This directory contains recordings of the Parkfield 2004 main shock obtained in the SAFOD Pilot Hole.  

Exact location of Pilot Hole

Latitude:       
35 deg  58 min  27.3286 sec
35.97425794  deg

Longitude:      
-120 deg  33 min  07.5857 sec
-120.55210714  deg

Elevation  667.5 meter   (2190 ft)


The data were recorded at 500 samples/sec on the Geores recording system at SAFOD.  The sensors are 15 Hz 3-component geophones. 

SAFOD_3com_instruments.txt gives the original channel assignments, level names (Pods) and depths below the ground surface in feet.  Because of the intersection of the main hole into the pilot hole, only pods 26 through 32 are operational.  They appear in positions 10 through 30 in the multiplexed data files.  The order of components is z, h1, h2 at each level.  (S26 z is in column 10, S26 h1 is in column 11, ... , S32 h2 is in column 30).

Pilot_Hole_Sonde_Positions.txt contains coorninate and orientation information for each level.  This information was developed by Volker Oye as part of his theis work at NORSAR.  A manuscript "Orientation of three-component geophones in the San Andreas Fault Observatory at Depth Pilot Hole, Parkfield, California" by Volker Oye and William L. Ellsworth has been submitted to BSSA.

There are 8 data files each with 65.532 seconds of data (32768 data points).  The earliest file, 0987, is immediately before the main shock.  File 0988 contains the main shock.  Note that there is a small gap between consecutive files of 30-35 msec.  Data in the gap were not recorded and are lost.

Recordings on the vertical component remain onscale through the earthquake.  The horizontal componets clip for a few cycles.  From the appearance of the data the clipped peaks are about a factor of 2 above the clipping level.

The data are given in two formats.  ASCII flat files (30 columns by 32768 rows) appear in the *.txt files.  SEG-2 files are in the *.dat files.

The data in the files are the milivolts output of the instruments

Instruments detailes:
Sensors:                          GeoSpace GS-20DM 
Natural Frequency:                15 Hz 
DC resistance:                       2400 Ohms 
Intristic Voltage Sensitivity:    2.64 V/in./sec, 1.040 V/cm/sec (Whole system; see comment below *) 
damping:                               0.57 
Moving Mass                        7.8 gr 

*Two sensors are connected in series so the Voltage Sensitivity is twice the single instrument output of 1.32 V/in./sec



Peter Malin             Duke University
Eylon Shalev
Andres Chavarria

Bill Ellsworth  USGS Menlo Park