 Plots of PC-XDETECT records from 21 September 1990 through 01 January 1991 416 V Near-Surface Measurements of P- and S-Wave Velocities from the Dense Three-Dimensional Array near Garni, Armenia 433 Wave-slowness contour plots for selected events 450 REFERENCES CHAPTER I Summary and Objectives for a Dense Three-Dimensional Array near Garni, Armenia J. Filson, R. D. Borcherdt, W. H. K. Lee, E. Cranswick, C. Dietel, E. Sembera, J. Mori, and J. Sena (U. S. Geological Survey) L. Hakhverdian, R. Amirbekian, V. Aharonian, K. Safarian, H. Galagian, and G. Apoian (Yerevan Seismic Station) R. Banfill (Small Systems Support, Big Water, Utah) Introduction Within two weeks following a major earthquake in December 1988 a team of seismologists and engineers from the United States went to Armenia to investigate the cause and effects of that tragic event. A modest but sustained cooperative effort between seismologists in Armenia and in the U. S. Geological Survey (USGS) has grown from that initial post-earthquake investigation. In 1989 the USGS began to participate in what is now called the Joint Seismic Program (JSP) between the United States and what was then the Union of Soviet Socialist Republics (USSR). This program is led on the U. S. side by the Incorporated Research Institutions for Seismology (IRIS) and on the Soviet side by the Institute of Physics of the Earth. In 1989 the Soviet side suggested that among other things the JSP project should include detailed studies of the seismicity of certain earthquake-prone areas of the Soviet Union. Kirgizia and Armenia were offered as places where arrays of seismometers could be installed for this purpose. As a participant in theJSP and as the organizer of the post-earthquake investigation in Armenia, the USGS was chosen to take up the array work in Armenia. Objectives During the 1988 post-earthquake investigation Armenian colleagues suggested that a portable seismic station be installed at a geophysical observatory near Garni, about 20 km east of the capital, Yerevan (Figure 2-3). A trip to this site revealed a two-story building with a horizontal tunnel, or adit, running from the basement about 200 meters into the hill behind the building. This tunnel had been constructed for the purpose of obtaining geophysical observations relevant to earthquake prediction. The tunnel was lined with concrete and had several small rooms with piers suitable for seismic recording (Figure 2-5). The tunnel is described in more detail in the next chapter. Given this excellent facility and the charge from the Joint Seismic Program, a USGS team went to Armenia in June 1990 with the purpose of installing a dense seismometer array in and around this tunnel. Other than taking advantage of an exceptional site, the scientific justification for the array can be seen in Figure 2-4. The Garni site lies on the northern edge of a long, steep valley that runs northeast-southwest opening to the southwest onto the larger and broader valley of the Araks River about 10 km south of Yerevan. There is concern that the topography of the narrow valley near Garni is controlled by an active fault. A Roman temple at Garni was destroyed by a "great" earthquake in 1679. If the valley follows the course of an active fault, then this fault represents a considerable hazard to Yerevan, a city of 1.2 million people, with construction of the type that was destroyed in Spitak and Leninakan in 1988 killing over 25,000 people. The purpose of the array is to detect and locate if possible any local seismicity associated with a larger pattern of strain release along this fault. Of course a wider microearthquake network would have been more suitable for this task, but was not considered possible given the time allowed and the funds provided. The recording scheme is built around the General Earthquake Observtion Systems (GEOS) developed and described by Borcherdt et. al. (1985). A PC-based system developed by W. H. K. Lee is also used for recording-backup and display of the data. The seismometers used are 1 Hz Mark Products L-4Cs deployed in three-component sets. The fact that the tunnel is set into a hill provided the opportunity to establish sites on the hill above the tunnel and thus provide a three dimensional array geometry. The GEOS and PC recorders were set up in the observatory building with cable connections to the seismometer sites. The total aperture of the array is less than 1 km. More detailed descriptions of the array geometry and recording system specifications are given in the next chapter. (The array deployment was completed within a two-week period during June 1990. Anyone who has ever participated in a similar exercise in a foreign country will appreciate the difficulties endured and the problems that had to be met and overcome. A full description of the effort will probably be wasted on anyone who has not. However, it must be said that the task could not have been completed without the help of Armenian colleagues and their families. We slept in an abandoned dormitory with no running water or other facilities. Our food was bought, cooked, and served by the wives and friends of the Armenians working with us on the project. Our Armenian colleagues carried gear, dug pits, pulled cable, mixed concrete, and generally shared in all of the labor intensive activities.) Summary Since the installation of the dense array nearly one thousand events have been recorded at one or more of the array sites. The array has operated since July 1990 with some gaps in recording caused by strains on the infrastructure of Armenia due to the breakup of the Soviet Union and military actions resulting from disputes with Azerbaijan over contested territory. This report documents the recordings of the array and shows examples of the types of events that are available for study. Data from the array has been placed on optical disks and is available on these disks from the USGS and also through the IRIS Data Management Center in Seattle, Washington. Data from the array has proven amenable to three-dimensional analysis as described in Chapter V. The analysis of the local seismicity is not yet complete. It is clear that there is considerable local activity, occurring at times of day random enough that it cannot be due to blasting. Accurate location of these events with an array this small remains a problem of study. CHAPTER II Site Selection, Array Design, and Recording Instrumentation for the Dense Three-Dimensional Array near Garni, Armenia R. D. Borcherdt, J. Filson, W. H. K. Lee, E. Cranswick, C. Dietel, G. Glassmoyer, E. Sembera, and J. Mori (U. S. Geological Survey) L. Hakhverdian, R. Amirbekian, V. Aharonian, K. Safarian, H. Galagian, and G. Apoian (Yerevan Seismic Station) R. Banfill (Small Systems Support, Big Water, Utah) SUMMARY Scientific objectives and logistic constraints were primary considerations in site selection and design of the dense three-dimensional array near Garni, Armenia. Principle scientific objectives concerned the need for high-frequency discrimination studies and the need to monitor seismicity for improved seismic hazard analyses for the capitol city of Yerevan with a population of 1.2 million. Principle logistic constraints concerned availability of supplies, fuel, transportation resources and site security. Instrumentation selection was based on availability of resources, familiarity, and reliability. SITE SELECTION The site selected for array installation was developed for geophysical monitoring purposes in the 1970s as a cooperative effort involving the USSR and Armenian Academies of Science. The facility is known as the Garni Observatory. Logistic difficulties concerned with availability of transportation vehicles and fuel were considered sufficient to preclude establishment of isolated multiple monitoring stations that might require regular visits for power maintenance. Garni is located approximately 20 kilometers east of the capitol city of Yerevan in a moderately remote region. The location relative to other landmarks is shown at different map scales in Figures 2-1, 2-2, 2-3 and 2-4. The observatory site is located at the base of a large hill which in turn forms the boundary for a small valley used for minor agricultural farming. The area near the observatory is used primarily for the grazing of a small dairy herd. The site consists of an elaborate two-dimensional horizontal tunnel complex (Figure 2-5) leading from the basement of the two-story observatory building (Figure 2-7), and about four hectares of property. The site is under the jurisdiction of local cooperating scientific officials and is relatively secure from vandalism. The extensive two-dimensional tunnel configuration at the observatory provided a unique opportunity to establish an array to serve as both a three-dimensional array for high-frequency discrimination studies and as an array to assist in monitoring seismicity for improved seismic hazard analyses for Yerevan. Seismic studies conducted at this site as part of the joint U. S. - U. S. S. R. cooperative studies following the devastating earthquakes of December 7, 1988 (Borcherdt et al., 1989), showed that the site is relatively well isolated from local cultural noise sources. ARRAY DESIGN The array design was developed to incorporate the two-dimensional configuration of the tunnel as shown in Figure 2-5. Using the length of the shortest arm of the tunnel as the minimum dimension of the array (~60 m), the array was designed within geometric constraints of the tunnel and available cable to resemble a nested tripartite configuration. The array is centered on a tetrahedron, consisting of sites G1A, G1B, G2B and G4A, with minimum distances between sensors being roughly 60 meters. Three-component sensors are located in a nested configuration with spacings of about 60, 120, 200, and 480 meters. The final vertical and horizontal apertures of the array are 87 and 823 meters, respectively. The final configuration of the array as defined by the locations of the three-component sensors is shown in Figure 2-6. To increase the aperture of the array the initial design included an additional three sites located at distances of about 1.5 km from the center of the array. The lack of appropriate housing in the area and scarcity of available resources led to the establishment of sites G6A and G7A. The first subsequent revisit of the site a few months later showed that continued maintenance of sites G6A and G7A was also an extreme imposition on local resources. As a result these stations were withdrawn from the array. INSTRUMENTATION Sensors _ Three single-component velocity transducers (1 Hz, Mark Products L-4C) oriented vertical, north-south, and east-west (refer to Table 2-1 for actual sensor orientations and positions) were emplaced at each of the array nodes indicated in Figure 2-6. Each of the sensors was emplaced on a concrete pad (~ 0.5 x 0.8 x 0.1 m) prepared at each site with leveling platforms and housings (Figures 2-9 and 2-10) according to specifications used for emplacement of sensors in the Central California Network. Sensor signals were transmitted over cables to a central recording area located in a secure room (Figure 2-8) on the second floor of the observatory building (Figure 2-7). It was necessary to use locally available unshielded cable for location G4B, because one large reel of shielded U. S. supplied cable was lost in shipping. Recording Instrumentation _ Array recording capabilities were designed to permit on-site data playback and analysis capability by local scientists and technicians. They were designed to provide redundancy in recording, playback, and event-timing capabilities. IBM compatible personal computers (PCs) were selected because of their wide availability and the local inaccessibility to other types of computer hardware. Subsequent array operation confirmed this conclusion and showed that even the replacement of common components such as hard disks was beyond the capacity of local resources. The array was designed so that seismic-event signals are recorded simultaneously at 200 samples per second (sps) both in 16-bit digital format using GEOS and in 12-bit digital format using a PC. Two sets of three-component signals are recorded on each six-channel GEOS recorder. In addition, each set of six analog sensor signals upon being amplified and filtered for anti-aliasing by GEOS is multiplexed and recorded on the PC. Detailed performance specifications of the GEOS and the personal computer system are provided by Borcherdt et al. (1985), and Lee et al. (1988), respectively. Timing _ Timing for the array was also designed to include redundancy. A master Omega receiver was used to establish absolute time for a master clock. In order to optimize relative timing each GEOS in the Garni Observatory was linked so as to synchronize and determine clock skew measurements with respect to the time pulse of the same master clock. The GEOS permits the clock skew measurements to be written to tape at operator selected time intervals. As an additional constraint to improve relative accuracy, the array was designed such that all signals for each event were digitized by a single analog-to-digital converter and recorded on the PC. In addition, special Omega receiver boards were designed that would have permited each GEOS to independently synchronize to Omega. Nominal GEOS clock drift rates are less than 80 milliseconds per day. Power _ To accommodate frequent power outages and variations in voltage levels, power was supplied through an uninterrupted power supply to the PC and through batteries for the GEOS. Ungrounded power lines in the Observatory required that special provisions be implemented to minimize electronic noise pick-up on signal cables. Electronic noise was a special problem for location G4B connected via unshielded cable and was most apparent at night, when electrical lights were being used. Power outages proved to be sufficiently severe so as to eventually damage PC hard disks and reduce on-site playback capabilities. Data Playback _ To facilitate on-site data playback, GEOS hardware and software capabilities were augmented to permit data playback via PC. Capabilities were developed for the simultaneous archival of both GEOS and PC data using two PCs networked via LANtastic. One PC is used as a data acquisition system and the other as a data playback, archival, and analysis system. Software was developed for automatic data archival using a simple multi-tasking environment. PC-compatible optical disks were selected as the medium for data archival. Previously developed GEOS playback software (RDGEOS) used on Digital Electronic Corporation mini-computers was converted for operation on PCs (PCGEOS). GEOS software was developed to permit each GEOS unit to serve as a field playback unit via RS-232 into the portable field PCs. Table 2-1. Sensor Locations and Orientations Station Relative Position Component Orientation (meters from tunnel door) (degrees clockwise from north) North East Down 5 ("N") 6 ("E") G1A 185.3 8.1 -0.7 2 92 G1B 180.0 53.0 -0.7 2 92 G2A 56.6 3.9 -0.1 2 92 G2B 125.1 -2.1 -0.7 2 92 G3A 4.8 0.9 0.0 2 92 G3B 100.4 1.4 -39.4 5 95 G4A 185.3 8.1 -60.5 5 95 G4B 384.5 16.7 -87.8 5 95 G5A -37.0 -189.8 13.5 5 95 G5B -63.7 167.0 -0.8 5 95 G6A -332.7 -386.6 31.0 5 95 G7A -159.5 344.7 12.1 5 95 Positions were determined assuming the tunnel is aligned 2.5 degrees east of north. Tunnel sensors were aligned with the tunnel axis. Surface sensors were aligned with magnetic north. Component 4 ("Vertical") is oriented with positive up. Location and orientation information was not recorded for preliminary stations GAA, GAB, GBA, GCA, GCB, GDA or GDB. CHAPTER III Digital GEOS Data from Garni, Armenia as Archived on Optical Disk G. Glassmoyer (U. S. Geological Survey) Processing As of this writing 245 GEOS tape cartridges from the Garni Array, representing the time period 26 June 1990 through 10 August 1992, have been played back at the National Strong Motion Data Center. The playback procedure involves demultiplexing of the data on tape cartridge using the computer programs RDGEOS on a DEC VAX computer or PCGEOS on an IBM-compatible PC. These programs write separate time-series files to disk for each channel recorded on GEOS, plus a time-stamp file that contains the start times of each (0.42 second) block of data recorded on the GEOS. Format The format used for the digital data is a block-binary file consisting of two header blocks (512 bytes each), one 2-byte integer, the other 4-byte real, followed by the data as 2-byte integers. Integer and real values are stored in the format used by DEC PDP and VAX computers. 2-byte integer values are stored as low-byte-first, high-byte-second signed integers in two's-complement form. 4-byte real values are stored as high-word-first, low-word-second. The integers are in the same format as used by PCs, however the real values are not the same format as PC real values. Programs RECSEC or VECTOR, written by E. Cranswick and R. Banfill, can be used to read the data on a PC. Filenames on the VAX are constructed from the station name and the start-of-record time. Characters 1-3 are the day-of-year (001-366), characters 4-5 the hour (00-23), characters 6-7 the minute (00-59), and character 8 represents the second (A-T, where A=0-2, B=3-5, ..., T=57-59). Character 9 is the component (4 is vertical, 5 and 6 are horizontal). The suffix is the station name. On the PC and the optical disk one less character is available for the filename so the hour is represented by a letter from A to X. Fixes Normally the GEOS can be relied upon to write to tape cartridge the complete recording sufficiently well to be read and accurately interpreted by the demultiplexing programs. It has been a recognized phenomenon that the GEOS instruments may occasionally fail in part or whole to write an accurate tape. These types of failures occurred in several forms in this study. In the case of data that can still be read by the programs, these failures can be grouped into two types: bit errors and block errors. An exact correction can usually be made for bit errors. These are what are often referred to as "glitches." The symptom is an occasional data value that is a large power of two different from the preceding and subsequent data values. The cause typically is memory board failures, but can also be in the analog-to-digital circuit. The computer program BITFIX is used to find and correct bit errors whenever the bit errors are sufficiently large compared to the true rate of change between data values. Block errors usually cannot be fully corrected. These are instances where the data block to be written to GEOS tape cartridge either is not written, or that which is written is corrupt. During playback the demultiplexing program (RDGEOS or PCGEOS) attempts to identify missing data blocks by examining the data-block time stamps. When these are identified, the null data value (integer header offset 3 of Table 3-1a) is written to the data file in place of the missing data. The G5 recordings have several instances of these data gaps. If the first data block of an event is corrupt, then the files created for that event will initially be given a name that does not indicate the true time of that event. Such files may also contain initial meaningless data. Such files are easily recognized by the program CHKTIME which compares the start-of-block time stamps, as written to the time-stamp files, to their expected time values. Start-of-record times have been corrected for these files using the program CHGTIME. In addition to allowing files to be given the correct start times, the program CHKTIME, reading the time-stamp files, also verifies the integrity of timing within the recordings. By this means several recordings have been found to have faulty internal timing. The cause of these failings is not always certain, but often is the result of reading a corrupt data block in the midst of an event. Recordings that contain internal timing errors have been corrected to the degree possible by using null values to mark those samples where no data are available, or by removing extra null values that the demultiplexing programs may have mistakenly added. These corrections are made using the editing capability of the programs RAWRI2 and RAWWI2. Recording parameters are stored in the two header blocks described in Table 3-1. The most critical values are shown in boldface. Many of these such as amplifier gain (see log-files in Figure 3-1) are derived from the GEOS cartridge. Other parameters such as station location or sensor orientation are added from the parameter list file GARNI.AHC. While usually accurate, there are instances where the polarity may be opposite from that which is indicated for vertical components. A careful evaluation of each clock correction in the manner described in the log-file section later should be made if these are important to a study. Plots of selected events Plots are included for those seismic events that were recorded at five or more three-component stations. These events are listed in Table 3-2, where the second-code of the filename is used to indicate those stations that recorded an event. The plots have been prepared using E. Cranswick's RECSEC program. They show each trace at equal amplitude, bundled by three-component station, for a duration proportional to the number of stations recording the event (5 seconds per station). The time (nominally UTC) of the first sample in each plot is indicated in large numbers on the right-hand side of the plot page. This is given as year (less 1900), day-of-year, hour, minute, second, and millisecond. The time scale at the top of the plot page is in seconds. Indicators on the right-hand side identify the individual trace. For example, G5B.V2 is station G5B's 2nd velocity channel - the first channel is up, the second is nominally north, and the third is nominally east. See Table 2-1 for actual horizontal orientations indicated for components 5 (=.V2) and 6 (=.V3). Numbers on the left-hand side of each trace indicate the maximum absolute value in digital counts through the end of the plotted portion of each trace (32767 is full-scale). Organization of optical disk Two IBM-3363 write-once-read-many (WORM) optical disks have been prepared containing calibration records and seismic triggers as listed in Table 3-3. One disk contains the 1990 data and the other contains the data from 1991 through 10 August 1992. Data are organized into subdirectories by day-of-year of event. These subdirectories are within parent directories by year. Log-files created by the demultiplexing programs from each tape are included in the LOG directory on the 1991-1992 disk. Also included are ORDARR files for use by the Cranswick and Banfill (WFPS) processing programs for each year. The WHERE list of Table 3-3 is also provided as text files for each year. Seismic triggers were selected by visual inspection and may still include such events as aircraft triggers or other signals that appear as possibly of seismic origin. Log-files Four examples of log-files are provided in Figures 3-1a through 3-1d. These show most of the useful types of information that can be read from a log-file. LOG28.G3 (Figure 3-1a) is a typical log-file from the program RDGEOS. The first line indicates the date and time the program was run and the program name and version. The log-file number (28) is added after the RDGEOS program has completed its operation, so it does not appear on this line which shows simply LOG.G3. Following is the channel/component naming description. The default refers to the log file itself as well as to the time-stamp files. Channel 1 data is component 4 of data for G3A, etc. The next lines indicate the tape/experiment number, location number, GEOS unit serial number, and the year. If any of these parameters change during the tape, such as the year, a new indication is made. In the next line file numbers include all files be they data or clock files as counted by the demultiplexing program (RDGEOS). The event numbers (Evt) are data files as counted by the GEOS. The type can be a trigger, continuous record, manual record, sensor calibration, amplifier calibration, or a clock file. Clock files can be master-clock synchronization (synch), manual synch, WWVB synch, WWVB synch failures (VB Synch TMO), or WWVB corrections. The time indicated for data files is of the first sample, as measured by the internal GEOS clock and is shown as day-of-year, hour, minute, second, and millisecond. The time standard can be none, manual, WWVB, or external. For the Garni data the time standard shown in this column is probably not reliable. An indication of none means that the clock has not been set and shows the elapsed time since the GEOS was turned on (starting day 001). Manual (MAN.) would indicate an operator set the clock by hand, such as by reading the time off of a watch. WWVB would indicate the clock was set by interpreting a WWVB time code. External (EXT.) is the only time standard that properly should have been used in this data set, and indicates that the internal GEOS clock was set by an external clock. The clock correction (Corr) as it is stored in the data files is shown in seconds that should be subtracted from the internal GEOS time to get the corrected time. See the later clock-correction example for a more complete discussion. DR100 name is a generic representation of the the names of the data files as they would be stored on a VAX. Duration is an estimate of the length of the recording in minutes and seconds. Srate is the sampling rate in samples per second. Pre-event is the length of time in seconds of GEOS blocks that were filled before the active block of the tape turn-on decision. Volts is the recorder battery voltage at the time of a trigger. The last four columns refer to parameters of the trigger algorithm. Trg ch is the trigger channel. STA is the short-term-average interval in seconds. LTA is the effective length of the long-term-average interval in seconds. Ratio is the threshold triggering level by which the short-term-average must exceed the long-term-average in order to trigger. Ratio is expressed in Fortran notation of 2 raised to a power. Motion type, amplifier gain, and anti-aliasing filter frequency are shown for each channel. Examples File 1 of G3 tape number 28 is a sensor calibration. It was recorded on GEOS unit number 5 beginning in the year 1991, day-of-year 121, hour 14, minute 47, second 27.382 according to the internal GEOS clock that was set by a master-clock. The clock correction stored for this record is 0.000 seconds. Channel 1 is ground-motion velocity recorded with 54 "decibels" (more accurately 2**(54/6) = 512 x ) gain using a 7-pole, 50-hertz anti-aliasing filter, and given the filename 1211447J4.G3A (121O47J4.G3A on the PC optical disk). It was sampled at 1200 samples per second and is a little less than 37 seconds long. Battery voltage is not reported for calibrations. File 2 is an amplifier calibration. The notation about 506 null values refers to this file; in ampliflier calibrations, however, it is due to a minor bug in the GEOS, and the data is complete without the nulls which have since been removed. In other data files each 506 null values represent a lost data block with the data value of -32768 being used in the place of the lost samples. File 7 is a triggered event. The GEOS was set to trigger by comparing for channel 1 the short-term-average of 0.4 seconds data to 8 (= 2**3) times the long-term-average representing 20 seconds of data. The batteries providing power to the GEOS were at 26.66 volts. Optimum battery voltage is about 24 to 28 volts. File 3 is a failure to read a WWVB time code. It should not have been set to try since no WWVB-encoded time-code was available. File 4 is the all-important clock correction! Eight attempts are made by the GEOS to read the one-second pulse of an external signal. This need not be a WWVB signal. As measured by the internal GEOS clock these pulses were detected 1, 0, 0, 0, 1, 0, 0, and 0 milliseconds after the second so the internal and external clocks are in near-perfect agreement. File 13 is also a clock correction. At its time the internal GEOS clock is 4 milliseconds fast relative to the external clock. For data files that follow the clock correction is recorded in the header as 0.004 seconds. Clock-Correction Example File 9 is a triggered recording of a magnitude 5.1 aftershock of the Ratchi, Georgia Earthquake. To get the best estimate of a clock correction for this event it is necessary to interpolate between two clock corrections. Using 0.25 milliseconds (the mean of the eight clock-correction measurements) from file 4 (121:14:56:44) and 4.00 milliseconds from file 13 (122:02:57:52) one can get by linear interpolation 3.5 milliseconds as a clock correction at 122:01:26:00. This 3.5 milliseconds would be subtracted from the 122:01:26:00.618 start-of-record time to get the external clock referenced time of 122:01:26:00.6145. When similar calculations are made for units G1, G2 and G4 their clock corrections are found to be -0.7, -7.0, and 16.2 milliseconds, respectively, and their externally referenced start-of-record times are ...:01.8837, ...:01.0980, and ...:01.5068. All units are using the same external clock signal, a master clock, so relative times have thus been determined. The absolute time could then also be determined since there is data in Table 3-4 indicating when the master clock was set to Omega-time. The master clock appears to have been synched to Omega sometime between 116:09:13 and 116:21:14. Later it was found to need adjusting by -5 milliseconds sometime between 125:23:47 and 126:08:05. The minimum estimate of drift for the master clock may be made by assuming the master clock was synched at 116:21:14 and was found to need an adjustment of -4.5 milliseconds at 126:08:05. The maximum estimate of drift for the master clock may be made by assuming the master clock was synched at 116:09:13 and was found to need an adjustment of -5.5 milliseconds at 125:23:47. This yields a range of -2.5 to -3.2 milliseconds, averaging to -2.8 milliseconds. This master-clock correction should be added to the previously calculated relative clock corrections to get absolute clock corrections. Thus respectively for G1, G2, G3 and G4 the best absolute clock corrections would be -0.0035, -0.0098, 0.0007 and 0.0134 seconds to be subtracted from GEOS start-of-record times. These are different from the values -0.002, -0.006, 0.000 and 0.011 seconds that are stored by default in the headers. All clock corrections stored on the optical disks are the inaccurate default values. The destinctions are small in this case but may approach one full second during intervals when clock synchs are infrequent. Under ideal circumstances, such as in this example, relative clock corrections could at best be accurate to 1 to 2 milliseconds and absolute clock corrections to 2 to 4 milliseconds. During the Spring of 1991 clock corrections were usually well recorded on all GEOSs. At other times, however, at least one recorder may have been misprogrammed, permitting only partial recovery of relative times. Also, the recording of master-clock resynchs (Table 3-4) was inconsistant, thus limiting the opportunities for the recovery of absolute time. Other Examples Following file 14 is a page break. At the end of the log-file is the line indicating the number of files processed. LOG03.G1 (Figure 3-1b) is a short example from the PCGEOS program, version 04.07. The first 2 files on this tape are corrupted clock files. The first 6 words (cells) stored in each block are the start time for that block. PCGEOS attempted to search ahead in the files for intact time information, but found none, so these files were skipped. The first file from this tape was corrupted. PCGEOS used default header information from file G1.GHD in the "grand-parent" directory for the file(s) it encountered before finding the readable header information in file 4 of this tape. The default header information uses serial number 99 and voltage equal to 20.00 as flags that the header information did not come from the tape. File 5 is a master-clock synch. At 183:08:26 the GEOS internal clock was set to match the external clock. The remaining information on this line is not reliable. LOG22.G1 (Figure 3-1c) begins with a master-clock synch, shows a faulty serial number and indicates an operator-initiated (continuous) recording. LOG06.G2 (Figure 3-1d) begins with clock information extracted from the header of the first trigger. PCGEOS will use this information, which is from the last clock correction on the previous tape, as a starting point for the default value of the clock correction. There is a risk that this value can be very out-of-date and inaccurate (as it may be here). The other examples did not have this either because they were from RDGEOS, had a corrupted header, or began with a clock file. Not shown is an example which ends with Physical End of Tape indicating that the tape was read all the way through instead of just to the end-of-tape mark. This would be the case for 100% full tapes. Known events 153 of the included events have been identified in the National Earthquake Information Center (NEIC) catalog. These are listed in Table 3-5 by date, Table 3-6 by distance, and Table 3-7 by magnitude. Body-wave magnitudes are used unless otherwise indicated. A travel-time plot of the larger events is shown in Figure 3-2. Table 3-1a. GEOS Header Descriptions (2-Byte Integer). Offset Description (Units) Value as Used in this Report 1 Number of extra integer header records (record size=512 bytes) 0 2 Number of ASCII header records 0 3 'Undefined' integer value [INULL] -32768 4 Data type (positive=real, negative=integer, absolute value=number of bytes per sample) -2 5 If =1 then (*) parameters are defined 1 10 Event year 11 Event day of year 12 Hour of event 13 Minute of event 14 Second of event 15 Millisecond of event 16 Microsecond of event 0 17 Sample number of first tickmark unused 18 Detection amplitude of tickmark unused 19 Number of tickmarks detected unused 20 Serial number of recording unit 21 Event sequence number 27 First active channel number recorded on unit 28 Actual channel number as recorded on unit 29 Total number of channels recorded on unit 30 Total number of components recorded for station I.D. 3 31 Number of data records that follow 32 Index of last sample in last record 33 Record size (bytes) 512 34 Playback program (1=RDGeos, 2=AfTape, 3=ANZA, 4=PCGEOS, 5=CrTape) 35 Playback program version number 36 Playback program 'sub-version' number 37 Recorder type (1=GEOS, 2=DR100, 3=Reftek 72-04, 4=Tustin A/D, 5=Synthetic) 1 38 Recorder version number 1 39 Recorder 'sub-version' number (GEOS software number) uncertain 40 Sensor unit serial number unreported 41 (*) Vertical orientation (degrees from up) 42 (*) Horizontal orientation (degrees clockwise from north) 43-49 [ASCII] Sensor model (7A2) unused 50 Location number 51 Experiment number (tape number) 52 Trigger algorithm type (1=STA/LTA) 53 Trigger STA (tenths of seconds) 54 Trigger LTA (seconds) 55 Trigger ratio STA/LTA (power of two) 56 Trigger component number 57 Pre-event memory size (tenths of seconds) 58 Post-trigger duration (seconds) unreported 101 (*) Bugger processing history unused 208 Directory number (study I.D. number) unused 209 Sub-directory number (tape-set number) unused 210-216 [ASCII] Filename (7A2) 217-219 [ASCII] Study name (3A2) unused 252 GEOS clock type (0=None, 1=WWVB, 2=External(master), 3=Manual) 253 GEOS event type (0=Continuous, 1=Trigger, 2=Preset, 3=Calibration, 4=Amplifier calibration, 5=Sensor calibration) 254 Motion unit (1=Acceleration in cm/s2, 2=Velocity in cm/s, 3=Displacement in cm, 50=Volumetric micro-strain) 2 255 Component number (1-3:acceleration, 4-6:velocity, 7-9:displacement; 1,4,7:vertical) 256 Number of samples in event (only valid when I031 < 128) Table 3-1b. GEOS Header Descriptions (4-Byte Real). Offset Description (Units) Value as Used in this Report 1 Number of extra real header records 0. 2 'Undefined' real value [RNULL] 1.7E38 5 Sample rate (samples per second) 200. 6 (*) Component sample lag (seconds) 39 (*) [ASCII] Transducer type (1A4) VEL 40 (*) Latitude (degrees north) 40.134 41 Local coordinate x (meters north) 42 (*) Longitude (degrees east) 44.724 43 Local coordinate y (meters east) 44 (*) Elevation (meters above sea-level) 1460. 45 Local coordinate z (meters down) 46 (*) Digitizing constant (counts/volt) 3276.8 47 (*) Anti-alias filter corner frequency (hertz) 50. 48 (*) Poles of anti-alias filter (roll-off=6dB/pole) 7. 49 (*) Transducer natural frequency (hertz) 1. 50 (*) Transducer damping coefficient 0.8 51 (*) Coil constant (volts/motion-unit) 1. 52 (*) Amplifier gain (dB) 60 (*) Clock correction (seconds; subtract from event time to get true time) uncertain 61 Elapsed time since last update of clock correction (seconds) uncertain 62 Recorder battery voltage (volts) 63 Desired trigger ratio STA/LTA unused 64 Actual value of STA at trigger unused 65 Actual value of LTA at trigger unused 66 Maximum value of STA/LTA during event unused Table 3-2. Listing of events recorded at 5 or more stations. EVENT G1 G2 G3 G4 G5 Jul 1990 1811602 R R R 1821226 K K k K 1841647 G G G G 1850235 G G G G G 1850700 N O N N 1850817 G H H G 1851021 K K K 1851206 K K K 1871129 E E E E E 1871224 G G G 1871936 C G G 1880740 T T T T 1890310 R R R 1891450 H I I H 1900855 D D D 1910900 G G G 1911254 G H I 1930900 N N N N N m 1930917 S S T S S s 1931442 N N N N N n 1931516 D D D D D d 1940828 F F F F 1941043 S S S 1941425 D D D D 1941516 E E E E 1950605 K K K K 1950735 Q Q Q Q 1951541 S S S 1951627 N N O 1970737 P P Q Q Q 1970937 K K K K 1971155 E E E 54O 1971159 T T A A A 1971245 R R R R 1980403 O O O 1980958 O O P P 1981146 M M L L 1981656 N N N O 1990827 H H H 2010321 H H H H 2040815 P Q P 2041224 A A A A A 2041445 M M M M M 2041527 H I I I I 2042055 O P Q O 2051003 A A A 2060741 N N N 2061111 R R A S 2070658 P P P P 2070900 G G G G 2080532 J J J J 2081256 P P P P P 2090058 H I H 2110845 C C C C C 2110920 P N N 2111303 A A B B Aug 1990 2130726 A B B A 2130820 E E E E E 2132218 M M M M 2140718 B B B C C 2140734 A A A 2140911 P P P P 2141214 R Q 15H R 2150742 N N N N 2150856 P P Q P 2151131 J I J 2201500 H H H H H g 2220908 T A A 2221157 N N O 2221246 D D D 2221555 L L L L L l 2240029 L L L 2242144 E F F 2250620 A B B 2250702 R R R R R r 2252211 K L L L L 2271313 P P P 2280209 I I I I 2280506 M N M N 2280717 M M M 2281147 F F F 2302317 F F F F 2311829 P Q Q 2312043 L M L M L 2312140 E E E 2320915 P P P P 2321127 H I I I I 2321221 N O P N 2321236 E E E 2330348 T A S 2330728 N N N 2331234 C D D 2331507 F F G 2351124 P P P 2351827 P P Q Q Q p 2352152 B B B B B 2370705 P P P P P 2371600 H H H H H 2390142 K K K K K 2390856 P P P Q P 2391048 B B B B B 2391108 L L L L L 2391229 M M M 2400335 M M N M 2400557 M M M M 2411109 N O O 2411253 G G G Sep 1990 2472255 P P P P P 2510854 O O O O O 2511938 D E D D 2531053 G G G 2540703 E E E E 2601137 S T S S T 2601347 R R R R Oct 1990 2831211 P P P P 2831217 S S S S 2880749 T S T T 2881842 O O P P O 2911121 R R R R R 2921401 E E E E E 3000549 C B B C B 3021252 N N O N 3030913 P P P P 3030932 R R Q Nov 1990 3121935 I I I J 3200659 S S S R 3201500 L L L L L 3251224 E E E E E 3261136 M M M M M 3310805 I I I I 3330518 F F F F Dec 1990 3450823 J I J J I 3460809 K K K 3461153 J I J J 3490939 B B B C 3491038 J J J J J 3491541 D D D D D 3501546 A A A A A 3510116 T T T T T 3541304 B B B B B 3572129 E E E E 3591320 T T T 3601029 J J J J 3611328 I I H 3620405 H H H Jan 1991 0011919 P O O 0070103 I I I 0070435 M M M M 0070615 T T T 0070937 N N N 0110604 K K K K 0312308 C C C C Feb 1991 0321241 R R R Mar 1991 0801040 N N N 0841345 T t T 0841353 N N N n N 0851132 T t T 0851150 K K K k K 0861351 R R R r 0862217 Q Q q Apr 1991 0930131 K K k 0940453 T T t 0950912 F G F g 1010949 T T t 1011023 E E E e 1040819 N N N n 1050813 R R r 1051053 K K k 1061256 A A A a 1071050 L L L l 1081030 O O O o 1091355 T T T a 1170332 B B b 1190913 G G g G 1191105 A a A 1191110 P p P 1191151 O o O May 1991 1211146 J J j 1211246 L L l 1211357 A A a 1212319 O O o 1220126 A A A a 1220218 K K K k 1220229 L L l 1220343 C C C c 1220431 M L L m 1220754 B B B b 1220901 C C C c 1220945 F G G g 1221158 D D D d 1221206 Q R q 1230609 E E E 1230613 L L L 1230927 28A O O 1232020 G F F G 1232341 N N N 1240454 F G F 1241330 E E E E 1241533 Q Q Q 1251146 I J I 1260755 K K K K 1261243 N O N N 1270902 B B B A 1270914 K K K K 1271324 F F F F 1280845 A B B B 1281213 K K L L 1300125 S S S 1302052 T A T T 1310558 C C C 1310633 P P P 1330829 R R R 1340937 A A A 1341238 C C C 1350839 B B B 1351242 O O O O 1351429 I I J I 1361148 G G G G 1501038 E E E E 1510919 M M M 1511228 H H H Jun 1991 1541022 R R S S 1541031 O O P O 1541046 F F F F 1541144 E E E 1550055 K K K K 1550114 F F F F 1550642 C C C C 1550708 L L L L 1571348 P P P P 1590112 E E E E 1592107 L L M M 1621053 O O O O 1631518 N O O O 1640433 G G G G 1640603 R R R 1641137 L L L L 1660059 R R R R 1660250 J J I J 1660258 Q Q Q 1670453 T T T 1681239 C D C 1681349 H H H H 1700640 Q R R R 1721154 L L L 1721202 S S S S 1721443 A A A A 1730543 E E E E 1760754 H H H 1781409 D D D D Jul 1991 1841301 E E F E 1850627 D D D D 1851449 O O O O 1870748 R R R 1950913 O O O 1961300 S S S 2021851 I I I Nov 1991 3052110 C C C 3121119 P P P 3160812 G G G 3162036 I J I 3321721 J K K Dec 1991 3420103 C C C 3471910 M M M 3501949 R R R Feb 1992 0340623 M M M 0411512 I I I 0501109 T T T 0562202 J J J Mar 1992 0621241 A A A 0871921 P P P Apr 1992 0950217 H G H 0961014 O O O 0971048 K L K 0992221 D D D 0992252 R Q Q 1061504 O O O 1150712 G G H 1171316 P P P 1190844 J J J May 1992 1260622 D D D 1261953 G F F 1281916 F F F 1331659 C C C 1360812 Q P P 1411225 L L L Capital letter indicates both stations A & B. Lower case letter indicates station A only. In 1971154O.G5 the event signal arrived during a sensor calibration. Table 3-3. Listing of all included records (events, calibrations, and noise tests). EVENT G1 G2 G3 G4 G5 G7 GA GB GC GD 1780731 G 1780732 C 1781338 S 1781356 A a 1790322 D d 1791622 N 1792335 A 1800007 K 1800147 S 1801230 S 1810343 N 1810815 T 1810816 P 1810906 L 07G 1811034 G 1811035 C 1811214 C 1811602 R R R 1811636 B 1821138 P 1821139 L 1821219 B 1821219 R 1821226 K K k K 1821238 P 1821239 K 1821301 F 1821302 B 1821721 E 1822118 F G 1830616 B 1830616 R 1830808 C 1830808 S 1830847 N 1830957 K 1831221 F 1831225 I 1840721 R 1840722 N 1841207 E 1841208 A 1841647 G G G G 1850133 C C 1850235 G G G G G 1850700 N O N N 1850817 G H H G 1851021 K K K 1851108 J 1851109 F 1851206 K K K 1860508 A 1860508 Q 1860833 S 1860918 B 1860918 R 1861011 E 1861057 I L 1870512 Q 1870725 R 1870726 N 1871129 E E E E E 1871224 G G G 1871234 c 1871234 s 1871936 C G G 1872240 A 1880147 E 1880740 T T T T 1881350 N 1890310 R R R 1891450 H I I H 1900743 L L 1900855 D D D 1901518 J K 1910900 G G G 1911254 G H I 1920437 O 1920712 s 1920713 o 1920805 A 1920805 Q 1920854 A 1920854 Q 1920904 H 1920905 D 1922359 T 1930900 N N N N N m 1930917 S S T S S s 1930923 D 1931442 N N N N N n 1931516 D D D D D d 1931638 O 1932058 T 1932155 B 1940343 H 1940522 I 1940523 E 1940828 F F F F 1940836 C 1941043 S S S 1941251 Q 1941425 D D D D 1941433 G 1941516 E E E E 1950605 K K K K 1950735 Q Q Q Q 1951021 S 1951541 S S S 1951627 N N O 1970538 R 1970539 N 1970545 J 1970546 E 1970549 A 1970549 Q 1970552 S 1970553 O 1970627 N 1970628 J 1970633 C 1970633 S 1970649 F 1970650 B 1970737 P P Q Q Q 1970835 E E 1970937 K K K K 1971047 c 1971154 O 1971155 E E E 1971155 K 1971159 T T A A A 1971245 R R R R 1971342 G G 1971956 J 1980403 O O O 1980958 O O P P 1981134 K N 1981146 M M L L 1981149 B 1981204 Q 1981656 N N N O 1982125 R 1990003 M 1990811 H H 1990827 H H H 1991007 C 1991132 K 1991306 K 2000237 K K 2000540 S 2000541 O 2000549 N 2000550 J 2000843 q 2000844 m 2010321 H H H H 2011731 I I 2022233 P P 2022305 H H 2030242 L 2030947 J 2031131 F 2040815 P Q P 2041113 K 2041114 G 2041224 A A A A A 2041445 M M M M M 2041527 H I I I I 2042055 O P Q O 2051003 A A A 2051040 H 2051041 D 2060638 O 2060741 N N N 2060916 t 2060917 p 2061015 H 2061016 D 2061108 09B Q 2061111 R R A S 2061451 P O 2070558 K 2070559 G 2070658 P P P P 2070900 G G G G 2070917 F E 2071030 H 2080532 J J J J 2080656 B C 2081149 r 2081150 n 2081256 P P P P P 2081325 Q Q 2082307 I I 2090058 H I H 2091131 N 2091132 I 2091922 F 2100329 M 2100634 G 2100635 C 2102138 E E 2110845 C C C C C 2110920 P N N 2111303 A A B B 2120625 R R 2121143 T T 2130555 M 2130556 I 2130726 A B B A 2130820 E E E E E 2131835 G 2132218 M M M M 2132304 B 2140317 G F 2140718 B B B C C 2140734 A A A 2140911 P P P P 2140920 G 2141214 R Q 15H R 2141653 J 2141713 O P 2142118 E F 2142125 F 2150742 N N N N 2150856 P P Q P 2150921 D 2151126 L 2151131 J I J 2151133 I 2152129 N 2170753 H 2170754 D 2170811 F 2170812 B 2170819 B 2170819 Q 2170936 d 2170936 t 2180205 Q Q 2180716 F F 2180846 H H 2181126 G 2190033 J J 2191020 A A 2201000 F 2201001 B 2201500 H H H H H g 2211305 C C 2220237 B B 2220814 J 2220908 T A A 2221044 F 2221157 N N O 2221246 D D D 2221555 L L L L L l 2221556 S 2222118 S 2240029 L L L 2242144 E F F 2250547 B 2250547 R 2250620 A B B 2250702 R R R R R r 2251056 K K 2252211 K L L L L 2260055 L O 2260949 C 2260949 S 2261055 G 2261523 S 2262035 S 2271036 H 2271313 P P P 2272319 P 2280058 K 2280209 I I I I 2280506 M N M N 2280717 M M M 2280751 O O 2280752 E 2280938 P P 2281047 T 2281147 F F F 2301902 E 2302317 F F F F 2310730 D 2310730 T 2310858 P 2310859 L 2310950 k 2310951 g 2311829 P Q Q 2312043 L M L M L 2312140 E E E 2312315 E E 2320014 E F 2320915 P P P P 2321127 H I I I I 2321221 N O P N 2321236 E E E 2330117 B B 2330348 T A S 2330728 N N N 2331234 C D D 2331507 F F G 2332135 T 2340051 E 2340705 C C 2340718 F F 2340753 H H 2340909 P 2350851 C 2350851 S 2350917 O 2350918 K 2350922 D 2350922 T 2350925 A 2350929 H H 2350929 O O 2350935 C 2350935 S 2350952 f 2350953 b 2351124 P P P 2351827 P P Q Q Q p 2352141 S 2352152 B B B B B 2360156 G 2370705 P P P P P 2371349 T 2371600 H H H H H 2381234 G 2390142 K K K K K 2390737 B 2390737 Q 2390856 P P P Q P 2391048 B B B B B 2391108 L L L L L 2391229 M M M 2392130 T T 2400335 M M N M 2400557 M M M M 2401235 Q 2410717 K K 2411109 N O O 2411253 G G G 2412053 M 2421110 N 2421111 J 2421116 A 2421116 P 2421159 I 2421200 E 2421206 Q 2421207 M 2440743 Q Q Q 2460245 I 2460814 I 2461013 F 2461159 Q Q Q 2462203 L 2470031 J 2470731 H H H 2470900 T 2470901 P 2471225 B 2471225 Q 2472255 P P P P P 2481201 B 2481201 R 2481302 L 2491050 S S 2491126 I 2491155 M 2491212 B S 2491225 E E 2500019 L L 2500903 D 2510854 O O O O O 2511938 D E D D 2520224 B 2530705 G G 2531053 G G G 2540703 E E E E 2540849 Q 2540850 M 2560641 S S 2561113 J 2561113 K 2561113 Q 2561114 F 2561114 G 2561114 M 2561119 C 2561119 S 2572046 C 2600518 A 2600518 G 2600518 Q 2600519 B 2600533 T 2600534 O 2600536 C 2600536 R 2600537 A 2600537 Q 2600806 L L 2601137 S T S S T 2601208 M M 2601347 R R R R 2610818 Q Q Q Q Q 2610825 Q Q Q P P 2610832 Q Q P P P 2621235 H 2641000 G 2641101 A A 2641708 H 2650246 L L 2651531 E 2651531 T 2651910 I 2651911 E 2761059 T 2761100 P 2780757 B B 2810456 M L 2810924 M 2810925 I 2821046 C 2831051 R 2831211 P P P P 2831217 S S S S 2831909 J J 2851232 K K 2861637 N 2861638 J 2871808 A 2871808 P 2871917 N 2871918 I 2880749 T S T T 2881842 O O P P O 2911121 R R R R R 2921052 I 2921401 E E E E E 2980458 M N 2991049 M 3000549 C B B C B 3021252 N N O N 3030913 P P P P 3030932 R R Q 3041220 B 3091218 T T 3100712 T 3121935 I I I J 3161234 G G 3180629 M 3180630 I 3200659 S S S R 3200709 Q Q 3201500 L L L L L 3210756 S 3210757 O 3240804 K 3240805 G 3242020 S 3242021 O 3251224 E E E E E 3261136 M M M M M 3301221 O 3310805 I I I I 3330518 F F F F 3331036 B B 3341206 S S 3370827 L L 3421143 J 3440947 L 3450823 J I J J I 3450948 M 3460809 K K K 3461153 J I J J 3490939 B B B C 3491038 J J J J J 3491541 D D D D D 3501546 A A A A A 3502105 O 3510116 T T T T T 3511742 R 3520626 T 3520627 P 3520636 O 3520637 K 3541304 B B B B B 3541940 Q 3551143 B 3572129 E E E E 3590826 A 3591107 M 3591320 T T T 3600628 I 3600629 E 3601029 J J J J 3611328 I I H 3620405 H H H 3620945 K 3621212 S 3631154 C C 3632200 B B 0010817 K 0011919 P O O 0040823 S 0040824 O 0070103 I I I 0070435 M M M M 0070615 T T T 0070817 A 0070937 N N N 0081055 Q Q 0090811 T 0090812 P 0090817 Q 0090818 M 0090825 I 0090826 E 0101528 S 0110604 K K K K 0112102 S S 0131532 H 0131533 D 0140850 T 0211126 F 0261701 B 0280632 K 0280633 G 0291120 E 0291139 R 0291744 A 0292000 F 0300435 J 0311207 H H 0312308 C C C C 0320535 P Q 0321024 O O 0321241 R R R 0360438 J 0370210 A 0370707 M 0370708 I 0370714 H 0370715 D 0421318 I 0511321 N 0520814 Q 0520815 M 0550631 M 0550743 T 0570730 F 0591144 K 0591230 N 0611027 I 0731053 H 0731110 Q Q N 0800747 L 0800748 H 0800934 P P 0801040 N N N 0811404 N N 0821025 E 0841345 T T T 0841353 N N N N N 0851132 T T T 0851150 K K K K K 0851424 M M 0860910 M 0860911 I 0861351 R R R R 0862217 Q Q Q 0871139 R 0881328 A B 0881423 O O 0900730 G 0910906 B 0910913 Q 0910914 M 0910916 J 0910917 F 0910923 H 0910924 C 0930131 K K k 0940453 T T t 0940902 M m 0941339 M 0950912 F G F g 0950922 N 1010949 T T t 1011023 E E E e 1020312 B 1040819 N N N n 1050813 R R r 1051053 K K k 1061256 A A A a 1071050 L L L l 1081030 O O O o 1091355 T T T a 1122309 B 1130933 D 1160851 K 1160852 F 1160857 I 1160858 E 1160902 J 1160903 F 1160914 K 1160915 G 1170332 B B b 1181402 A 1190857 K 1190913 G G g G 1191053 F f 1191105 A a A 1191110 P p P 1191151 O o O 1191200 J 1191443 N 1191823 Q 1191831 F 1210905 A 1210905 P 1210914 J 1210915 F 1210918 I 1210919 E 1211146 J J j 1211246 L L l 1211357 A A a 1211447 J 1211448 F 1212319 O O o 1220126 A A A a 1220208 F 1220218 K K K k 1220229 L L l 1220343 C C C c 1220431 M L L m 1220754 B B B b 1220901 C C C c 1220945 F G G g 1220948 F 1221042 Q q 1221124 O 1221125 K 1221131 I 1221132 E 1221134 M 1221137 J 1221138 F 1221158 D D D d 1221206 Q R q 1221242 K 1221243 F 1230609 E E E 1230613 L L L 1230927 O O 1230928 A 1231140 H 1232020 G F F G 1232341 N N N 1240454 F G F 1241330 E E E E 1241509 P 1241510 L 1241520 O 1241521 K 1241533 Q Q Q 1250515 I I 1250708 L 1250709 C 1250750 I 1250751 E 1250908 Q R 1251146 I J I 1252007 R R 1260755 K K K K 1260806 N 1260807 J 1261241 G 1261243 N O N N 1270857 A A 1270902 B B B A 1270914 K K K K 1271017 J 1271324 F F F F 1280845 A B B B 1281057 M 1281110 G G 1281213 K K L L 1300125 S S S 1302031 H H 1302052 T A T T 1302055 C 1310457 O O 1310458 G 1310558 C C C 1310633 P P P 1330829 R R R 1340937 A A A 1340939 G 1341155 F G 1341238 C C C 1350839 B B B 1350852 J 1350853 F 1350859 B 1350907 H 1350908 D 1351242 O O O O 1351429 I I J I 1361148 G G G G 1380322 P 1400802 E 1411738 J J 1412019 G G 1412345 E 1420151 N N 1420822 F 1440800 B 1440843 I 1441104 O 1461429 M 1470341 D 1470649 D 1500725 M 1500726 I 1500734 D 1500734 T 1500744 N 1500745 J 1500750 D 1500750 T 1500758 O 1500759 K 1501038 E E E E 1510919 M M M 1511228 H H H 1541022 R R S S 1541031 O O P O 1541046 F F F F 1541144 E E E 1550055 K K K K 1550114 F F F F 1550642 C C C C 1550708 L L L L 1550851 S 1550852 O 1550855 N 1550856 J 1550857 J 1550858 F 1561113 A 1570855 M M 1571348 P P P P 1590112 E E E E 1590113 O 1592107 L L M M 1592110 F 1621053 O O O O 1621322 K 1630635 M 1630636 I 1630816 I I 1631518 N O O O 1640433 G G G G 1640603 R R R 1641137 L L L L 1650837 H H 1660059 R R R R 1660250 J J I J 1660258 Q Q Q 1660626 I I 1660720 K 1661200 K 1661556 J J 1670453 T T T 1671107 I 1671356 O 1680305 F 1681038 M 1681039 I 1681043 I 1681044 E 1681048 J 1681049 F 1681053 I 1681054 E 1681239 C D C 1681349 H H H H 1700640 Q R R R 1701242 L 1701308 K 1710750 N N 1711219 Q Q 1711336 N N 1721154 L L L 1721202 S S S S 1721443 A A A A 1730543 E E E E 1750728 I 1750729 E 1760754 H H H 1761250 A 1781409 D D D D 1790710 K 1790711 G 1812010 B B 1820716 M 1820717 I 1831052 A 1841301 E E F E 1850627 D D D D 1850851 L 1851449 O O O O 1870748 R R R 1890623 L 1890624 H 1890629 J 1890630 F 1891036 J 1891037 F 1940553 Q R 1941406 O 1941407 K 1950913 O O O 1951547 F F 1961021 I 1961022 E 1961300 S S S 1962046 B B 1970404 M 1970453 T T 1991102 L 1991102 T 1991103 H 1991103 P 1991311 C 2021851 I I I 2041954 K K 2050324 F F 2051156 S S 2060452 S S 2061130 O O 2150927 C C 2180920 Q 2181553 S 2220858 M N 2221046 F 2221048 P Q 2221054 P 2221109 A A 2221123 K K 2261255 K 2270330 K 2320851 H 2331202 K 2371023 S 2371024 O 2371032 M 2371033 I 2371039 M 2371040 I 2371045 M 2371046 H 2381228 R R 2401047 M N 2401148 R 2411238 H 2420838 N 2430933 O 2442049 H 2451040 M M 2470914 F 2481213 F F 2481923 R R 2502346 N 2502347 J 2511019 N 2532203 H I 2671737 A 2680311 K 2680312 G 2710527 B 2710602 H 2730540 H 2740812 K 2761424 T T 2761504 Q Q 2790140 K 2790147 D D 2790150 E 2790326 L 2790415 C 2800746 L 2800747 H 2800750 I 2800751 E 2800915 L 2810342 H 2821019 D 2821019 T 2830245 D 2830929 M 2830930 H 2840959 J 2841000 F 2900841 L 2900842 H 2900900 K 2900901 F 2900919 I 2900920 D 2961003 I 2961004 D 2981151 Q 2981152 M 3021201 B 3021201 R 3021238 T 3021239 P 3051350 F F 3051431 E 3052110 C C C 3060945 Q 3081040 T A 3091231 C D 3121004 S S 3121119 P P P 3130453 L L 3141020 D D 3160812 G G G 3162036 I J I 3171119 H 3171124 E 3220624 C 3231004 K K 3251250 M 3290720 N 3290721 J 3301213 A 3301255 B B 3311142 G 3321721 J K K 3331219 S 3331241 Q 3331242 N 3331323 N N 3340401 I 3340848 P P 3341309 C 3350918 L 3361220 I I 3370753 Q 3370754 L 3371054 Q 3381301 K K 3391111 D 3400740 L 3411210 I 3411427 H 3420103 C C C 3420757 L 3450707 O 3450708 K 3451444 B 3451506 G 3470556 T 3471910 M M M 3472006 M 3472009 Q 3501543 G I 3501949 R R R 3501959 J K 3511149 T 3530145 C 3540615 S S 3540847 B 3560854 N 3571321 L 3601147 G 3610917 C 3630052 L 0022221 P P 0022222 F G 0022235 Q 0030028 Q 0030040 L 0030446 L 0060152 B 0070140 G 0070544 C 0070614 H 0331138 I 0331139 E 0331147 T 0331148 P 0331335 T 0331336 P 0340027 B B 0340623 M M M 0340627 K K 0350831 S S 0350837 B B 0350928 L L 0351100 A A 0351210 I I 0360921 H 0361322 S T 0410401 K K 0411512 I I I 0452032 E 0461253 O O 0461331 I I 0461338 K J 0461518 M M 0480551 L 0490140 B 0500807 N 0500808 I 0501109 T T T 0501446 E 0510103 D 0510816 F 0511143 P 0511240 T 0511333 M 0511720 I J 0520037 H 0520145 D D 0541104 Q 0541204 R 0542350 D 0560751 K 0560755 K 0561444 H 0562202 J J J 0570128 M 0570351 M 0570934 E E 0571107 R 0590903 Q 0610914 P Q 0620606 Q 0621241 A A A 0630137 F 0650330 P P 0670937 D D 0672128 O 0731719 O 0841029 J 0841030 F 0841034 B 0841034 R 0841040 I 0841041 E 0851051 C 0851152 R 0860233 J K 0861039 B 0871921 P P P 0880546 Q Q 0911020 Q Q 0920826 A 0950217 H G H 0950505 L 0951228 M M 0961014 O O O 0971048 K L K 0992119 R 0992221 D D D 0992238 G H 0992252 R Q Q 0992307 K 0992332 C 1010801 M 1010802 I 1010802 M 1010803 I 1051350 K 1060920 R 1061227 B B 1061504 O O O 1081146 A A 1121124 P 1130305 B 1131226 K 1150712 G G H 1171316 P P P 1190844 J J J 1201057 M M 1201501 L 1211148 H 1212351 I 1221212 L 1260551 Q 1260552 M 1260604 R 1260605 N 1260622 D D D 1261110 O 1261953 G F F 1271241 J 1281039 T S 1281916 F F F 1310409 K K 1330718 J 1331659 C C C 1340629 R 1340630 N 1341447 F F 1350323 D D 1360812 Q P P 1381001 I I 1381027 M N 1401228 L L 1411220 T T 1411225 L L L 1421123 N 1471858 E D 1480803 F 1490801 K K 1531113 F 1791349 R 1791350 N 1791450 P 1791451 L 1950617 I 1950713 Q 2200627 T 2201426 Q 2201427 M 2211425 D D 2230736 K 2230737 F 2231347 B Capital letter indicates both stations A & B. Lower case letter indicates station A only. Table 3-4. Estimated or Reported 1991 Master-Clock Resynchs. Time Range Estimated Change day hr mn day hr mn (ms) 084 05 35 084 07 08 -8 086 08 54 086 09 10 -7 091 03 48 091 06 58 -4 095 08 34 095 09 40 -2 098 12 34 098 15 44 -6 108 06 54 108 10 04 -13 116 09 13 116 21 14 -8 125 23 47 126 08 05 -5 149 22 05 150 07 57 -39 153 20 21 154 08 22 -6 160 21 29 161 09 30 -12 169 23 07 170 11 08 -5 175 04 33 175 07 28 -6 176 07 41 176 19 42 -5 Time Before After Change day hr mn (ms) (ms) (ms) 283 19 12 3.3 0.1 -3.2 284 19 48 4.4 -0.1 -4.5 290 06 58 11.0 -0.1 -11.1 294 06 45 8.0 -0.1 -8.1 298 07 20 5.0 0.1 -4.9 301 07 07 5.6 -0.4 -6.0 303 06 50 4.2 -0.2 -4.4 309 07 11 7.3 -0.1 -7.4 310 07 00 2.3 -0.4 -2.7 311 10 00 2.0 -0.4 -2.4 316 07 11 6.0 0.4 -5.6 Table 3-5a. NEIC Parameters of Identified Events Sorted by Date. Date D.o.Y. Hr Mn Sec Latitude Longitude Depth Mag Azi Epicentral Distance Travel Phase Region deg. deg. km deg. km deg. m:ss 28 - JUN - 90 (179) 03: 20: 35.0 37 .085 N 49 .642 E 10 G 4.8 307 545 4.90 1:36 P CASPIAN SEA 28 - JUN - 90 (179) 03: 42: 01.9 * 37 .079 N 50 .147 E 10 G 4.7 304 581 5.22 1:39 P CASPIAN SEA 01 - JUL - 90 (182) 12: 24: 57.2 37 .181 N 49 .885 E 10 G 4.8 305 555 4.99 1:35 P CASPIAN SEA 01 - JUL - 90 (182) 17: 19: 44.1 37 .280 N 48 .818 E 10 G 4.6 310 476 4.28 1:30 P CASPIAN SEA 01 - JUL - 90 (182) 21: 16: 48.3 37 .285 N 48 .820 E 10 G 4.7 310 476 4.28 1:29 P CASPIAN SEA 04 - JUL - 90 (185) 02: 24: 41.9 25 .372 N 124 .473 E 133 5.6 256 7392 66.47 10:38 P NORTHEAST OF TAIWAN 06 - JUL - 90 (187) 05: 02: 27.9 45 .371 N 150 .170 E 42 D 5.7 226 7961 71.59 11:22 P KURIL ISLANDS 06 - JUL - 90 (187) 19: 34: 52.4 36 .861 N 49 .303 E 35 D 5.3 311 540 4.85 1:16 Pn WESTERN IRAN 09 - JUL - 90 (190) 15: 11: 20.3 5 .395 N 31 .654 E 13 G 6.4 22 4078 36.67 7:09 P SUDAN 11 - JUL - 90 (192) 04: 36: 08.6 * 37 .015 N 49 .530 E 33 N 4.5 308 543 4.88 1:35 P CASPIAN SEA 13 - JUL - 90 (194) 14: 20: 43.4 36 .415 N 70 .789 E 217 D 5.6 272 2304 20.72 4:28 P HINDU KUSH REGION 14 - JUL - 90 (195) 05: 54: 25.4 0 .003 N 17 .376 W 11 G 6.4 71 7676 69.03 11:07 P NORTH OF ASCENCION ISLAND 14 - JUL - 90 (195) 07: 24: 39.6 0 .074 S 17 .523 W 12 G 5.8 71 7694 69.19 11:10 P NORTH OF ASCENCION ISLAND 16 - JUL - 90 (197) 07: 26: 34.6 15 .679 N 121 .172 E 25 D 7.9 266 7752 69.71 11:12 P "LUZON, PHILIPPINE ISLANDS" 16 - JUL - 90 (197) 13: 31: 13.2 16 .285 N 120 .457 E 13 D 5.7 266 7650 68.79 11:04 P "LUZON, PHILIPPINE ISLANDS" 16 - JUL - 90 (197) 19: 45: 25.1 16 .365 N 120 .546 E 33 N 5.4 266 7652 68.81 11:04 P "LUZON, PHILIPPINE ISLANDS" 17 - JUL - 90 (198) 04: 02: 09.2 37 .137 N 49 .979 E 33 N 4.6 304 565 5.08 1:35 P CASPIAN SEA 17 - JUL - 90 (198) 21: 14: 43.8 16 .495 N 120 .981 E 23 G 6.7 266 7680 69.07 11:09 P "LUZON, PHILIPPINE ISLANDS" 18 - JUL - 90 (199) 08: 00: 12.8 16 .511 N 121 .007 E 14 G 5.8 266 7681 69.08 11:10 P "LUZON, PHILIPPINE ISLANDS" 18 - JUL - 90 (199) 11: 29: 24.9 36 .990 N 29 .595 E 17 D 5.2 80 1359 12.22 3:07 P TURKEY 20 - JUL - 90 (201) 17: 30: 36.2 ? 42 .10 N 46 .77 E 33 N 4.2 217 278 2.50 0:50 P EASTERN CAUCASUS 22 - JUL - 90 (203) 09: 26: 14.6 23 .622 S 179 .893 W 531 G 5.9 260 15477 139.18 21:14 SKP SOUTH OF FIJI ISLANDS 22 - JUL - 90 (203) 11: 20: 09.6 16 .532 N 121 .045 E 33 N 5.3 266 7683 69.09 11:07 P "LUZON, PHILIPPINE ISLANDS" 23 - JUL - 90 (204) 20: 54: 56.6 42 .719 N 45 .947 E 33 N 4.8 199 305 2.74 0:47 Pn EASTERN CAUCASUS 26 - JUL - 90 (207) 06: 53: 56.3 27 .247 N 65 .508 E 19 G 5.8 300 2388 21.47 4:51 P PAKISTAN <2 events> 27 - JUL - 90 (208) 05: 31: 00.1 37 .318 N 49 .585 E 10 G 4.8 305 525 4.72 1:29 P CASPIAN SEA 27 - JUL - 90 (208) 12: 37: 59.5 15 .355 S 167 .464 E 126 G 7.5 261 13866 124.70 18:48 PKP VANUATU ISLANDS 02 - AUG - 90 (214) 17: 12: 48.5 * 38 .540 N 48 .186 E 33 N 4.2 300 346 3.12 0:56 P N.W. IRAN-USSR BORDER REGION 02 - AUG - 90 (214) 21: 17: 18.7 * 38 .398 N 48 .228 E 33 N 4.1 301 358 3.22 0:55 P N.W. IRAN-USSR BORDER REGION 03 - AUG - 90 (215) 09: 15: 06.1 47 .963 N 84 .961 E 33 G 6.1 241 3291 29.59 6:05 P KAZAKH-XINJIANG BORDER REGION 10 - AUG - 90 (222) 15: 44: 31.3 0 .333 N 126 .175 E 53 6.4 275 9258 83.25 12:25 P MOLUCCA PASSAGE 10 - AUG - 90 (222) 21: 11: 49.0 6 .572 N 60 .240 E 10 G 5.5 333 4040 36.33 7:07 P CARLSBERG RIDGE 12 - AUG - 90 (224) 21: 25: 21.9 19 .435 S 169 .132 E 140 G 6.3 263 14283 128.44 18:52 PKP VANUATU ISLANDS <2 events> 13 - AUG - 90 (225) 06: 18: 25.1 36 .663 N 49 .884 E 35 * 4.6 309 592 5.33 1:37 P WESTERN IRAN 14 - AUG - 90 (226) 00: 50: 39.2 27 .024 N 65 .969 E 21 D 5.2 300 2438 21.93 4:56 P PAKISTAN 14 - AUG - 90 (226) 15: 13: 28.6 35 .432 N 35 .648 W 10 G 6.0 114 6833 61.45 10:27 P NORTH ATLANTIC RIDGE 15 - AUG - 90 (227) 23: 08: 56.0 43 .757 N 143 .297 E 162 D 5.4 230 7637 68.68 10:51 P "HOKKAIDO, JAPAN REGION" 16 - AUG - 90 (228) 04: 59: 57.6 41 .564 N 88 .770 E 0 G 6.2 253 3668 32.98 6:39 P "SOUTHERN XINJIANG, CHINA" 20 - AUG - 90 (232) 12: 20: 11.0 * 36 .956 N 49 .720 E 33 N 4.8 308 560 5.03 1:30 P WESTERN IRAN 21 - AUG - 90 (233) 03: 47: 26.2 37 .309 N 49 .685 E 10 G 4.8 305 533 4.79 1:30 P CASPIAN SEA 22 - AUG - 90 (234) 07: 51: 49.5 * 37 .056 N 49 .327 E 10 G 4.3 309 526 4.73 1:33 P CASPIAN SEA 25 - AUG - 90 (237) 15: 47: 53.8 0 .525 N 126 .084 E 11 G 6.5 275 9236 83.06 12:29 P MOLUCCA PASSAGE 29 - AUG - 90 (241) 20: 44: 23.0 11 .791 N 95 .034 E 25 D 5.2 288 5830 52.43 9:15 P ANDAMAN ISLANDS REGION 03 - SEP - 90 (246) 02: 40: 59.1 36 .409 N 70 .671 E 202 D 4.9 272 2294 20.63 4:27 P HINDU KUSH REGION 07 - SEP - 90 (250) 00: 12: 26.2 5 .443 N 31 .686 E 10 G 5.2 22 4072 36.62 7:09 P SUDAN 08 - SEP - 90 (251) 19: 33: 18.8 27 .500 N 66 .092 E 28 * 5.5 299 2412 21.69 4:52 P PAKISTAN 09 - SEP - 90 (252) 02: 14: 51.0 56 .654 N 34 .395 W 10 G 5.4 137 5765 51.84 9:14 P NORTH ATLANTIC OCEAN 14 - SEP - 90 (257) 20: 40: 18.3 13 .382 N 51 .456 E 10 G 5.4 346 3046 27.39 5:50 P EASTERN GULF OF ADEN 17 - SEP - 90 (260) 11: 57: 24.1 5 .917 S 103 .796 E 59 D 5.7 296 7902 71.06 11:14 P SOUTHERN SUMATERA 22 - SEP - 90 (265) 02: 46: 01.2 * 42 .538 N 46 .449 E 33 N 4.3 208 304 2.73 0:34 P EASTERN CAUCASUS 24 - SEP - 90 (267) 06: 35: 13.9 * 38 .253 N 47 .951 E 10 G 4.6 306 348 3.13 P NORTHWESTERN IRAN 25 - OCT - 90 (298) 04: 52: 06.0 * 76 .243 N 8 .409 E 10 G 4.6 167 4382 39.41 ?7:47 P SVALBARD REGION 25 - OCT - 90 (298) 04: 53: 59.9 35 .121 N 70 .486 E 114 G 6.0 276 2327 20.93 4:38 P HINDU KUSH REGION 12 - NOV - 90 (316) 12: 28: 51.5 42 .959 N 78 .071 E 19 G 6.3 252 2774 24.95 5:28 P ALMA-ATA REGION 16 - DEC - 90 (350) 15: 45: 40.7 41 .361 N 43 .715 E 33 N 5.2 148 161 1.45 0:21 P TURKEY-USSR BORDER REGION 23 - DEC - 90 (357) 21: 28: 50.7 * 42 .115 N 44 .356 E 33 N 4.1 172 222 2.00 0:23 P WESTERN CAUCASUS 27 - DEC - 90 (361) 13: 26: 57.1 36 .539 N 48 .907 E 10 G 4.7 316 541 4.87 1:26 P NORTHWESTERN IRAN 28 - DEC - 90 (362) 04: 03: 53.6 37 .106 N 49 .227 E 10 G 5.0 309 516 4.64 1:29 P CASPIAN SEA Date D.o.Y. Hr Mn Sec Latitude Longitude Depth Mag Azi Epicentral Distance Travel Phase Region deg. deg. km deg. km deg. m:ss 01 - JAN - 91 (001) 19: 18: 56.4 39 .822 N 48 .439 E 61 D 4.9 275 318 2.86 0:48 P N.W. IRAN-USSR BORDER REGION 31 - JAN - 91 (031) 23: 03: 33.6 35 .993 N 70 .423 E 142 G 6.7 273 2288 20.57 4:31 P HINDU KUSH REGION 26 - FEB - 91 (057) 07: 25: 47.2 40 .186 N 13 .822 E 401 5.5 100 2613 23.49 4:30 P TYRRHENIAN SEA 27 - MAR - 91 (086) 22: 17: 55.0 40 .443 N 45 .443 E 33 N 4.3 240 70 0.63 -0:08 P EASTERN CAUCASUS 14 - APR - 91 (104) 08: 08: 55.7 27 .155 N 127 .419 E 83 G 6.2 253 7519 67.62 10:45 P RYUKYU ISLANDS 15 - APR - 91 (105) 10: 48: 59.3 36 .340 N 71 .358 E 124 D 5.3 272 2355 21.18 4:30 P AFGHANISTAN-USSR BORDER REGION 27 - APR - 91 (117) 03: 31: 58.5 * 40 .093 N 43 .719 E 10 G 4.2 87 86 0.77 0:07 P TURKEY-USSR BORDER REGION 29 - APR - 91 (119) 09: 12: 48.1 42 .453 N 43 .673 E 17 G 7.2 162 272 2.45 0:29 P WESTERN CAUCASUS 29 - APR - 91 (119) 10: 52: 42.2 42 .712 N 44 .102 E 10 G 4.6 170 291 2.62 0:32 P WESTERN CAUCASUS 29 - APR - 91 (119) 11: 04: 28.9 * 42 .510 N 43 .816 E 10 G 4.3 164 275 2.47 0:35 P WESTERN CAUCASUS 29 - APR - 91 (119) 11: 10: 11.9 42 .584 N 43 .904 E 10 G 4.7 166 281 2.53 0:35 P WESTERN CAUCASUS 29 - APR - 91 (119) 11: 51: 10.3 42 .572 N 43 .816 E 10 G 4.9 165 281 2.53 0:34 P WESTERN CAUCASUS 29 - APR - 91 (119) 11: 59: 54.8 42 .625 N 43 .962 E 10 G 4.5 167 284 2.56 0:34 P WESTERN CAUCASUS 29 - APR - 91 (119) 14: 43: 06.3 42 .515 N 43 .937 E 10 G 5.4 166 273 2.45 0:35 P WESTERN CAUCASUS 29 - APR - 91 (119) 18: 23: 15.2 42 .583 N 43 .764 E 10 G 5.5 164 284 2.55 0:35 P WESTERN CAUCASUS 29 - APR - 91 (119) 18: 30: 41.5 42 .503 N 43 .899 E 14 G 6.0 166 272 2.45 0:36 P WESTERN CAUCASUS 01 - MAY - 91 (121) 23: 19: 11.8 * 42 .719 N 44 .053 E 10 G 4.1 169 293 2.63 0:29 P WESTERN CAUCASUS 02 - MAY - 91 (122) 01: 25: 30.1 42 .541 N 43 .960 E 10 G 5.1 167 275 2.47 0:32 P WESTERN CAUCASUS 02 - MAY - 91 (122) 02: 07: 31.6 ? 41 .34 N 45 .17 E 10 G 4.3 196 139 1.25 0:45 P EASTERN CAUCASUS 02 - MAY - 91 (122) 02: 18: 00.1 * 42 .211 N 43 .906 E 10 G 4.1 164 241 2.17 0:32 P WESTERN CAUCASUS 02 - MAY - 91 (122) 03: 42: 26.1 * 42 .608 N 43 .477 E 10 G 4.0 160 294 2.64 0:42 P WESTERN CAUCASUS 02 - MAY - 91 (122) 04: 30: 53.9 * 42 .481 N 43 .201 E 10 G 3.9 155 290 2.61 0:41 P WESTERN CAUCASUS 02 - MAY - 91 (122) 09: 00: 35.2 * 42 .704 N 43 .692 E 10 G 4.1 164 298 2.68 0:33 P WESTERN CAUCASUS 02 - MAY - 91 (122) 09: 44: 41.4 42 .507 N 43 .507 E 10 G 4.5 159 283 2.54 0:36 P WESTERN CAUCASUS 03 - MAY - 91 (123) 06: 08: 37.1 42 .482 N 43 .363 E 10 G 4.6 157 285 2.56 0:37 P WESTERN CAUCASUS 03 - MAY - 91 (123) 06: 12: 54.2 ? 41 .93 N 43 .80 E 33 N 4.2 159 214 1.93 0:41 P TURKEY-USSR BORDER REGION 03 - MAY - 91 (123) 20: 19: 38.8 42 .683 N 43 .247 E 10 G 5.3 157 309 2.78 0:38 P WESTERN CAUCASUS 03 - MAY - 91 (123) 23: 41: 01.8 42 .647 N 43 .263 E 11 D 5.2 157 305 2.74 0:39 P WESTERN CAUCASUS 04 - MAY - 91 (124) 04: 53: 35.6 ? 42 .15 N 43 .51 E 10 G 4.2 156 246 2.21 0:41 P WESTERN CAUCASUS 07 - MAY - 91 (127) 09: 01: 23.6 * 42 .606 N 43 .125 E 10 G 4.2 155 306 2.75 0:38 P WESTERN CAUCASUS 10 - MAY - 91 (130) 01: 25: 15.6 42 .496 N 43 .153 E 10 G 4.6 154 294 2.64 0:40 P WESTERN CAUCASUS 10 - MAY - 91 (130) 20: 30: 45.3 42 .627 N 43 .449 E 28 D 4.4 159 297 2.67 0:35 P WESTERN CAUCASUS 10 - MAY - 91 (130) 20: 52: 27.3 42 .534 N 43 .986 E 10 G 4.7 167 274 2.46 0:32 P WESTERN CAUCASUS 14 - MAY - 91 (134) 09: 36: 25.4 * 42 .609 N 43 .579 E 10 G 3.8 161 291 2.62 0:37 P WESTERN CAUCASUS 15 - MAY - 91 (135) 14: 28: 50.1 42 .565 N 43 .349 E 14 D 4.9 157 294 2.64 0:36 P WESTERN CAUCASUS 21 - MAY - 91 (141) 17: 37: 38.8 42 .867 N 48 .028 E 10 G 5.0 221 410 3.69 0:49 P CASPIAN SEA 24 - MAY - 91 (144) 07: 59: 38.8 * 42 .679 N 42 .908 E 10 G 3.9 152 321 2.89 0:26 P WESTERN CAUCASUS 27 - MAY - 91 (147) 03: 40: 45.5 ? 42 .34 N 45 .86 E 10 G 3.7 201 263 2.37 0:26 P EASTERN CAUCASUS 03 - JUN - 91 (154) 10: 22: 40.4 40 .048 N 42 .859 E 28 D 5.0 87 159 1.43 0:13 P TURKEY 04 - JUN - 91 (155) 00: 55: 16.3 40 .600 N 42 .989 E 10 G 3.7 110 156 1.40 0:16 P TURKEY 08 - JUN - 91 (159) 01: 12: 01.8 * 41 .005 N 43 .563 E 33 N 4.2 135 138 1.24 0:12 P TURKEY-USSR BORDER REGION 15 - JUN - 91 (166) 00: 59: 20.3 42 .461 N 44 .009 E 9 G 6.3 167 266 2.39 0:33 P WESTERN CAUCASUS 16 - JUN - 91 (167) 11: 07: 10.6 39 .984 N 42 .875 E 26 D 4.6 85 158 1.42 0:15 P TURKEY 17 - JUN - 91 (168) 03: 04: 45.5 * 42 .252 N 44 .222 E 10 G 4.4 170 239 2.15 0:32 P WESTERN CAUCASUS 19 - JUN - 91 (170) 06: 40: 28.9 40 .282 N 42 .971 E 33 N 4.6 97 150 1.35 0:21 P TURKEY 30 - JUN - 91 (181) 20: 09: 18.3 42 .424 N 43 .688 E 10 G 4.5 162 269 2.42 0:47 P WESTERN CAUCASUS 04 - JUL - 91 (185) 06: 26: 31.8 42 .387 N 44 .116 E 20 D 5.0 169 256 2.30 0:39 P WESTERN CAUCASUS 14 - JUL - 91 (195) 09: 09: 11.9 36 .334 N 71 .119 E 213 G 6.4 272 2335 21.00 4:32 P AFGHANISTAN-USSR BORDER REGION 10 - AUG - 91 (222) 08: 57: 51.8 * 40 .052 N 42 .153 E 10 G 4.4 88 219 1.97 0:46 P TURKEY 20 - AUG - 91 (232) 08: 46: 40.5 37 .646 N 72 .150 E 135 D 5.2 268 2380 21.40 4:43 P TAJIK SSR 05 - SEP - 91 (248) 19: 23: 04.8 38 .847 N 41 .417 E 10 G 4.3 64 318 2.86 0:48 P TURKEY 08 - SEP - 91 (251) 10: 14: 58.8 36 .264 N 71 .324 E 133 5.0 272 2355 21.17 4:43 P AFGHANISTAN-TAJIKISTAN BORD REG 06 - OCT - 91 (279) 01: 46: 47.5 41 .096 N 43 .409 E 18 D 5.0 134 154 1.39 0:24 P GEORGIA-ARMENIA-TURKEY BORD REG 08 - OCT - 91 (281) 03: 31: 15.6 45 .587 N 149 .049 E 146 D 6.0 226 7878 70.84 11:07 P KURIL ISLANDS 10 - OCT - 91 (283) 02: 44: 49.6 41 .399 N 43 .259 E 10 G 4.4 139 187 1.68 0:21 P GEORGIA-ARMENIA-TURKEY BORD REG 12 - NOV - 91 (316) 20: 35: 59.6 * 39 .306 N 44 .936 E 33 N 4.3 349 94 0.84 0:26 P ARMENIA-AZERBAIJAN-IRAN BORD REG 13 - NOV - 91 (317) 11: 12: 13.2 8 .361 N 126 .371 E 36 G 6.6 269 8701 78.24 12:01 P "MINDANAO, PHILIPPINE ISLANDS" 21 - NOV - 91 (325) 12: 38: 28.5 5 .782 N 126 .832 E 73 G 6.1 271 8923 80.24 12:10 P "MINDANAO, PHILIPPINE ISLANDS" 28 - NOV - 91 (332) 17: 19: 55.5 36 .924 N 49 .603 E 16 D 5.6 309 554 4.99 1:34 P WESTERN IRAN Date D.o.Y. Hr Mn Sec Latitude Longitude Depth Mag Azi Epicentral Distance Travel Phase Region deg. deg. km deg. km deg. m:ss 01 - DEC - 91 (335) 09: 17: 27.0 36 .373 N 45 .036 E 35 * 4.7 356 419 3.77 1:08 P IRAN-IRAQ BORDER REGION 07 - DEC - 91 (341) 11: 59: 00.9 45 .475 N 151 .391 E 50 D 6.0 225 8027 72.19 11:25 P KURIL ISLANDS 07 - DEC - 91 (341) 14: 22: 32.2 25 .191 N 62 .974 E 30 D 5.2 309 2374 21.35 4:51 P SOUTHWESTERN PAKISTAN 08 - DEC - 91 (342) 01: 02: 06.2 * 38 .335 N 48 .151 E 33 N 3.8 303 357 3.21 1:02 P ARMENIA-AZERBAIJAN-IRAN BORD REG 13 - DEC - 91 (347) 05: 45: 29.0 45 .567 N 151 .530 E 26 G 6.0 225 8029 72.20 11:30 P KURIL ISLANDS <2 events> 13 - DEC - 91 (347) 18: 59: 06.5 45 .521 N 151 .707 E 19 G 6.5 225 8043 72.33 11:32 P KURIL ISLANDS 13 - DEC - 91 (347) 19: 55: 09.5 45 .435 N 151 .270 E 48 D 6.4 225 8023 72.15 11:29 P KURIL ISLANDS 13 - DEC - 91 (347) 19: 58: 18.5 45 .439 N 151 .427 E 20 G 6.4 225 8032 72.23 11:32 P KURIL ISLANDS 19 - DEC - 91 (353) 01: 33: 40.4 45 .253 N 151 .176 E 27 G 6.6 225 8030 72.21 11:28 P KURIL ISLANDS 20 - DEC - 91 (354) 08: 35: 37.3 45 .133 N 151 .248 E 48 D 6.0 225 8043 72.33 11:28 P KURIL ISLANDS 22 - DEC - 91 (356) 08: 43: 13.4 45 .533 N 151 .021 E 25 D 7.5 225 8001 71.95 11:28 P KURIL ISLANDS 23 - DEC - 91 (357) 13: 10: 04.9 45 .854 N 151 .962 E 24 D 6.0 224 8034 72.25 11:30 P KURIL ISLANDS 26 - DEC - 91 (360) 11: 35: 56.2 54 .382 N 162 .521 E 29 D 5.5 213 7957 71.55 11:24 P NEAR EAST COAST OF KAMCHATKA 27 - DEC - 91 (361) 09: 09: 37.5 51 .019 N 98 .150 E 14 D 6.5 235 4229 38.03 7:31 P RUSSIA-MONGOLIA BORDER REGION 15 - FEB - 92 (046) 12: 52: 51.7 * 42 .803 N 46 .524 E 15 D 4.9 206 332 2.99 0:52 P EASTERN CAUCASUS 15 - FEB - 92 (046) 13: 30: 32.0 * 42 .462 N 46 .493 E 33 N 4.0 209 298 2.68 0:54 P EASTERN CAUCASUS 15 - FEB - 92 (046) 13: 37: 40.1 42 .934 N 46 .548 E 33 N 4.2 205 346 3.11 0:49 P EASTERN CAUCASUS 15 - FEB - 92 (046) 15: 18: 04.2 * 41 .434 N 46 .184 E 33 N 4.2 220 190 1.71 0:34 P EASTERN CAUCASUS 18 - FEB - 92 (049) 01: 39: 40.9 * 41 .477 N 43 .464 E 33 N 4.5 145 183 1.65 0:24 P GEORGIA-ARMENIA-TURKEY BORD REG 23 - FEB - 92 (054) 12: 03: 11.7 * 36 .391 N 49 .179 E 10 G 4.5 316 569 5.12 1:41 P WESTERN IRAN 26 - FEB - 92 (057) 03: 45: 19.7 11 .803 N 57 .764 E 10 G 5.8 334 3400 30.58 6:18 P ARABIAN SEA 02 - MAR - 92 (062) 12: 29: 40.2 52 .884 N 159 .997 E 44 D 6.9 215 7952 71.51 11:22 P NEAR EAST COAST OF KAMCHATKA 03 - MAR - 92 (063) 01: 18: 32.7 14 .265 S 167 .106 E 159 D 5.9 260 13761 123.75 18:44 PKP VANUATU ISLANDS 05 - MAR - 92 (065) 03: 30: 16.1 38 .263 N 44 .974 E 33 N 4.4 354 209 1.88 0:31 P TURKEY-IRAN BORDER REGION 13 - MAR - 92 (073) 17: 18: 40.1 39 .706 N 39 .570 E 28 D 7.1 85 442 3.98 1:04 P TURKEY 27 - MAR - 92 (087) 19: 21: 04.6 42 .456 N 43 .715 E 33 N 5.0 162 272 2.44 0:42 P NORTHWESTERN CAUCASUS 22 - APR - 92 (113) 03: 03: 47.6 * 39 .557 N 39 .557 E 10 G 4.5 83 446 4.01 1:17 P TURKEY 24 - APR - 92 (115) 07: 07: 25.1 27 .552 N 66 .057 E 33 N 6.1 299 2406 21.63 4:55 P PAKISTAN 26 - APR - 92 (117) 13: 15: 51.2 * 37 .663 N 47 .104 E 33 N 3.8 322 343 3.09 0:56 P NORTHWESTERN IRAN 30 - APR - 92 (121) 11: 44: 38.6 35 .070 N 26 .709 E 17 D 5.7 76 1680 15.11 3:44 P CRETE 07 - MAY - 92 (128) 19: 15: 02.3 38 .677 N 40 .130 E 10 G 5.0 69 427 3.84 1:15 P TURKEY 10 - MAY - 92 (131) 04: 04: 32.8 37 .193 N 72 .936 E 33 N 5.9 269 2461 22.13 4:59 P TAJIKISTAN 15 - MAY - 92 (136) 08: 08: 02.9 41 .003 N 72 .409 E 48 * 6.2 259 2331 20.96 4:44 P KYRGYZSTAN 17 - MAY - 92 (138) 09: 49: 18.7 7 .260 N 126 .753 E 33 N 7.2 270 8811 79.24 12:07 P "MINDANAO, PHILIPPINE ISLANDS" 17 - MAY - 92 (138) 10: 15: 31.2 7 .169 N 126 .861 E 33 N 7.3 270 8827 79.38 12:08 P "MINDANAO, PHILIPPINE ISLANDS" 20 - MAY - 92 (141) 12: 20: 35.0 33 .324 N 71 .271 E 33 N 6.0 279 2473 22.24 5:00 P PAKISTAN 10 - AUG - 92 (223) 13: 42: 34.9 36 .053 N 69 .706 E 111 D 5.3 274 2225 20.01 4:30 P "HINDU KUSH REGION, AFGHANISTAN" Table 3-5a. NEIC Parameters of Identified Events Sorted by Distance. Date D.o.Y. Hr Mn Sec Latitude Longitude Depth Mag Azi Epicentral Distance Travel Phase Region deg. deg. km deg. km deg. m:ss 27 - MAR - 91 (086) 22: 17: 55.0 40 .443 N 45 .443 E 33 N 4.3 240 70 0.63 -0:08 P EASTERN CAUCASUS 27 - APR - 91 (117) 03: 31: 58.5 * 40 .093 N 43 .719 E 10 G 4.2 87 86 0.77 0:07 P TURKEY-USSR BORDER REGION 12 - NOV - 91 (316) 20: 35: 59.6 * 39 .306 N 44 .936 E 33 N 4.3 349 94 0.84 0:26 P ARMENIA-AZERBAIJAN-IRAN BORD REG 08 - JUN - 91 (159) 01: 12: 01.8 * 41 .005 N 43 .563 E 33 N 4.2 135 138 1.24 0:12 P TURKEY-USSR BORDER REGION 02 - MAY - 91 (122) 02: 07: 31.6 ? 41 .34 N 45 .17 E 10 G 4.3 196 139 1.25 0:45 P EASTERN CAUCASUS 19 - JUN - 91 (170) 06: 40: 28.9 40 .282 N 42 .971 E 33 N 4.6 97 150 1.35 0:21 P TURKEY 06 - OCT - 91 (279) 01: 46: 47.5 41 .096 N 43 .409 E 18 D 5.0 134 154 1.39 0:24 P GEORGIA-ARMENIA-TURKEY BORD REG 04 - JUN - 91 (155) 00: 55: 16.3 40 .600 N 42 .989 E 10 G 3.7 110 156 1.40 0:16 P TURKEY 16 - JUN - 91 (167) 11: 07: 10.6 39 .984 N 42 .875 E 26 D 4.6 85 158 1.42 0:15 P TURKEY 03 - JUN - 91 (154) 10: 22: 40.4 40 .048 N 42 .859 E 28 D 5.0 87 159 1.43 0:13 P TURKEY 16 - DEC - 90 (350) 15: 45: 40.7 41 .361 N 43 .715 E 33 N 5.2 148 161 1.45 0:21 P TURKEY-USSR BORDER REGION 18 - FEB - 92 (049) 01: 39: 40.9 * 41 .477 N 43 .464 E 33 N 4.5 145 183 1.65 0:24 P GEORGIA-ARMENIA-TURKEY BORD REG 10 - OCT - 91 (283) 02: 44: 49.6 41 .399 N 43 .259 E 10 G 4.4 139 187 1.68 0:21 P GEORGIA-ARMENIA-TURKEY BORD REG 15 - FEB - 92 (046) 15: 18: 04.2 * 41 .434 N 46 .184 E 33 N 4.2 220 190 1.71 0:34 P EASTERN CAUCASUS 05 - MAR - 92 (065) 03: 30: 16.1 38 .263 N 44 .974 E 33 N 4.4 354 209 1.88 0:31 P TURKEY-IRAN BORDER REGION 03 - MAY - 91 (123) 06: 12: 54.2 ? 41 .93 N 43 .80 E 33 N 4.2 159 214 1.93 0:41 P TURKEY-USSR BORDER REGION 10 - AUG - 91 (222) 08: 57: 51.8 * 40 .052 N 42 .153 E 10 G 4.4 88 219 1.97 0:46 P TURKEY 23 - DEC - 90 (357) 21: 28: 50.7 * 42 .115 N 44 .356 E 33 N 4.1 172 222 2.00 0:23 P WESTERN CAUCASUS 17 - JUN - 91 (168) 03: 04: 45.5 * 42 .252 N 44 .222 E 10 G 4.4 170 239 2.15 0:32 P WESTERN CAUCASUS 02 - MAY - 91 (122) 02: 18: 00.1 * 42 .211 N 43 .906 E 10 G 4.1 164 241 2.17 0:32 P WESTERN CAUCASUS 04 - MAY - 91 (124) 04: 53: 35.6 ? 42 .15 N 43 .51 E 10 G 4.2 156 246 2.21 0:41 P WESTERN CAUCASUS 04 - JUL - 91 (185) 06: 26: 31.8 42 .387 N 44 .116 E 20 D 5.0 169 256 2.30 0:39 P WESTERN CAUCASUS 27 - MAY - 91 (147) 03: 40: 45.5 ? 42 .34 N 45 .86 E 10 G 3.7 201 263 2.37 0:26 P EASTERN CAUCASUS 15 - JUN - 91 (166) 00: 59: 20.3 42 .461 N 44 .009 E 9 G 6.3 167 266 2.39 0:33 P WESTERN CAUCASUS 30 - JUN - 91 (181) 20: 09: 18.3 42 .424 N 43 .688 E 10 G 4.5 162 269 2.42 0:47 P WESTERN CAUCASUS 27 - MAR - 92 (087) 19: 21: 04.6 42 .456 N 43 .715 E 33 N 5.0 162 272 2.44 0:42 P NORTHWESTERN CAUCASUS 29 - APR - 91 (119) 18: 30: 41.5 42 .503 N 43 .899 E 14 G 6.0 166 272 2.45 0:36 P WESTERN CAUCASUS 29 - APR - 91 (119) 09: 12: 48.1 42 .453 N 43 .673 E 17 G 7.2 162 272 2.45 0:29 P WESTERN CAUCASUS 29 - APR - 91 (119) 14: 43: 06.3 42 .515 N 43 .937 E 10 G 5.4 166 273 2.45 0:35 P WESTERN CAUCASUS 10 - MAY - 91 (130) 20: 52: 27.3 42 .534 N 43 .986 E 10 G 4.7 167 274 2.46 0:32 P WESTERN CAUCASUS 29 - APR - 91 (119) 11: 04: 28.9 * 42 .510 N 43 .816 E 10 G 4.3 164 275 2.47 0:35 P WESTERN CAUCASUS 02 - MAY - 91 (122) 01: 25: 30.1 42 .541 N 43 .960 E 10 G 5.1 167 275 2.47 0:32 P WESTERN CAUCASUS 20 - JUL - 90 (201) 17: 30: 36.2 ? 42 .10 N 46 .77 E 33 N 4.2 217 278 2.50 0:50 P EASTERN CAUCASUS 29 - APR - 91 (119) 11: 10: 11.9 42 .584 N 43 .904 E 10 G 4.7 166 281 2.53 0:35 P WESTERN CAUCASUS 29 - APR - 91 (119) 11: 51: 10.3 42 .572 N 43 .816 E 10 G 4.9 165 281 2.53 0:34 P WESTERN CAUCASUS 02 - MAY - 91 (122) 09: 44: 41.4 42 .507 N 43 .507 E 10 G 4.5 159 283 2.54 0:36 P WESTERN CAUCASUS 29 - APR - 91 (119) 18: 23: 15.2 42 .583 N 43 .764 E 10 G 5.5 164 284 2.55 0:35 P WESTERN CAUCASUS 29 - APR - 91 (119) 11: 59: 54.8 42 .625 N 43 .962 E 10 G 4.5 167 284 2.56 0:34 P WESTERN CAUCASUS 03 - MAY - 91 (123) 06: 08: 37.1 42 .482 N 43 .363 E 10 G 4.6 157 285 2.56 0:37 P WESTERN CAUCASUS 02 - MAY - 91 (122) 04: 30: 53.9 * 42 .481 N 43 .201 E 10 G 3.9 155 290 2.61 0:41 P WESTERN CAUCASUS 29 - APR - 91 (119) 10: 52: 42.2 42 .712 N 44 .102 E 10 G 4.6 170 291 2.62 0:32 P WESTERN CAUCASUS 14 - MAY - 91 (134) 09: 36: 25.4 * 42 .609 N 43 .579 E 10 G 3.8 161 291 2.62 0:37 P WESTERN CAUCASUS 01 - MAY - 91 (121) 23: 19: 11.8 * 42 .719 N 44 .053 E 10 G 4.1 169 293 2.63 0:29 P WESTERN CAUCASUS 10 - MAY - 91 (130) 01: 25: 15.6 42 .496 N 43 .153 E 10 G 4.6 154 294 2.64 0:40 P WESTERN CAUCASUS 15 - MAY - 91 (135) 14: 28: 50.1 42 .565 N 43 .349 E 14 D 4.9 157 294 2.64 0:36 P WESTERN CAUCASUS 02 - MAY - 91 (122) 03: 42: 26.1 * 42 .608 N 43 .477 E 10 G 4.0 160 294 2.64 0:42 P WESTERN CAUCASUS 10 - MAY - 91 (130) 20: 30: 45.3 42 .627 N 43 .449 E 28 D 4.4 159 297 2.67 0:35 P WESTERN CAUCASUS 15 - FEB - 92 (046) 13: 30: 32.0 * 42 .462 N 46 .493 E 33 N 4.0 209 298 2.68 0:54 P EASTERN CAUCASUS 02 - MAY - 91 (122) 09: 00: 35.2 * 42 .704 N 43 .692 E 10 G 4.1 164 298 2.68 0:33 P WESTERN CAUCASUS 22 - SEP - 90 (265) 02: 46: 01.2 * 42 .538 N 46 .449 E 33 N 4.3 208 304 2.73 0:34 P EASTERN CAUCASUS 03 - MAY - 91 (123) 23: 41: 01.8 42 .647 N 43 .263 E 11 D 5.2 157 305 2.74 0:39 P WESTERN CAUCASUS 23 - JUL - 90 (204) 20: 54: 56.6 42 .719 N 45 .947 E 33 N 4.8 199 305 2.74 0:47 Pn EASTERN CAUCASUS 07 - MAY - 91 (127) 09: 01: 23.6 * 42 .606 N 43 .125 E 10 G 4.2 155 306 2.75 0:38 P WESTERN CAUCASUS 03 - MAY - 91 (123) 20: 19: 38.8 42 .683 N 43 .247 E 10 G 5.3 157 309 2.78 0:38 P WESTERN CAUCASUS 05 - SEP - 91 (248) 19: 23: 04.8 38 .847 N 41 .417 E 10 G 4.3 64 318 2.86 0:48 P TURKEY 01 - JAN - 91 (001) 19: 18: 56.4 39 .822 N 48 .439 E 61 D 4.9 275 318 2.86 0:48 P N.W. IRAN-USSR BORDER REGION 24 - MAY - 91 (144) 07: 59: 38.8 * 42 .679 N 42 .908 E 10 G 3.9 152 321 2.89 0:26 P WESTERN CAUCASUS 15 - FEB - 92 (046) 12: 52: 51.7 * 42 .803 N 46 .524 E 15 D 4.9 206 332 2.99 0:52 P EASTERN CAUCASUS 26 - APR - 92 (117) 13: 15: 51.2 * 37 .663 N 47 .104 E 33 N 3.8 322 343 3.09 0:56 P NORTHWESTERN IRAN 15 - FEB - 92 (046) 13: 37: 40.1 42 .934 N 46 .548 E 33 N 4.2 205 346 3.11 0:49 P EASTERN CAUCASUS 02 - AUG - 90 (214) 17: 12: 48.5 * 38 .540 N 48 .186 E 33 N 4.2 300 346 3.12 0:56 P N.W. IRAN-USSR BORDER REGION 24 - SEP - 90 (267) 06: 35: 13.9 * 38 .253 N 47 .951 E 10 G 4.6 306 348 3.13 P NORTHWESTERN IRAN 08 - DEC - 91 (342) 01: 02: 06.2 * 38 .335 N 48 .151 E 33 N 3.8 303 357 3.21 1:02 P ARMENIA-AZERBAIJAN-IRAN BORD REG 02 - AUG - 90 (214) 21: 17: 18.7 * 38 .398 N 48 .228 E 33 N 4.1 301 358 3.22 0:55 P N.W. IRAN-USSR BORDER REGION 21 - MAY - 91 (141) 17: 37: 38.8 42 .867 N 48 .028 E 10 G 5.0 221 410 3.69 0:49 P CASPIAN SEA 01 - DEC - 91 (335) 09: 17: 27.0 36 .373 N 45 .036 E 35 * 4.7 356 419 3.77 1:08 P IRAN-IRAQ BORDER REGION 07 - MAY - 92 (128) 19: 15: 02.3 38 .677 N 40 .130 E 10 G 5.0 69 427 3.84 1:15 P TURKEY 13 - MAR - 92 (073) 17: 18: 40.1 39 .706 N 39 .570 E 28 D 7.1 85 442 3.98 1:04 P TURKEY 22 - APR - 92 (113) 03: 03: 47.6 * 39 .557 N 39 .557 E 10 G 4.5 83 446 4.01 1:17 P TURKEY 01 - JUL - 90 (182) 21: 16: 48.3 37 .285 N 48 .820 E 10 G 4.7 310 476 4.28 1:29 P CASPIAN SEA 01 - JUL - 90 (182) 17: 19: 44.1 37 .280 N 48 .818 E 10 G 4.6 310 476 4.28 1:30 P CASPIAN SEA 28 - DEC - 90 (362) 04: 03: 53.6 37 .106 N 49 .227 E 10 G 5.0 309 516 4.64 1:29 P CASPIAN SEA 27 - JUL - 90 (208) 05: 31: 00.1 37 .318 N 49 .585 E 10 G 4.8 305 525 4.72 1:29 P CASPIAN SEA 22 - AUG - 90 (234) 07: 51: 49.5 * 37 .056 N 49 .327 E 10 G 4.3 309 526 4.73 1:33 P CASPIAN SEA 21 - AUG - 90 (233) 03: 47: 26.2 37 .309 N 49 .685 E 10 G 4.8 305 533 4.79 1:30 P CASPIAN SEA 06 - JUL - 90 (187) 19: 34: 52.4 36 .861 N 49 .303 E 35 D 5.3 311 540 4.85 1:16 Pn WESTERN IRAN 27 - DEC - 90 (361) 13: 26: 57.1 36 .539 N 48 .907 E 10 G 4.7 316 541 4.87 1:26 P NORTHWESTERN IRAN 11 - JUL - 90 (192) 04: 36: 08.6 * 37 .015 N 49 .530 E 33 N 4.5 308 543 4.88 1:35 P CASPIAN SEA 28 - JUN - 90 (179) 03: 20: 35.0 37 .085 N 49 .642 E 10 G 4.8 307 545 4.90 1:36 P CASPIAN SEA 28 - NOV - 91 (332) 17: 19: 55.5 36 .924 N 49 .603 E 16 D 5.6 309 554 4.99 1:34 P WESTERN IRAN 01 - JUL - 90 (182) 12: 24: 57.2 37 .181 N 49 .885 E 10 G 4.8 305 555 4.99 1:35 P CASPIAN SEA 20 - AUG - 90 (232) 12: 20: 11.0 * 36 .956 N 49 .720 E 33 N 4.8 308 560 5.03 1:30 P WESTERN IRAN 17 - JUL - 90 (198) 04: 02: 09.2 37 .137 N 49 .979 E 33 N 4.6 304 565 5.08 1:35 P CASPIAN SEA 23 - FEB - 92 (054) 12: 03: 11.7 * 36 .391 N 49 .179 E 10 G 4.5 316 569 5.12 1:41 P WESTERN IRAN 28 - JUN - 90 (179) 03: 42: 01.9 * 37 .079 N 50 .147 E 10 G 4.7 304 581 5.22 1:39 P CASPIAN SEA 13 - AUG - 90 (225) 06: 18: 25.1 36 .663 N 49 .884 E 35 * 4.6 309 592 5.33 1:37 P WESTERN IRAN 18 - JUL - 90 (199) 11: 29: 24.9 36 .990 N 29 .595 E 17 D 5.2 80 1359 12.22 3:07 P TURKEY 30 - APR - 92 (121) 11: 44: 38.6 35 .070 N 26 .709 E 17 D 5.7 76 1680 15.11 3:44 P CRETE 10 - AUG - 92 (223) 13: 42: 34.9 36 .053 N 69 .706 E 111 D 5.3 274 2225 20.01 4:30 P "HINDU KUSH REGION, AFGHANISTAN" 31 - JAN - 91 (031) 23: 03: 33.6 35 .993 N 70 .423 E 142 G 6.7 273 2288 20.57 4:31 P HINDU KUSH REGION 03 - SEP - 90 (246) 02: 40: 59.1 36 .409 N 70 .671 E 202 D 4.9 272 2294 20.63 4:27 P HINDU KUSH REGION 13 - JUL - 90 (194) 14: 20: 43.4 36 .415 N 70 .789 E 217 D 5.6 272 2304 20.72 4:28 P HINDU KUSH REGION 25 - OCT - 90 (298) 04: 53: 59.9 35 .121 N 70 .486 E 114 G 6.0 276 2327 20.93 4:38 P HINDU KUSH REGION 15 - MAY - 92 (136) 08: 08: 02.9 41 .003 N 72 .409 E 48 * 6.2 259 2331 20.96 4:44 P KYRGYZSTAN 14 - JUL - 91 (195) 09: 09: 11.9 36 .334 N 71 .119 E 213 G 6.4 272 2335 21.00 4:32 P AFGHANISTAN-USSR BORDER REGION 08 - SEP - 91 (251) 10: 14: 58.8 36 .264 N 71 .324 E 133 5.0 272 2355 21.17 4:43 P AFGHANISTAN-TAJIKISTAN BORD REG 15 - APR - 91 (105) 10: 48: 59.3 36 .340 N 71 .358 E 124 D 5.3 272 2355 21.18 4:30 P AFGHANISTAN-USSR BORDER REGION 07 - DEC - 91 (341) 14: 22: 32.2 25 .191 N 62 .974 E 30 D 5.2 309 2374 21.35 4:51 P SOUTHWESTERN PAKISTAN 20 - AUG - 91 (232) 08: 46: 40.5 37 .646 N 72 .150 E 135 D 5.2 268 2380 21.40 4:43 P TAJIK SSR 26 - JUL - 90 (207) 06: 53: 56.3 27 .247 N 65 .508 E 19 G 5.8 300 2388 21.47 4:51 P PAKISTAN <2 events> 24 - APR - 92 (115) 07: 07: 25.1 27 .552 N 66 .057 E 33 N 6.1 299 2406 21.63 4:55 P PAKISTAN 08 - SEP - 90 (251) 19: 33: 18.8 27 .500 N 66 .092 E 28 * 5.5 299 2412 21.69 4:52 P PAKISTAN 14 - AUG - 90 (226) 00: 50: 39.2 27 .024 N 65 .969 E 21 D 5.2 300 2438 21.93 4:56 P PAKISTAN 10 - MAY - 92 (131) 04: 04: 32.8 37 .193 N 72 .936 E 33 N 5.9 269 2461 22.13 4:59 P TAJIKISTAN 20 - MAY - 92 (141) 12: 20: 35.0 33 .324 N 71 .271 E 33 N 6.0 279 2473 22.24 5:00 P PAKISTAN 26 - FEB - 91 (057) 07: 25: 47.2 40 .186 N 13 .822 E 401 5.5 100 2613 23.49 4:30 P TYRRHENIAN SEA 12 - NOV - 90 (316) 12: 28: 51.5 42 .959 N 78 .071 E 19 G 6.3 252 2774 24.95 5:28 P ALMA-ATA REGION 14 - SEP - 90 (257) 20: 40: 18.3 13 .382 N 51 .456 E 10 G 5.4 346 3046 27.39 5:50 P EASTERN GULF OF ADEN 03 - AUG - 90 (215) 09: 15: 06.1 47 .963 N 84 .961 E 33 G 6.1 241 3291 29.59 6:05 P KAZAKH-XINJIANG BORDER REGION 26 - FEB - 92 (057) 03: 45: 19.7 11 .803 N 57 .764 E 10 G 5.8 334 3400 30.58 6:18 P ARABIAN SEA 16 - AUG - 90 (228) 04: 59: 57.6 41 .564 N 88 .770 E 0 G 6.2 253 3668 32.98 6:39 P "SOUTHERN XINJIANG, CHINA" 10 - AUG - 90 (222) 21: 11: 49.0 6 .572 N 60 .240 E 10 G 5.5 333 4040 36.33 7:07 P CARLSBERG RIDGE 07 - SEP - 90 (250) 00: 12: 26.2 5 .443 N 31 .686 E 10 G 5.2 22 4072 36.62 7:09 P SUDAN 09 - JUL - 90 (190) 15: 11: 20.3 5 .395 N 31 .654 E 13 G 6.4 22 4078 36.67 7:09 P SUDAN 27 - DEC - 91 (361) 09: 09: 37.5 51 .019 N 98 .150 E 14 D 6.5 235 4229 38.03 7:31 P RUSSIA-MONGOLIA BORDER REGION 25 - OCT - 90 (298) 04: 52: 06.0 * 76 .243 N 8 .409 E 10 G 4.6 167 4382 39.41 ?7:47 P SVALBARD REGION 09 - SEP - 90 (252) 02: 14: 51.0 56 .654 N 34 .395 W 10 G 5.4 137 5765 51.84 9:14 P NORTH ATLANTIC OCEAN 29 - AUG - 90 (241) 20: 44: 23.0 11 .791 N 95 .034 E 25 D 5.2 288 5830 52.43 9:15 P ANDAMAN ISLANDS REGION 14 - AUG - 90 (226) 15: 13: 28.6 35 .432 N 35 .648 W 10 G 6.0 114 6833 61.45 10:27 P NORTH ATLANTIC RIDGE 04 - JUL - 90 (185) 02: 24: 41.9 25 .372 N 124 .473 E 133 5.6 256 7392 66.47 10:38 P NORTHEAST OF TAIWAN 14 - APR - 91 (104) 08: 08: 55.7 27 .155 N 127 .419 E 83 G 6.2 253 7519 67.62 10:45 P RYUKYU ISLANDS 15 - AUG - 90 (227) 23: 08: 56.0 43 .757 N 143 .297 E 162 D 5.4 230 7637 68.68 10:51 P "HOKKAIDO, JAPAN REGION" 16 - JUL - 90 (197) 13: 31: 13.2 16 .285 N 120 .457 E 13 D 5.7 266 7650 68.79 11:04 P "LUZON, PHILIPPINE ISLANDS" 16 - JUL - 90 (197) 19: 45: 25.1 16 .365 N 120 .546 E 33 N 5.4 266 7652 68.81 11:04 P "LUZON, PHILIPPINE ISLANDS" 14 - JUL - 90 (195) 05: 54: 25.4 0 .003 N 17 .376 W 11 G 6.4 71 7676 69.03 11:07 P NORTH OF ASCENCION ISLAND 17 - JUL - 90 (198) 21: 14: 43.8 16 .495 N 120 .981 E 23 G 6.7 266 7680 69.07 11:09 P "LUZON, PHILIPPINE ISLANDS" 18 - JUL - 90 (199) 08: 00: 12.8 16 .511 N 121 .007 E 14 G 5.8 266 7681 69.08 11:10 P "LUZON, PHILIPPINE ISLANDS" 22 - JUL - 90 (203) 11: 20: 09.6 16 .532 N 121 .045 E 33 N 5.3 266 7683 69.09 11:07 P "LUZON, PHILIPPINE ISLANDS" 14 - JUL - 90 (195) 07: 24: 39.6 0 .074 S 17 .523 W 12 G 5.8 71 7694 69.19 11:10 P NORTH OF ASCENCION ISLAND 16 - JUL - 90 (197) 07: 26: 34.6 15 .679 N 121 .172 E 25 D 7.9 266 7752 69.71 11:12 P "LUZON, PHILIPPINE ISLANDS" 08 - OCT - 91 (281) 03: 31: 15.6 45 .587 N 149 .049 E 146 D 6.0 226 7878 70.84 11:07 P KURIL ISLANDS 17 - SEP - 90 (260) 11: 57: 24.1 5 .917 S 103 .796 E 59 D 5.7 296 7902 71.06 11:14 P SOUTHERN SUMATERA 02 - MAR - 92 (062) 12: 29: 40.2 52 .884 N 159 .997 E 44 D 6.9 215 7952 71.51 11:22 P NEAR EAST COAST OF KAMCHATKA 26 - DEC - 91 (360) 11: 35: 56.2 54 .382 N 162 .521 E 29 D 5.5 213 7957 71.55 11:24 P NEAR EAST COAST OF KAMCHATKA 06 - JUL - 90 (187) 05: 02: 27.9 45 .371 N 150 .170 E 42 D 5.7 226 7961 71.59 11:22 P KURIL ISLANDS 22 - DEC - 91 (356) 08: 43: 13.4 45 .533 N 151 .021 E 25 D 7.5 225 8001 71.95 11:28 P KURIL ISLANDS 13 - DEC - 91 (347) 19: 55: 09.5 45 .435 N 151 .270 E 48 D 6.4 225 8023 72.15 11:29 P KURIL ISLANDS 07 - DEC - 91 (341) 11: 59: 00.9 45 .475 N 151 .391 E 50 D 6.0 225 8027 72.19 11:25 P KURIL ISLANDS 13 - DEC - 91 (347) 05: 45: 29.0 45 .567 N 151 .530 E 26 G 6.0 225 8029 72.20 11:30 P KURIL ISLANDS <2 events> 19 - DEC - 91 (353) 01: 33: 40.4 45 .253 N 151 .176 E 27 G 6.6 225 8030 72.21 11:28 P KURIL ISLANDS 13 - DEC - 91 (347) 19: 58: 18.5 45 .439 N 151 .427 E 20 G 6.4 225 8032 72.23 11:32 P KURIL ISLANDS 23 - DEC - 91 (357) 13: 10: 04.9 45 .854 N 151 .962 E 24 D 6.0 224 8034 72.25 11:30 P KURIL ISLANDS 13 - DEC - 91 (347) 18: 59: 06.5 45 .521 N 151 .707 E 19 G 6.5 225 8043 72.33 11:32 P KURIL ISLANDS 20 - DEC - 91 (354) 08: 35: 37.3 45 .133 N 151 .248 E 48 D 6.0 225 8043 72.33 11:28 P KURIL ISLANDS 13 - NOV - 91 (317) 11: 12: 13.2 8 .361 N 126 .371 E 36 G 6.6 269 8701 78.24 12:01 P "MINDANAO, PHILIPPINE ISLANDS" 17 - MAY - 92 (138) 09: 49: 18.7 7 .260 N 126 .753 E 33 N 7.2 270 8811 79.24 12:07 P "MINDANAO, PHILIPPINE ISLANDS" 17 - MAY - 92 (138) 10: 15: 31.2 7 .169 N 126 .861 E 33 N 7.3 270 8827 79.38 12:08 P "MINDANAO, PHILIPPINE ISLANDS" 21 - NOV - 91 (325) 12: 38: 28.5 5 .782 N 126 .832 E 73 G 6.1 271 8923 80.24 12:10 P "MINDANAO, PHILIPPINE ISLANDS" 25 - AUG - 90 (237) 15: 47: 53.8 0 .525 N 126 .084 E 11 G 6.5 275 9236 83.06 12:29 P MOLUCCA PASSAGE 10 - AUG - 90 (222) 15: 44: 31.3 0 .333 N 126 .175 E 53 6.4 275 9258 83.25 12:25 P MOLUCCA PASSAGE 03 - MAR - 92 (063) 01: 18: 32.7 14 .265 S 167 .106 E 159 D 5.9 260 13761 123.75 18:44 PKP VANUATU ISLANDS 27 - JUL - 90 (208) 12: 37: 59.5 15 .355 S 167 .464 E 126 G 7.5 261 13866 124.70 18:48 PKP VANUATU ISLANDS 12 - AUG - 90 (224) 21: 25: 21.9 19 .435 S 169 .132 E 140 G 6.3 263 14283 128.44 18:52 PKP VANUATU ISLANDS <2 events> 22 - JUL - 90 (203) 09: 26: 14.6 23 .622 S 179 .893 W 531 G 5.9 260 15477 139.18 21:14 SKP SOUTH OF FIJI ISLANDS Table 3-5a. NEIC Parameters of Identified Events Sorted by Magnitude. Date D.o.Y. Hr Mn Sec Latitude Longitude Depth Mag Azi Epicentral Distance Travel Phase Region deg. deg. km deg. km deg. m:ss 16 - JUL - 90 (197) 07: 26: 34.6 15 .679 N 121 .172 E 25 D 7.9 266 7752 69.71 11:12 P "LUZON, PHILIPPINE ISLANDS" 22 - DEC - 91 (356) 08: 43: 13.4 45 .533 N 151 .021 E 25 D 7.5 225 8001 71.95 11:28 P KURIL ISLANDS 27 - JUL - 90 (208) 12: 37: 59.5 15 .355 S 167 .464 E 126 G 7.5 261 13866 124.70 18:48 PKP VANUATU ISLANDS 17 - MAY - 92 (138) 10: 15: 31.2 7 .169 N 126 .861 E 33 N 7.3 270 8827 79.38 12:08 P "MINDANAO, PHILIPPINE ISLANDS" 29 - APR - 91 (119) 09: 12: 48.1 42 .453 N 43 .673 E 17 G 7.2 162 272 2.45 0:29 P WESTERN CAUCASUS 17 - MAY - 92 (138) 09: 49: 18.7 7 .260 N 126 .753 E 33 N 7.2 270 8811 79.24 12:07 P "MINDANAO, PHILIPPINE ISLANDS" 13 - MAR - 92 (073) 17: 18: 40.1 39 .706 N 39 .570 E 28 D 7.1 85 442 3.98 1:04 P TURKEY 02 - MAR - 92 (062) 12: 29: 40.2 52 .884 N 159 .997 E 44 D 6.9 215 7952 71.51 11:22 P NEAR EAST COAST OF KAMCHATKA 31 - JAN - 91 (031) 23: 03: 33.6 35 .993 N 70 .423 E 142 G 6.7 273 2288 20.57 4:31 P HINDU KUSH REGION 17 - JUL - 90 (198) 21: 14: 43.8 16 .495 N 120 .981 E 23 G 6.7 266 7680 69.07 11:09 P "LUZON, PHILIPPINE ISLANDS" 19 - DEC - 91 (353) 01: 33: 40.4 45 .253 N 151 .176 E 27 G 6.6 225 8030 72.21 11:28 P KURIL ISLANDS 13 - NOV - 91 (317) 11: 12: 13.2 8 .361 N 126 .371 E 36 G 6.6 269 8701 78.24 12:01 P "MINDANAO, PHILIPPINE ISLANDS" 27 - DEC - 91 (361) 09: 09: 37.5 51 .019 N 98 .150 E 14 D 6.5 235 4229 38.03 7:31 P RUSSIA-MONGOLIA BORDER REGION 13 - DEC - 91 (347) 18: 59: 06.5 45 .521 N 151 .707 E 19 G 6.5 225 8043 72.33 11:32 P KURIL ISLANDS 25 - AUG - 90 (237) 15: 47: 53.8 0 .525 N 126 .084 E 11 G 6.5 275 9236 83.06 12:29 P MOLUCCA PASSAGE 14 - JUL - 91 (195) 09: 09: 11.9 36 .334 N 71 .119 E 213 G 6.4 272 2335 21.00 4:32 P AFGHANISTAN-USSR BORDER REGION 09 - JUL - 90 (190) 15: 11: 20.3 5 .395 N 31 .654 E 13 G 6.4 22 4078 36.67 7:09 P SUDAN 14 - JUL - 90 (195) 05: 54: 25.4 0 .003 N 17 .376 W 11 G 6.4 71 7676 69.03 11:07 P NORTH OF ASCENCION ISLAND 13 - DEC - 91 (347) 19: 55: 09.5 45 .435 N 151 .270 E 48 D 6.4 225 8023 72.15 11:29 P KURIL ISLANDS 13 - DEC - 91 (347) 19: 58: 18.5 45 .439 N 151 .427 E 20 G 6.4 225 8032 72.23 11:32 P KURIL ISLANDS 10 - AUG - 90 (222) 15: 44: 31.3 0 .333 N 126 .175 E 53 6.4 275 9258 83.25 12:25 P MOLUCCA PASSAGE 15 - JUN - 91 (166) 00: 59: 20.3 42 .461 N 44 .009 E 9 G 6.3 167 266 2.39 0:33 P WESTERN CAUCASUS 12 - NOV - 90 (316) 12: 28: 51.5 42 .959 N 78 .071 E 19 G 6.3 252 2774 24.95 5:28 P ALMA-ATA REGION 12 - AUG - 90 (224) 21: 25: 21.9 19 .435 S 169 .132 E 140 G 6.3 263 14283 128.44 18:52 PKP VANUATU ISLANDS <2 events> 15 - MAY - 92 (136) 08: 08: 02.9 41 .003 N 72 .409 E 48 * 6.2 259 2331 20.96 4:44 P KYRGYZSTAN 16 - AUG - 90 (228) 04: 59: 57.6 41 .564 N 88 .770 E 0 G 6.2 253 3668 32.98 6:39 P "SOUTHERN XINJIANG, CHINA" 14 - APR - 91 (104) 08: 08: 55.7 27 .155 N 127 .419 E 83 G 6.2 253 7519 67.62 10:45 P RYUKYU ISLANDS 24 - APR - 92 (115) 07: 07: 25.1 27 .552 N 66 .057 E 33 N 6.1 299 2406 21.63 4:55 P PAKISTAN 03 - AUG - 90 (215) 09: 15: 06.1 47 .963 N 84 .961 E 33 G 6.1 241 3291 29.59 6:05 P KAZAKH-XINJIANG BORDER REGION 21 - NOV - 91 (325) 12: 38: 28.5 5 .782 N 126 .832 E 73 G 6.1 271 8923 80.24 12:10 P "MINDANAO, PHILIPPINE ISLANDS" 29 - APR - 91 (119) 18: 30: 41.5 42 .503 N 43 .899 E 14 G 6.0 166 272 2.45 0:36 P WESTERN CAUCASUS 25 - OCT - 90 (298) 04: 53: 59.9 35 .121 N 70 .486 E 114 G 6.0 276 2327 20.93 4:38 P HINDU KUSH REGION 20 - MAY - 92 (141) 12: 20: 35.0 33 .324 N 71 .271 E 33 N 6.0 279 2473 22.24 5:00 P PAKISTAN 14 - AUG - 90 (226) 15: 13: 28.6 35 .432 N 35 .648 W 10 G 6.0 114 6833 61.45 10:27 P NORTH ATLANTIC RIDGE 08 - OCT - 91 (281) 03: 31: 15.6 45 .587 N 149 .049 E 146 D 6.0 226 7878 70.84 11:07 P KURIL ISLANDS 07 - DEC - 91 (341) 11: 59: 00.9 45 .475 N 151 .391 E 50 D 6.0 225 8027 72.19 11:25 P KURIL ISLANDS 13 - DEC - 91 (347) 05: 45: 29.0 45 .567 N 151 .530 E 26 G 6.0 225 8029 72.20 11:30 P KURIL ISLANDS <2 events> 23 - DEC - 91 (357) 13: 10: 04.9 45 .854 N 151 .962 E 24 D 6.0 224 8034 72.25 11:30 P KURIL ISLANDS 20 - DEC - 91 (354) 08: 35: 37.3 45 .133 N 151 .248 E 48 D 6.0 225 8043 72.33 11:28 P KURIL ISLANDS 10 - MAY - 92 (131) 04: 04: 32.8 37 .193 N 72 .936 E 33 N 5.9 269 2461 22.13 4:59 P TAJIKISTAN 03 - MAR - 92 (063) 01: 18: 32.7 14 .265 S 167 .106 E 159 D 5.9 260 13761 123.75 18:44 PKP VANUATU ISLANDS 22 - JUL - 90 (203) 09: 26: 14.6 23 .622 S 179 .893 W 531 G 5.9 260 15477 139.18 21:14 SKP SOUTH OF FIJI ISLANDS 26 - JUL - 90 (207) 06: 53: 56.3 27 .247 N 65 .508 E 19 G 5.8 300 2388 21.47 4:51 P PAKISTAN <2 events> 26 - FEB - 92 (057) 03: 45: 19.7 11 .803 N 57 .764 E 10 G 5.8 334 3400 30.58 6:18 P ARABIAN SEA 18 - JUL - 90 (199) 08: 00: 12.8 16 .511 N 121 .007 E 14 G 5.8 266 7681 69.08 11:10 P "LUZON, PHILIPPINE ISLANDS" 14 - JUL - 90 (195) 07: 24: 39.6 0 .074 S 17 .523 W 12 G 5.8 71 7694 69.19 11:10 P NORTH OF ASCENCION ISLAND 30 - APR - 92 (121) 11: 44: 38.6 35 .070 N 26 .709 E 17 D 5.7 76 1680 15.11 3:44 P CRETE 16 - JUL - 90 (197) 13: 31: 13.2 16 .285 N 120 .457 E 13 D 5.7 266 7650 68.79 11:04 P "LUZON, PHILIPPINE ISLANDS" 17 - SEP - 90 (260) 11: 57: 24.1 5 .917 S 103 .796 E 59 D 5.7 296 7902 71.06 11:14 P SOUTHERN SUMATERA 06 - JUL - 90 (187) 05: 02: 27.9 45 .371 N 150 .170 E 42 D 5.7 226 7961 71.59 11:22 P KURIL ISLANDS 28 - NOV - 91 (332) 17: 19: 55.5 36 .924 N 49 .603 E 16 D 5.6 309 554 4.99 1:34 P WESTERN IRAN 13 - JUL - 90 (194) 14: 20: 43.4 36 .415 N 70 .789 E 217 D 5.6 272 2304 20.72 4:28 P HINDU KUSH REGION 04 - JUL - 90 (185) 02: 24: 41.9 25 .372 N 124 .473 E 133 5.6 256 7392 66.47 10:38 P NORTHEAST OF TAIWAN 29 - APR - 91 (119) 18: 23: 15.2 42 .583 N 43 .764 E 10 G 5.5 164 284 2.55 0:35 P WESTERN CAUCASUS 08 - SEP - 90 (251) 19: 33: 18.8 27 .500 N 66 .092 E 28 * 5.5 299 2412 21.69 4:52 P PAKISTAN 26 - FEB - 91 (057) 07: 25: 47.2 40 .186 N 13 .822 E 401 5.5 100 2613 23.49 4:30 P TYRRHENIAN SEA 10 - AUG - 90 (222) 21: 11: 49.0 6 .572 N 60 .240 E 10 G 5.5 333 4040 36.33 7:07 P CARLSBERG RIDGE 26 - DEC - 91 (360) 11: 35: 56.2 54 .382 N 162 .521 E 29 D 5.5 213 7957 71.55 11:24 P NEAR EAST COAST OF KAMCHATKA 29 - APR - 91 (119) 14: 43: 06.3 42 .515 N 43 .937 E 10 G 5.4 166 273 2.45 0:35 P WESTERN CAUCASUS 14 - SEP - 90 (257) 20: 40: 18.3 13 .382 N 51 .456 E 10 G 5.4 346 3046 27.39 5:50 P EASTERN GULF OF ADEN 09 - SEP - 90 (252) 02: 14: 51.0 56 .654 N 34 .395 W 10 G 5.4 137 5765 51.84 9:14 P NORTH ATLANTIC OCEAN 15 - AUG - 90 (227) 23: 08: 56.0 43 .757 N 143 .297 E 162 D 5.4 230 7637 68.68 10:51 P "HOKKAIDO, JAPAN REGION" 16 - JUL - 90 (197) 19: 45: 25.1 16 .365 N 120 .546 E 33 N 5.4 266 7652 68.81 11:04 P "LUZON, PHILIPPINE ISLANDS" 03 - MAY - 91 (123) 20: 19: 38.8 42 .683 N 43 .247 E 10 G 5.3 157 309 2.78 0:38 P WESTERN CAUCASUS 06 - JUL - 90 (187) 19: 34: 52.4 36 .861 N 49 .303 E 35 D 5.3 311 540 4.85 1:16 Pn WESTERN IRAN 10 - AUG - 92 (223) 13: 42: 34.9 36 .053 N 69 .706 E 111 D 5.3 274 2225 20.01 4:30 P "HINDU KUSH REGION, AFGHANISTAN" 15 - APR - 91 (105) 10: 48: 59.3 36 .340 N 71 .358 E 124 D 5.3 272 2355 21.18 4:30 P AFGHANISTAN-USSR BORDER REGION 22 - JUL - 90 (203) 11: 20: 09.6 16 .532 N 121 .045 E 33 N 5.3 266 7683 69.09 11:07 P "LUZON, PHILIPPINE ISLANDS" 16 - DEC - 90 (350) 15: 45: 40.7 41 .361 N 43 .715 E 33 N 5.2 148 161 1.45 0:21 P TURKEY-USSR BORDER REGION 03 - MAY - 91 (123) 23: 41: 01.8 42 .647 N 43 .263 E 11 D 5.2 157 305 2.74 0:39 P WESTERN CAUCASUS 18 - JUL - 90 (199) 11: 29: 24.9 36 .990 N 29 .595 E 17 D 5.2 80 1359 12.22 3:07 P TURKEY 07 - DEC - 91 (341) 14: 22: 32.2 25 .191 N 62 .974 E 30 D 5.2 309 2374 21.35 4:51 P SOUTHWESTERN PAKISTAN 20 - AUG - 91 (232) 08: 46: 40.5 37 .646 N 72 .150 E 135 D 5.2 268 2380 21.40 4:43 P TAJIK SSR 14 - AUG - 90 (226) 00: 50: 39.2 27 .024 N 65 .969 E 21 D 5.2 300 2438 21.93 4:56 P PAKISTAN 07 - SEP - 90 (250) 00: 12: 26.2 5 .443 N 31 .686 E 10 G 5.2 22 4072 36.62 7:09 P SUDAN 29 - AUG - 90 (241) 20: 44: 23.0 11 .791 N 95 .034 E 25 D 5.2 288 5830 52.43 9:15 P ANDAMAN ISLANDS REGION 02 - MAY - 91 (122) 01: 25: 30.1 42 .541 N 43 .960 E 10 G 5.1 167 275 2.47 0:32 P WESTERN CAUCASUS 06 - OCT - 91 (279) 01: 46: 47.5 41 .096 N 43 .409 E 18 D 5.0 134 154 1.39 0:24 P GEORGIA-ARMENIA-TURKEY BORD REG 03 - JUN - 91 (154) 10: 22: 40.4 40 .048 N 42 .859 E 28 D 5.0 87 159 1.43 0:13 P TURKEY 04 - JUL - 91 (185) 06: 26: 31.8 42 .387 N 44 .116 E 20 D 5.0 169 256 2.30 0:39 P WESTERN CAUCASUS 27 - MAR - 92 (087) 19: 21: 04.6 42 .456 N 43 .715 E 33 N 5.0 162 272 2.44 0:42 P NORTHWESTERN CAUCASUS 21 - MAY - 91 (141) 17: 37: 38.8 42 .867 N 48 .028 E 10 G 5.0 221 410 3.69 0:49 P CASPIAN SEA 07 - MAY - 92 (128) 19: 15: 02.3 38 .677 N 40 .130 E 10 G 5.0 69 427 3.84 1:15 P TURKEY 28 - DEC - 90 (362) 04: 03: 53.6 37 .106 N 49 .227 E 10 G 5.0 309 516 4.64 1:29 P CASPIAN SEA 08 - SEP - 91 (251) 10: 14: 58.8 36 .264 N 71 .324 E 133 5.0 272 2355 21.17 4:43 P AFGHANISTAN-TAJIKISTAN BORD REG 29 - APR - 91 (119) 11: 51: 10.3 42 .572 N 43 .816 E 10 G 4.9 165 281 2.53 0:34 P WESTERN CAUCASUS 15 - MAY - 91 (135) 14: 28: 50.1 42 .565 N 43 .349 E 14 D 4.9 157 294 2.64 0:36 P WESTERN CAUCASUS 01 - JAN - 91 (001) 19: 18: 56.4 39 .822 N 48 .439 E 61 D 4.9 275 318 2.86 0:48 P N.W. IRAN-USSR BORDER REGION 15 - FEB - 92 (046) 12: 52: 51.7 * 42 .803 N 46 .524 E 15 D 4.9 206 332 2.99 0:52 P EASTERN CAUCASUS 03 - SEP - 90 (246) 02: 40: 59.1 36 .409 N 70 .671 E 202 D 4.9 272 2294 20.63 4:27 P HINDU KUSH REGION 23 - JUL - 90 (204) 20: 54: 56.6 42 .719 N 45 .947 E 33 N 4.8 199 305 2.74 0:47 Pn EASTERN CAUCASUS 27 - JUL - 90 (208) 05: 31: 00.1 37 .318 N 49 .585 E 10 G 4.8 305 525 4.72 1:29 P CASPIAN SEA 21 - AUG - 90 (233) 03: 47: 26.2 37 .309 N 49 .685 E 10 G 4.8 305 533 4.79 1:30 P CASPIAN SEA 28 - JUN - 90 (179) 03: 20: 35.0 37 .085 N 49 .642 E 10 G 4.8 307 545 4.90 1:36 P CASPIAN SEA 01 - JUL - 90 (182) 12: 24: 57.2 37 .181 N 49 .885 E 10 G 4.8 305 555 4.99 1:35 P CASPIAN SEA 20 - AUG - 90 (232) 12: 20: 11.0 * 36 .956 N 49 .720 E 33 N 4.8 308 560 5.03 1:30 P WESTERN IRAN 10 - MAY - 91 (130) 20: 52: 27.3 42 .534 N 43 .986 E 10 G 4.7 167 274 2.46 0:32 P WESTERN CAUCASUS 29 - APR - 91 (119) 11: 10: 11.9 42 .584 N 43 .904 E 10 G 4.7 166 281 2.53 0:35 P WESTERN CAUCASUS 01 - DEC - 91 (335) 09: 17: 27.0 36 .373 N 45 .036 E 35 * 4.7 356 419 3.77 1:08 P IRAN-IRAQ BORDER REGION 01 - JUL - 90 (182) 21: 16: 48.3 37 .285 N 48 .820 E 10 G 4.7 310 476 4.28 1:29 P CASPIAN SEA 27 - DEC - 90 (361) 13: 26: 57.1 36 .539 N 48 .907 E 10 G 4.7 316 541 4.87 1:26 P NORTHWESTERN IRAN 28 - JUN - 90 (179) 03: 42: 01.9 * 37 .079 N 50 .147 E 10 G 4.7 304 581 5.22 1:39 P CASPIAN SEA 19 - JUN - 91 (170) 06: 40: 28.9 40 .282 N 42 .971 E 33 N 4.6 97 150 1.35 0:21 P TURKEY 16 - JUN - 91 (167) 11: 07: 10.6 39 .984 N 42 .875 E 26 D 4.6 85 158 1.42 0:15 P TURKEY 03 - MAY - 91 (123) 06: 08: 37.1 42 .482 N 43 .363 E 10 G 4.6 157 285 2.56 0:37 P WESTERN CAUCASUS 29 - APR - 91 (119) 10: 52: 42.2 42 .712 N 44 .102 E 10 G 4.6 170 291 2.62 0:32 P WESTERN CAUCASUS 10 - MAY - 91 (130) 01: 25: 15.6 42 .496 N 43 .153 E 10 G 4.6 154 294 2.64 0:40 P WESTERN CAUCASUS 24 - SEP - 90 (267) 06: 35: 13.9 * 38 .253 N 47 .951 E 10 G 4.6 306 348 3.13 P NORTHWESTERN IRAN 01 - JUL - 90 (182) 17: 19: 44.1 37 .280 N 48 .818 E 10 G 4.6 310 476 4.28 1:30 P CASPIAN SEA 17 - JUL - 90 (198) 04: 02: 09.2 37 .137 N 49 .979 E 33 N 4.6 304 565 5.08 1:35 P CASPIAN SEA 13 - AUG - 90 (225) 06: 18: 25.1 36 .663 N 49 .884 E 35 * 4.6 309 592 5.33 1:37 P WESTERN IRAN 25 - OCT - 90 (298) 04: 52: 06.0 * 76 .243 N 8 .409 E 10 G 4.6 167 4382 39.41 ?7:47 P SVALBARD REGION 18 - FEB - 92 (049) 01: 39: 40.9 * 41 .477 N 43 .464 E 33 N 4.5 145 183 1.65 0:24 P GEORGIA-ARMENIA-TURKEY BORD REG 30 - JUN - 91 (181) 20: 09: 18.3 42 .424 N 43 .688 E 10 G 4.5 162 269 2.42 0:47 P WESTERN CAUCASUS 02 - MAY - 91 (122) 09: 44: 41.4 42 .507 N 43 .507 E 10 G 4.5 159 283 2.54 0:36 P WESTERN CAUCASUS 29 - APR - 91 (119) 11: 59: 54.8 42 .625 N 43 .962 E 10 G 4.5 167 284 2.56 0:34 P WESTERN CAUCASUS 22 - APR - 92 (113) 03: 03: 47.6 * 39 .557 N 39 .557 E 10 G 4.5 83 446 4.01 1:17 P TURKEY 11 - JUL - 90 (192) 04: 36: 08.6 * 37 .015 N 49 .530 E 33 N 4.5 308 543 4.88 1:35 P CASPIAN SEA 23 - FEB - 92 (054) 12: 03: 11.7 * 36 .391 N 49 .179 E 10 G 4.5 316 569 5.12 1:41 P WESTERN IRAN 10 - OCT - 91 (283) 02: 44: 49.6 41 .399 N 43 .259 E 10 G 4.4 139 187 1.68 0:21 P GEORGIA-ARMENIA-TURKEY BORD REG 05 - MAR - 92 (065) 03: 30: 16.1 38 .263 N 44 .974 E 33 N 4.4 354 209 1.88 0:31 P TURKEY-IRAN BORDER REGION 10 - AUG - 91 (222) 08: 57: 51.8 * 40 .052 N 42 .153 E 10 G 4.4 88 219 1.97 0:46 P TURKEY 17 - JUN - 91 (168) 03: 04: 45.5 * 42 .252 N 44 .222 E 10 G 4.4 170 239 2.15 0:32 P WESTERN CAUCASUS 10 - MAY - 91 (130) 20: 30: 45.3 42 .627 N 43 .449 E 28 D 4.4 159 297 2.67 0:35 P WESTERN CAUCASUS 27 - MAR - 91 (086) 22: 17: 55.0 40 .443 N 45 .443 E 33 N 4.3 240 70 0.63 -0:08 P EASTERN CAUCASUS 12 - NOV - 91 (316) 20: 35: 59.6 * 39 .306 N 44 .936 E 33 N 4.3 349 94 0.84 0:26 P ARMENIA-AZERBAIJAN-IRAN BORD REG 02 - MAY - 91 (122) 02: 07: 31.6 ? 41 .34 N 45 .17 E 10 G 4.3 196 139 1.25 0:45 P EASTERN CAUCASUS 29 - APR - 91 (119) 11: 04: 28.9 * 42 .510 N 43 .816 E 10 G 4.3 164 275 2.47 0:35 P WESTERN CAUCASUS 22 - SEP - 90 (265) 02: 46: 01.2 * 42 .538 N 46 .449 E 33 N 4.3 208 304 2.73 0:34 P EASTERN CAUCASUS 05 - SEP - 91 (248) 19: 23: 04.8 38 .847 N 41 .417 E 10 G 4.3 64 318 2.86 0:48 P TURKEY 22 - AUG - 90 (234) 07: 51: 49.5 * 37 .056 N 49 .327 E 10 G 4.3 309 526 4.73 1:33 P CASPIAN SEA 27 - APR - 91 (117) 03: 31: 58.5 * 40 .093 N 43 .719 E 10 G 4.2 87 86 0.77 0:07 P TURKEY-USSR BORDER REGION 08 - JUN - 91 (159) 01: 12: 01.8 * 41 .005 N 43 .563 E 33 N 4.2 135 138 1.24 0:12 P TURKEY-USSR BORDER REGION 15 - FEB - 92 (046) 15: 18: 04.2 * 41 .434 N 46 .184 E 33 N 4.2 220 190 1.71 0:34 P EASTERN CAUCASUS 03 - MAY - 91 (123) 06: 12: 54.2 ? 41 .93 N 43 .80 E 33 N 4.2 159 214 1.93 0:41 P TURKEY-USSR BORDER REGION 04 - MAY - 91 (124) 04: 53: 35.6 ? 42 .15 N 43 .51 E 10 G 4.2 156 246 2.21 0:41 P WESTERN CAUCASUS 20 - JUL - 90 (201) 17: 30: 36.2 ? 42 .10 N 46 .77 E 33 N 4.2 217 278 2.50 0:50 P EASTERN CAUCASUS 07 - MAY - 91 (127) 09: 01: 23.6 * 42 .606 N 43 .125 E 10 G 4.2 155 306 2.75 0:38 P WESTERN CAUCASUS 15 - FEB - 92 (046) 13: 37: 40.1 42 .934 N 46 .548 E 33 N 4.2 205 346 3.11 0:49 P EASTERN CAUCASUS 02 - AUG - 90 (214) 17: 12: 48.5 * 38 .540 N 48 .186 E 33 N 4.2 300 346 3.12 0:56 P N.W. IRAN-USSR BORDER REGION 23 - DEC - 90 (357) 21: 28: 50.7 * 42 .115 N 44 .356 E 33 N 4.1 172 222 2.00 0:23 P WESTERN CAUCASUS 02 - MAY - 91 (122) 02: 18: 00.1 * 42 .211 N 43 .906 E 10 G 4.1 164 241 2.17 0:32 P WESTERN CAUCASUS 01 - MAY - 91 (121) 23: 19: 11.8 * 42 .719 N 44 .053 E 10 G 4.1 169 293 2.63 0:29 P WESTERN CAUCASUS 02 - MAY - 91 (122) 09: 00: 35.2 * 42 .704 N 43 .692 E 10 G 4.1 164 298 2.68 0:33 P WESTERN CAUCASUS 02 - AUG - 90 (214) 21: 17: 18.7 * 38 .398 N 48 .228 E 33 N 4.1 301 358 3.22 0:55 P N.W. IRAN-USSR BORDER REGION 02 - MAY - 91 (122) 03: 42: 26.1 * 42 .608 N 43 .477 E 10 G 4.0 160 294 2.64 0:42 P WESTERN CAUCASUS 15 - FEB - 92 (046) 13: 30: 32.0 * 42 .462 N 46 .493 E 33 N 4.0 209 298 2.68 0:54 P EASTERN CAUCASUS 02 - MAY - 91 (122) 04: 30: 53.9 * 42 .481 N 43 .201 E 10 G 3.9 155 290 2.61 0:41 P WESTERN CAUCASUS 24 - MAY - 91 (144) 07: 59: 38.8 * 42 .679 N 42 .908 E 10 G 3.9 152 321 2.89 0:26 P WESTERN CAUCASUS 14 - MAY - 91 (134) 09: 36: 25.4 * 42 .609 N 43 .579 E 10 G 3.8 161 291 2.62 0:37 P WESTERN CAUCASUS 26 - APR - 92 (117) 13: 15: 51.2 * 37 .663 N 47 .104 E 33 N 3.8 322 343 3.09 0:56 P NORTHWESTERN IRAN 08 - DEC - 91 (342) 01: 02: 06.2 * 38 .335 N 48 .151 E 33 N 3.8 303 357 3.21 1:02 P ARMENIA-AZERBAIJAN-IRAN BORD REG 04 - JUN - 91 (155) 00: 55: 16.3 40 .600 N 42 .989 E 10 G 3.7 110 156 1.40 0:16 P TURKEY 27 - MAY - 91 (147) 03: 40: 45.5 ? 42 .34 N 45 .86 E 10 G 3.7 201 263 2.37 0:26 P EASTERN CAUCASUS Figure 3-1a. Log-file of G3 tape #28. LOG.G3 3-JUN-92 16:25:19 Rdgeos V10.02: GEOS Tape Log File Default Chan 1 Chan 2 Chan 3 Chan 4 Chan 5 Chan 6 G3 G3A(4) G3A(5) G3A(6) G3B(4) G3B(5) G3B(6) Experiment Location Serial No. Year 28 3 5 1991 File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 1 1 Sensor Cal 121:14:47:27.382 EXT. 0.000 1211447Jn.G3 00:37 1200. 2.06 None Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | *** 506 null values filled in 2 2 Amp Calib 121:14:48:15.683 EXT. 0.000 1211448Fn.G3 00:41 1200. 2.06 None Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | File Clock event Clock time & Standard Old Time & Standard - - - Internal/External Skew - - - 3 VB Synch TMO 121:14:55:35.717 NONE 4 WWVB Corr. 121:14:56:44.000 NONE 0.001 0.000 0.000 0.000 0.001 0.000 0.000 0.000 Mean: 0.000 Std. dev: 1.225 Corr: 0.000 5 VB Synch TMO 121:18:05:35.750 NONE 6 VB Synch TMO 121:21:15:35.816 NONE File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 7 3 Trigger 121:23:19:44.228 EXT. 0.000 1212319On.G3 00:26 1200. 2.06 26.66 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | File Clock event Clock time & Standard Old Time & Standard - - - Internal/External Skew - - - 8 VB Synch TMO 122:00:25:35.889 NONE File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 9 4 Trigger 122:01:26:00.618 EXT. 0.000 1220126An.G3 03:27 1200. 2.06 26.94 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | 10 5 Trigger 122:02:08:17.838 EXT. 0.000 1220208Fn.G3 00:26 1200. 2.06 26.94 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | 11 6 Trigger 122:02:18:31.458 EXT. 0.000 1220218Kn.G3 01:42 1200. 2.06 26.94 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | 12 7 Trigger 122:02:29:34.222 EXT. 0.000 1220229Ln.G3 00:28 1200. 2.06 26.82 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | File Clock event Clock time & Standard Old Time & Standard - - - Internal/External Skew - - - 13 WWVB Corr. 122:02:57:52.004 NONE 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 Mean: 0.004 Std. dev: 0.000 Corr: 0.004 14 VB Synch TMO 122:03:35:35.959 NONE LOG.G3 3-JUN-92 16:25:19 Rdgeos V10.02: GEOS Tape Log File File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 15 8 Trigger 122:03:43:07.589 EXT. 0.004 1220343Cn.G3 00:16 1200. 2.06 26.90 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | 16 9 Trigger 122:04:31:33.992 EXT. 0.004 1220431Ln.G3 01:21 1200. 2.06 26.94 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | 17 10 Trigger 122:06:26:54.759 EXT. 0.004 1220626Sn.G3 00:18 1200. 2.06 26.99 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | File Clock event Clock time & Standard Old Time & Standard - - - Internal/External Skew - - - 18 VB Synch TMO 122:06:45:36.042 NONE File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 19 11 Trigger 122:07:54:04.183 EXT. 0.004 1220754Bn.G3 00:54 1200. 2.06 26.96 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | 20 12 Trigger 122:09:01:07.788 EXT. 0.004 1220901Cn.G3 02:11 1200. 2.06 26.94 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | 21 13 Trigger 122:09:45:18.411 EXT. 0.004 1220945Gn.G3 02:13 1200. 2.06 26.93 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | File Clock event Clock time & Standard Old Time & Standard - - - Internal/External Skew - - - 22 VB Synch TMO 122:09:55:36.110 NONE File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 23 14 Trigger 122:11:58:09.178 EXT. 0.004 1221158Dn.G3 00:35 1200. 2.06 26.94 1 0.4 20. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | *** No. files processed: 23. *** Figure 3-1b. Log-file of G1 tape #03. LOG.G1 18-MAR-91 12:52:21 PCGEOS V04.07: GEOS Tape Log File Default Chan 1 Chan 2 Chan 3 Chan 4 Chan 5 Chan 6 G1 G1A(4) G1A(5) G1A(6) G1B(4) G1B(5) G1B(6) ** Corrupted first GEOS header. Use header file _>..\..\G1.GHD ** ** 2 time cell errors detected ** ** Corrupted first GEOS header. Use header file _>..\..\G1.GHD ** ** 1 time cell errors detected ** ** Corrupted first GEOS header. Use header file _>..\..\G1.GHD ** ** 2 time cell errors detected ** Experiment Location Serial No. Year 0 0 99 1990 File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 3 1 Trigger 183:07:50:43.264 WWVB .000 1830750On.G1 00:16 1200. 2.06 20.00 4 .5 10. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | Experiment Location Serial No. Year 0 1 43 1990 4 2 Trigger 183:08:17:20.104 MAN. .000 1830817Gn.G1 00:16 1200. 2.06 24.38 1 .4 20. 2**3 Ch 1: VEL, 60 dB, 50 Hz | Ch 2: VEL, 60 dB, 50 Hz | Ch 3: VEL, 60 dB, 50 Hz | Ch 4: VEL, 60 dB, 50 Hz | Ch 5: VEL, 60 dB, 50 Hz | Ch 6: VEL, 60 dB, 50 Hz | File Clock event Clock time & Standard Old Time & Standard - - - Internal/External Skew - - - 5 Master Synch 183:08:26:00.000 EXT. 0:00:00:**.007 WWVB .000 .000 .000 .000 .000 .000 .000 .000 Mean: .000 Std. dev: .000 Corr: .000 File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 6 3 Trigger 183:08:28:23.031 EXT. .000 1830828Hn.G1 00:24 1200. 2.06 24.30 1 .4 20. 2**3 Ch 1: VEL, 60 dB, 50 Hz | Ch 2: VEL, 60 dB, 50 Hz | Ch 3: VEL, 60 dB, 50 Hz | Ch 4: VEL, 60 dB, 50 Hz | Ch 5: VEL, 60 dB, 50 Hz | Ch 6: VEL, 60 dB, 50 Hz | Figure 3-1c. Log-file of G1 tape #22. LOG.G1 02-APR-91 16:57:22 PCGEOS V04.07: GEOS Tape Log File Default Chan 1 Chan 2 Chan 3 Chan 4 Chan 5 Chan 6 G1 G1A(4) G1A(5) G1A(6) G1B(4) G1B(5) G1B(6) File Clock event Clock time & Standard Old Time & Standard - - - Internal/External Skew - - - 1 Master Synch 261:08:57:00.000 EXT. ***:**:**:**.000 NONE .090 .090 .090 .090 .090 .090 .090 .090 Mean: .090 Std. dev: .000 Corr: .090 2 WWVB Corr. 261:08:58:39.000 EXT. .000 .000 .000 .000 .000 .000 .000 .000 Mean: .000 Std. dev: .000 Corr: .000 3 WWVB Corr. 261:11:59:47.000 EXT. .000 .000 .000 .000 .000 .000 .000 .000 Mean: .000 Std. dev: .000 Corr: .000 Experiment Location Serial No. Year 0 1 3096 1990 File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 4 1 Continuous 261:12:33:00.878 EXT. .000 2611233An.G1 00:18 1200. 2.06 26.30 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | File Clock event Clock time & Standard Old Time & Standard - - - Internal/External Skew - - - 5 Master Synch 261:14:20:00.000 EXT. 0:00:00:**.003 MAN. .000 .000 .000 .000 .000 .000 .000 .000 Mean: .000 Std. dev: .000 Corr: .000 6 WWVB Corr. 261:14:22:45.000 EXT. .000 .001 .000 .000 .000 .000 .000 .000 Mean: .000 Std. dev: .935 Corr: .000 Figure 3-1d. Log-file of G2 tape #06. LOG.G2 04-APR-91 13:04:07 PCGEOS V04.07: GEOS Tape Log File Default Chan 1 Chan 2 Chan 3 Chan 4 Chan 5 Chan 6 G2 G2A(4) G2A(5) G2A(6) G2B(4) G2B(5) G2B(6) Experiment Location Serial No. Year 6 2 3 1990 .002 .999 .999 .999 .999 .999 .999 .999 Mean: .999 Std. dev: 2.806 Corr: .999 File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 1 1 Trigger 186:13:27:20.632 EXT. -.001 1861327Gn.G2 00:16 1200. 2.06 32.75 4 .7 30. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | 2 2 Trigger 186:13:43:35.032 EXT. -.001 1861343Ln.G2 00:19 1200. 2.06 32.75 4 .7 30. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | File Clock event Clock time & Standard Old Time & Standard - - - Internal/External Skew - - - 3 VB Skew TMO 186:13:54:29.043 NONE 4 WWVB Corr. 186:14:20:23.849 NONE .849 .849 .849 .849 .849 .849 .849 .849 Mean: .849 Std. dev: .000 Corr: .849 File Evt Type Time & Standard Corr DR100 name Duration Srate Pre-event Volts Trg ch STA LTA Ratio 5 3 Trigger 186:15:04:59.974 EXT. -.151 1861504Tn.G2 05:42 1200. 2.06 32.75 4 .7 30. 2**3 Ch 1: VEL, 54 dB, 50 Hz | Ch 2: VEL, 54 dB, 50 Hz | Ch 3: VEL, 54 dB, 50 Hz | Ch 4: VEL, 54 dB, 50 Hz | Ch 5: VEL, 54 dB, 50 Hz | Ch 6: VEL, 54 dB, 50 Hz | Plots of GEOS records for events at five or more sensor locations from 26 June 1990 through 10 August 1992 CHAPTER IV A PC-Based Seismic System for Armenia W. H. K. Lee and E. Cranswick, (U. S. Geological Survey) R. Banfill (Small Systems Support, Big Water, Utah) Introduction Personal-computer-based seismic systems are playing an increasing role in seismic data acquisition and processing. In the past the computer used was usually a mini-computer with specialized hardware and software (costing hundreds of thousands of dollars, and taking several weeks to install). Because personal computers (PCs) are now inexpensive, a PC-based seismic system can be implemented for as little as $5,000 and requires less than one hour to install. A PC-based seismic system expects multiple channels of analog signals (either hard-wired or telemetered) as inputs. The analog signals are usually a few volts in amplitude (peak-to-peak), and will be digitized at a prescribed sampling rate. The system records the digital data either continuously or by event trigger. The PC-Quake System The PC-Quake system (Lee, 1989) is a general-purpose seismic system, with the following characteristics: (1) Uses IBM-compatible 286, 386sx, 386, or 486 PCs with an 8-MHz AT bus. (2) Uses analog-to-digital (A/D) boards (DT 282x series) made by Data Translation, Inc. (3) Digitizes 16 analog channels (upgradable to 128 channels) at user selectable rate. (4) Digitizes up to a few thousand samples per second per channel. (5) Displays digitized data continuously and in real time. (6) Saves digitized data continuously or by event triggering. (7) Automatically picks P-arrivals and locates events. (8) Offline analysis includes manual picking, filtering, FFT, and coda Q. (9) Channel to digitize, or display, or trigger is user selectable. Readers are referred to Lee and Dodge (1992) for more detail. A PC-based Seismic System for Armenia In 1990, a PC-Quake system was implemented in Armenia. This system consists of two identical IBM-compatible 286 PCs with 12-bit, 16-channel A/D boards made by Data Translation. One PC is used for on-line data acquisition and the other PC is used for off-line data processing and analysis. The two PCs are linked by a high-speed local area network (LANtastic kit by Artisoft), and an optical WORM drive (IBM 3363) is used to archive the digitized data on 200-megabyte removable cartridges. The off-line PC also serves as a backup to the on-line unit. A multiplexer could be used to increase the number of channels to a maximum of 256 channels for the 12-bit A/D board (or 64 channels for a 16-bit A/D board). Table 4-1 lists the events recorded on the PC system from 21 September 1990 through 1 January 1991. For those events simultaneously recorded on the GEOS systems the GEOS event name is indicated. Magnitudes as found in the USGS's National Earthquake Information Center's (NEIC's) monthly Preliminary Determination of Epicenters, Arefiev et al. (1991), or as determined in Chapter V of this report are also provided. Note that PC trigger times are based on the relatively inaccurate PC internal clock that drift by several seconds per day. Plots of the PC-XDETECT records follow this chapter. Start-of-record times are indicated on the upper left corner of each plot page (e.g. 09/21/90 07:15 30.359). The plots show the IRIG time signal, ten vertical components (G1AZ to G5BZ), the horizontal components from G1A and G4A (G1AN, G1AE, G4AN, and G4AE), and the sine-wave trigger signal that is activated by a multi-component algorithm. "N" and "E" components are nominally north and east; refer to Table 2-1 for their true orientations. Peak digital counts and relative component scaling factors are indicated at the left of each trace. The time scale shown at the bottom of the page is in seconds. Long events can appear as multiple records across several pages. Table 4-1. Events Recorded by the PC-XDETECT System. PC Trigger Time GEOS Event Magnitude day hr mn sec day hr mn 264 07 15 30.359 1.2 265 02 46 27.049 2650246 4.3 267 06 36 05.487 4.6 278 07 55 09.042 2780757 282 20 53 57.755 0.8 288 07 46 41.022 2880749 0.9 288 18 39 27.696 2881842 1.7 291 11 18 33.428 2911121 2.3 292 13 57 52.289 2921401 300 05 44 32.206 3000549 3.0 312 19 29 39.690 3121935 312 20 37 18.465 1.6 320 06 53 07.991 3200659 1.8 320 07 03 03.516 3200709 1.8 320 14 53 36.909 3201500 2.2 320 14 59 19.400 325 12 24 02.742 3251224 345 08 23 13.789 3450823 349 09 38 49.638 3490939 349 10 38 12.568 3491038 3.3 349 15 40 52.267 3491541 350 15 45 43.419 3501546 5.2 351 01 16 40.201 3510116 351 17 42 49.379 3511742 354 13 02 22.628 3541304 3.5 357 21 27 09.430 3572129 4.1 359 13 18 53.218 3591320 360 10 27 22.928 3601029 363 11 52 03.405 3631154 001 19 17 34.945 0011919 4.9 PC trigger times are much less accurate than the GEOS times. Magnitudes above 4 are MB from NEIC Monthly Listings. Other magnitudes above 3 are from Arefiev et al., 1991. Smaller magnitudes are ML from Chapter V of this report. Plots of PC-XDETECT records from 21 September 1990 through 01 January 1991 Wave-slowness contour plots for selected events CHAPTER V Near-Surface Measurements of P- and S-Wave Velocities from the Dense Three-Dimensional Array near Garni, Armenia J. Mori, J. Filson, E. Cranswick, R. D. Borcherdt, G. Glassmoyer, and W. H. K. Lee, (U. S. Geological Survey) R. Amirbekian, V. Aharonian (Yerevan Seismic Station) L. Hachverdian (Armenian Academy of Sciences) Abstract P- and S-wave arrivals from local earthquakes were studied using an array of ten three-component instruments in and around a tunnel at Garni Observatory, Armenia. The array has a three-dimensional configuration with lateral dimensions of 300 to 500 m and a depth extent of 100 m. Estimates of the horizontal and vertical components of slowness for P and S wavefronts were used to determine the angles of approach and the propagation velocity. The results show that the region around the array has low average velocities for both P (1.43 km/sec) and S (0.61 km/sec) waves, so wavefronts approach the array at steep angles of incidence. Waveforms from one event show clear reflections from the free surface for both P and S waves. The timing of these reflections gives the velocity variation with depth within the array. We estimate a P-wave velocity of 0.33 km/sec within a few meters of the surface increasing to 6.0 km/sec for the deepest portion of the array. Local site variations can greatly complicate the high-frequency waveforms even for tunnel stations in bedrock. The S waves exhibit stronger site-dependent waveforms and time delays than do the P waves. Introduction An array of ten three-component instruments was installed in and around a 200 meter horizontal tunnel (Figure 5-1) at Garni Observatory, Armenia (40.136oN, 44.724oE). The Garni array is located on the lower southwestern slope of Mt. Azhdahak in the Gegham Range of central Armenia. Mt. Azhdahak is a Cenozoic volcanic center with layered tuffs dominating the geology near the tunnel. With horizontal spacings of 60 to 480 meters and vertical spacings of 14 to 100 meters, this dense array provides one of the few opportunities to record three-components of ground motion in a three-dimensional array. We have used these data to make measurements of the three-dimensional slowness for incoming P and S arrivals from eleven earthquakes at distances of 10 to 60 km. These three-dimensional slowness estimates are useful because they show the angle of incidence with which the wavefront approaches the array and also directly give the velocity of the material in the region of the array. The predominant frequencies of the data used in this study are from 3 to 20 Hz which correspond to wavelengths of 90 to 570 meters for the P wave and 30 to 170 meters for the S wave. The instrument spacing is comparable to these wavelengths, so we are able to accurately map wavefronts as they pass through the upper 100 meters of the near-surface material. The first part of this paper treats the data as single incoming wavefronts and we estimate the directions of approach and the average propagation velocity across the array. The second part of the paper looks at one specific detail of the waveforms, the free-surface reflections. The relative arrival time of the reflection as a function of station depth gives more information about the depth dependent velocity variation within the array. Data The data for this study were recorded by 1 Hz (Mark Products L4C) velocity transducers both on a triggered IBM-compatible personal computer (PC) system at 200 samples/second/channel with 12-bit resolution (Tottingham and Lee, 1989) and on the General Earthquake Observations System (GEOS) recorders (Borcherdt et al., 1985) at 200 samples/second/channel with 16-bit resolution. The PC system recorded all ten vertical and four horizontal components with a common time base. The five GEOS instruments recorded the complete three-component data for all ten sites. Comparisons between the two systems show spectral coherence above 0.9 in the frequency range of 1 to 50 Hz. The P-wave data used in this study were primarily taken from the PC system. The S-wave data were taken from horizontal components recorded by the GEOS system. We studied eleven earthquakes recorded by the array from September through November 1990 (Table 5-1). Approximate hypocentral distances (km) were determined by multiplying the S-P time (seconds) by 7.8. Magnitudes were determined by convolving a Wood-Anderson instrument response with the data to produce equivalent Wood-Anderson amplitudes (Kanamori and Jennings, 1978). Amplitudes from all the available horizontal components (four to twenty per event) were used with the Richter (1937) distance correction to obtain the magnitudes. Based on the similarity of the waveforms and the relative arrival times, three of the earthquakes were located closely together at a hypocentral distance of about 12 km, nearly under the array (events 4, 5, and 8 in Table 5-1). Another two events (9,10), located 20 km to the east, also have similar hypocenters. The remaining 6 earthquakes arrived from a wide spread of azimuths (Table 5-1). Figure 5-2 shows an example of the data for event 11. The P waves show similar impulsive waveforms across the array that are well suited for timing arrivals. The S waves on the horizontal components are also fairly clear, although some procedure of waveform matching is needed to accurately estimate arrival times. There are significant differences both in waveform and amplitude among these sites, which are located within a few hundred meters of each other. Differences in site response for closely spaced stations have also been noted at other arrays, such as in New York state (Menke et al., 1990) and southern California (Vernon et al., 1991; Mori, 1993). These site-response characteristics, especially for the S wave, are an indication of the problems that will be encountered in studying coherent wavefronts across the array. Three-Dimensional Slowness Measurements For a plane wave traveling across a three-dimensional array of stations, the arrival time (ti ) at station i can be written as, ti = Sx xi + Sy yi + Sz zi , where Sx , Sy , Sz are the three components of slowness and xi , yi , zi are the spatial coordinates of the i th station. With arrival times measured at four or more sites distributed in space, the slowness in three dimensions can be determined. For the data used in this study, we determine the slowness vector using a grid search method that tests the correlation of the waveform data for each value of the three-component slowness. This is a three-dimensional extension of the two-dimensional method used by Frankel et al. (1991) to study apparent velocities with a small aperture array. The procedure used in this study consists of: 1. Calculating the relative arrival times at each station for the given value of slowness. 2. Shifting the waveforms by these time lags. 3. Calculating the cross correlation of each pair of stations and summing the values. For 10 arrivals, this involved 45 cross correlations. The combined cross correlation for all the station pairs is a measure of how well the relative arrival times fit the given value of slowness. In this manner we searched for the three components of slowness that that give the highest correlation of the waveforms. After determining the slowness vector, the back azimuth (f) to the event is, f = arctan(Sx/Sy) . The incoming angle of incidence (q) from vertical is, q = arctan((Sx2 + Sy2)1/2 / Sz) . The apparent velocity (Va) is, Va = 1/(Sx2 + Sy2)1/2 . The material velocity (Vo) is, Vo = 1/(Sx2 + Sy2 + Sz2)1/2 . We used time windows of 0.5 sec for the P wave and 0.7 sec for the S wave to compute cross correlations. The slowness was tested in increments of 0.03 sec/km. An example of the grid search for the P-wave window of the event recorded at 1500 on 11/16/90 is shown in Figure 5-3. The contoured values of the combined correlation are shown for horizontal and vertical slices out of the three-dimensional slowness space that was searched. The contour interval is 0.05. The highest values of the correlation for the P wave (shaded areas) show an incoming wavefront with a horizontal slowness of 0.12 sec/km (corresponding to an apparent velocity of 8.3 km/sec) moving toward the southwest in the horizontal slice. In the vertical slice the P wave is approaching the surface at an incidence angle of 11 degrees with a total slowness of 0.64 sec/km (P-wave velocity of 1.56 km/sec). The S-wave window (Figure 5-4) shows a wavefront of similar orientation moving with a horizontal slowness of 0.30 sec/km (apparent velocity of 3.3 km/sec) in the horizontal slice and total slowness of 1.71 sec/km (S-wave velocity of 0.58 km/sec) in the vertical slice. In the horizontal slices, the contours are elongated in the east-west direction, indicating that there is better resolution for the north-south slowness than for the east-west slowness. This is due to the geometry of the array. The stations tend to be lined up in the direction along the axis of the tunnel, so that there is good station spacing in the north-south direction and more limited distribution of stations in the east-west direction. The contours in the vertical slice show contours that are elongated in the vertical direction, which is also probably due to station geometry. Since the vertical extent of the array is only 100 meters compared to the larger horizontal extent of 300-500 meters, there is a better constraint on the horizontal slowness compared to the vertical slowness. Another reason for poorer resolution in the vertical direction could be due to strong velocity variations as a function of depth. In addition to the grid search method described above, we checked our results by picking the onset times and directly determined the slowness using a least-squares fit to the arrival times. In general the two methods give consistent results. The advantage of the more tedious grid search method is that the cross correlations look at a larger portion of the waveform and are particularly useful for emergent P and S waves, where it is difficult to accurately pick the onset of the arrival. Also, searching through the whole slowness space shows the range of values that is consistent with the data and is useful for identifying directions from which secondary energy is arriving across the array. Slowness Results Using the grid search method, we determined the P-wave slowness for the eleven earthquakes and also the S-wave slowness for six earthquakes. There were incomplete horizontal data to determine S-wave slowness for the other five events. The cross correlation values generally have well-defined maxima, giving good estimates of the horizontal and vertical slowness. For the P waves, the results presented in Table 5-1 show a large spread of incoming azimuths with steep incidence angles. 6 of the events (1, 4, 5, 7, 8, and 11) have large apparent velocities (>10 km/sec), indicating relatively deep earthquakes with raypaths to the array that take-off upward from the source. The other events, even to a distance of greater than 60 km, also have steep incidence angles (< 20 degrees) which is an indication of low-velocity material in the near-surface region. The low-velocity material will bend the ray paths toward the vertical as they approach the surface. One consistent result for all events is the P-wave velocity for the region near the array. For the wide range of incoming azimuths the estimates for the P-wave velocity had a standard deviation of 15%. The average velocity was determined to be 1.43 + 0.22 km/sec. The stated uncertainty is one standard deviation. For the S waves, the north and east horizontal components were rotated into a transverse direction assuming the back-azimuth obtained from the P wave, before the cross correlation procedure was run on the waveforms. The estimates of the incoming S wavefronts are generally in agreement with the P wavefonts. However, there is more variation among the S waveforms compared to the P, thus the correlation values were lower indicating more uncertainty in the results. The determinations for the back azimuth to the event and the vertical incidence angle are within 14 degrees of the values from the P waves. This indicates that the P and S wavefronts are approaching from approximately the same angle. The average S-wave velocity is 0.61 + 0.06 km/sec. This gives a high P to S velocity ratio of 2.3 + 0.2. As mentioned above there tends to be more uncertainty in the S-wave estimates because of the variation in waveforms across the array. At a given frequency, the S waves might be expected to show more variations than the P waves, because the S-wave velocity is slower than the P-wave velocity and the wavelength is correspondingly shorter. For this reason, the S waves might also be more sensitive to site-dependent time delays. Figure 5-5 shows the P- and S-wave arrivals for the event at 1839 on 10/15/90. Note that the pattern of relative arrival times across the array is quite similar for the P and S, with the exception of G5A, where the S wave arrives late. This significant S-wave site delay appears to be azimuthally dependent and is strong for events 5 and 8, which approach the array steeply from the northwest. For these two events, G5A was not used in the S-wave slowness analyses. There is also some evidence that the delay could be due to phase response problems in the instrumentation at G5A. Free-Surface Reflections Figure 5-6 shows the P- and S- wave arrival from the event at 1839 on 10/15/90 as recorded on the tunnel stations and one surface station directly above, plotted as a function of station depth. The instrument response was removed to convert the data to ground displacement and the waveforms were aligned on the first arrival. Note that there is a secondary arrival (dashed line) following both the initial P and S arrivals on the tunnel stations, but not on the surface station. This arrival is interpreted to be the downward reflection from the free surface, since it moves out with station depth. The timing and polarity of this arrival is also consistent with the direct arrivals at the surface station G4A and the tunnel station G1A located 60 meters directly below. Between these two stations there is a 0.04 sec time difference in the direct P arrival which corresponds to the 0.08 sec two-way travel time of the surface reflection seen on G1A (Figure 5-6). This type of arrival has been previously observed from borehole data (Hauksson et al., 1987). The amplitude of the first arrival at the tunnel stations is about half that of the surface station. This difference can be partly explained because the energy is divided between the direct and reflected arrivals for the sub-surface stations, while for the stations on the surface all the energy is contained in the direct arrival. Also, there is an amplitude difference because the surface station is sited on lower-velocity material. At these high frequencies, the tunnel sites show more complicated waveforms than the surface sites. These differences in waveforms may affect the estimated slowness, if the waveform correlations are dominated by these high-frequency characteristics. To avoid this, we use relatively long (0.5 to 0.7 sec) time windows to give more weight to the lower-frequency components. We can use this secondary arrival to estimate the P-wave velocity in the material between the tunnel stations and the surface. Assuming that the ray is traveling at a near-vertical angle of incidence as indicated by the slowness results, the time difference between the direct and reflected arrivals is the two-way travel time from the station to the surface. The measured times give average velocities of 0.33, 0.70, 1.1, and 1.5 km/sec for the material between the surface and stations G3A, G2A, G2B, and G1A, respectively, as shown in the top portion of Figure 5-7. If we assume that the velocity structure is parallel to the topography, the data can also be interpreted as a layered structure shown in the bottom portion of Figure 5-7, with velocities ranging from 0.33 km/sec at the surface to 6.0 km/sec at a depth of 60 m. The layer thicknesses in this model were arbitrarily set to match the station spacings. The actual velocity structure may be quite different from either of the simple models shown in Figure 5-7, especially given the various layers of volcanic tuff that are observed in the local geology near the tunnel. However, at present we do not have data to constrain the velocity of these more complicated structures. The S waveforms in Figure 5-6 are very similar to the P waveforms, therefore the timing of the reflection phases gives an S-wave velocity structure similar to the the P-wave velocity structure but with 0.5 times the velocity. This P to S velocity ratio of 2.0 is the same as obtained from the slowness analysis for this event. The ratio of 2.0 measured from the reflected arrivals is probably the more reliable estimate because it is a direct measurement of the time differences of P and S waves arriving along similar paths. Discussion We do not have independent determinations for the locations of these events, so it is difficult to judge the accuracy in the estimates for back azimuth and incidence angles. The estimates of the P- and S-wave velocities are much better constrained. The largest time differences are between the tunnel and surface stations, indicating that most of the arrivals have steep angles of incidence. Therefore, small errors in the back azimuth and incidence angle do not affect the velocity estimates significantly. This is reflected in our consistent estimates of the material velocity. Determination of apparent velocity for steep incidence angles are strongly dependent on the angle of incidence, so there is much more uncertainty in these values. The slowness analysis used in this study assumes a plane wave incident on the array. This assumption breaks down for any vertical or lateral variations in velocity near the array, as was clearly inferred from analysis of the reflected phases. However, the values from the slowness analyses are still meaningful as velocities for the near-surface region averaged over the dimensions of the array. In particular, since the largest time differences are measured between the tunnel and surface stations, the velocity estimates in our study are dominated by the near-surface material above the tunnel. The consistent results we obtain for a wide range of P-wave azimuths indicate that lateral variations are not strong enough to affect the P-wave velocity estimates. However, there appear to be stronger lateral variations in the S-wave velocity structure to the extent that incoming wavefronts are not as well approximated by a plane wave. The velocities estimated by the slowness method are also frequency dependent, since lower frequencies, corresponding to longer wavelengths, will sample material properties deeper in the crust. We see this effect in the higher P-wave velocity for event 2, which was the most distant event (S-P time > 9 seconds) and had P waves with the lowest frequencies. This is further evidence that the low velocities are associated with the near-surface material. In additon, the most direct evidence for the very low velocities near the surface are the time delays from the free-surface reflections at tunnel stations. Using four tunnel stations at various depths below the surface, we see a strong increase of both the P- and S-wave velocities with depth (Figure 5-7). The range of values we obtain are similar to the results from a borehole experiment at Anza, California (Fletcher et al., 1990) and show P-wave velocities near the surface of a few hundred meters per second and increasing to several kilometers per second at 50 to 100 meters depth. This strong depth dependence of the velocity is some of the detailed velocity structure that is blurred together in our average P-wave velocity of 1.43 km/sec obtained from the slowness method. This three-dimensional array experiment has been useful for making direct estimates of the P- and S-wave velocities and providing approximate locations of local earthquakes (Figure 5-8). Knowledge of the near-surface velocities is important for evaluating the site effects associated with strong ground-motions. However, in the slowness analysis we assume that the region around the tunnel was a uniform medium, and thus obtain only average near-surface velocities. Denser instrumentation would be useful for studying the lateral variations that exist on the scale of tens to hundreds of meters. These site conditions affect the ampltudes of the high-frequency waves and also affect our direction estimates of the incoming wavefronts. Further, for the purposes of more accurately locating earthquakes, the aperture of the array should be expanded to several kilometers. Even in that case, it would be necessary to have some indepently known source locations to detemine the individual site delays. Conclusions Estimates of slowness for incoming P and S waves recorded on the Garni three-dimensional array show steep incidence angles from local earthquakes. These arrivals give average P- and S-wave velocities of 1.43 + 0.22 and 0.61 + 0.06 km/sec, respectively, for the region around the array. Since the data used for slowness correlations have relatively high predominant frequencies (3-20 Hz), these values reflect the material close to the ground surface. This result was confirmed by measurements of the time delays from free-surface reflections observed on the tunnel stations. The P-wave velocity profile inferred from the surface reflections varied from 0.33 km/sec near the surface to 6.0 km/sec at 60 meters depth. At the higher frequencies used in this study, the tunnel sites have more complicated waveforms than the surface sites, because of the reflection off the ground surface. In addition to differences in waveform and amplitude between the closely spaced instruments, there are also arrival-time delays which are particularly strong for the S wave and affect the ability of the array to resolve the incoming azimuth of seismic waves. Despite the high frequency complexities observed in the incoming wavefronts, the array was still useful for giving approximate locations of small earthquakes in the immediate region, which may be important for seismic hazard assessments. Garni lies on the northern edge of a narrow, east-west trending valley, a strong topographic feature that may be due to active faulting. This feature extends west to the outskirts of Yerevan, a city of 1.2 million people. Acknowledgements E. Sembera, C. Dietel, K. Safarian, H. Galagian, G. Apoian, and K. Kirakossian supplied technical support for the instrumentation. R. Banfill wrote much of the software for the PC system. The research is part of the Joint Seismic Program led by the Incorporated Research Institutions for Seismology (IRIS). This research was sponsored by the Defense Advanced Research Projects Agency and the Air Force Office of Scientific Research through the Air Force Geophysical Laboratory and the National Science Foundation. The work was carried out under the aegis of Area IX of the U.S./U.S.S.R Agreement on Cooperation in the field of Environmental Protection. D. Eberhart-Phillips and S. Hough provided helpful comments on this paper. Table 5-1. Parameters of incident plane waves from events recorded on the Garni array. Distances were estimated from S-P times. Magnitudes were determined by convolving a Wood-Anderson instrument response with the data. P wave S wave Back Apparent Incidence Back Apparent Incidence No. Date Time Distance Magnitude Azimuth Velocity Velocity Angle Azimuth Velocity Velocity Angle (km) (deg) (km/s) (km/s) (deg) (deg) (km/s) (km/s) (deg) 1. 09/21/90 0715 16 1.2 282 16.7 1.28 4 2. 10/05/90 0755 >60 294 8.3 2.02 14 3. 10/09/90 2054 12 0.8 176 4.2 1.27 18 4. 10/15/90 0746 12 0.9 338 11.1 1.44 7 5. 10/15/90 1839 12 1.7 338 11.1 1.44 7 326 6.7 0.71 6 6. 10/18/90 1118 30 2.3 82 6.7 1.21 11 90 3.3 0.55 10 7. 10/27/90 0544 42 3.0 204 11.1 1.44 7 198 10.0 0.62 4 8. 11/08/90 2037 12 1.6 354 16.7 1.33 5 8 5.0 0.62 4 9. 11/16/90 0653 20 1.8 74 6.7 1.36 12 80 3.3 0.58 10 10. 11/16/90 0703 20 1.8 74 6.7 1.36 12 11. 11/16/90 1500 14 2.2 32 8.3 1.56 11 34 3.3 0.58 10 Figure 5-1. Approximate station configuration for the three-dimensional Garni Array. G5B which appears to be above the ground is on a hillside slope east of the array. Figure 5-2. Example of the three-component velocity data for the event at 1500 on 11/16/90. Figure 5-3. Contoured plots of combined cross correlation values for tested values of slowness from the P-wave window of the event at 1500 on 11/16/90. Vertical (top) and horizontal (bottom) slices of the three-dimensional slowness space are shown. High correlation values (shaded areas) correspond to values of slowness which are consistent with a plane-wave propagating across the array. Figure 5-4. Contoured plots of combined correlation values from the S-wave window of the event at 1500 on 11/16/90. Figure 5-5. P- and S-wave arrivals for the event at 0746 on 10/15/90. Note that the relative arrivals for the P and S are similar, except at G5A where the S wave arrives significantly late. Figure 5-6. Ground displacements of the P and S waves for the event at 1839 on 10/15/90. Reflections from the free surface (dashed line) can be seen following both the P- and S-wave arrivals at the tunnel stations. Figure 5-7. (Top) Average P-wave velocities between the tunnel stations and the ground surface from time delays of surface reflections. (Bottom) Velocity model consistent with the time delays of the surface relections, assuming a layered structure parallel to the topography. Figure 5-8. Rough locations of the numbered events from Table 5-1 shown on a map of northern Armenia. REFERENCES Arefiev, S., I. Parini, K. Pletnev, A. Romanov, D. Mayer-Rosa, and P. Smit (1991). "Spitak (Armenia, USSR) 1988 Earthquake Region: Strong-Motion Data of Selected Earthquakes June 1990 - April 1991", Technical Report No. 104, Publication Series of the Swiss Seismological Service, Federal Institute of Technology, Zurich, Switzerland. Borcherdt, R. D., J. B. Fletcher, E. G. Jensen, G. L. Maxwell, J. R. VanSchaak, R. E. Warrick, E. Cranswick, M. J. S. Johnston, and R. McClearn (1985). A general earthquake observation system (GEOS), Bull. Seismol. Soc. Am., 75, 1783-1826. Borcherdt, R. D. 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