XMM1
Middle Mountain Creepmeter

Electronics for this instrument were changed on
March 7, 1996. Scale factor to coverting DCP counts
to RL slip in mm was changed from 142 to 133. Cleaned
data below has this change included; However, there
may be a slight offset in the data which has not
necessarily been taken-out.


The Sept 28, 2004 Parkfield Earthquake caused the wire to
stretch beyond the limits of the micrometer. (ie, the meter 'pegged')
Released tension on wire by feeding 68mm from the anchor end; Micrometer
read -0.7mm

It appears the both the 'Big Creep' counter gauge and electronics
worked through the EQ.


Examination of the differences between the micrometer and telemetry
values indicate that the calibration of this meter is not correct.
In particular, the data from 1993 to 1996 (and perhaps the period 
between 1986 and 1988) indicate a mis-calibration. The equipment change
in 1996 is documented above. Finally, the post-Parkfield EQ data
indicate another change in calibration; but there was no equipment
change. We will investigate this, soon.

Sept-October 2005; The wire had lots of friction due to that 6 inch diameter
conduit pulling apart from slip on the fault; the
pull-apart allowed for the soil to cave-in and covered the wire. 
The wire was replaced and the conduit was patched.

May 2007; swap-out electronics and DCP for a new version; Telemetry 
voltage range now 0-5v; scale factor is now 147 counts(mv) per mm 
fault slip (creep).

Note ---  (Aug 2022)  The data from ~June 2021 and the present suggest
that site is not detecting creep --- rate has been 0mm/yr -- expect something
like 10 mm/yr rate
 
          General Notes:
    FAULT CREEP DATA FROM PARKFIELD

The following data represent real-time measurments of fault slip across
the San Andreas fault or its "south-west" trace near Parkfield, CA.
Creepmeters consists of 2 piers separated by about 30 meters and
connected by an invar wire.  The main fault-trace lies between the 2
piers.  The wire is at roughly a 30 degree angle from the local trace
of the fault. A displacement tranducer measures the change in length of
the wire (or the change in distance between the piers). These
measurements are made once every 10 minutes and are telemetred to Menlo
Park. In addition, micrometer measurements are periodically made by
"hand". The telemetred creep data are reconciled with the micrometer
measurements. The data have been reconciled with the
micrometer measurements and then decimated to daily measurements and
scaled to represent fault slip in mm. 

The data provided here has been processed such that telemetry
glitches have been removed, data edited for electronic and other
problems, offsets due to resets of the instrument have been removed,
and the telemetried data have been reconciled with the Micrometer
measurements.

Please note that when computing secular rates and other statistics that
the assumption of data independence (ie gaussian distributed data) is
NOT correct. For starters, the statistics of the data are a mixture of
random-walk and white (gaussian) noise.  You'll need to construct the
appropriate data covariance matrix to account for these noise sources.
Otherwise, if you let your standard least squares routine compute the
secular rate and its standard error, that error bar will most likely be
too small relative to the true estimate of standard error.

Because the pier are installed at shallow depths (2-3 meters), these
piers will tilt in responce to rainfall. ONE NEEDS TO EXAMINE RAINFALL
RECORDS WHEN INTERPRETING THESE CREEP MEASUREMENTS. 

Many people have contributed to this project including:
Robert Burford
Sandy Schultz
Kate Breckinridge
Rich Liechti

For questions, contact John Langbein (langbein@usgs.gov)
  or Andy Snyder (asnyder@usgs.gov)