TOMOG3D (Cerro Prieto) PASSCAL Experiment 9704 Hubert Fabriol Jose Frez Cardenas CICESE - Earth Science Division Dept. of Seismology Ensenada, Mexico Overview -------- Cerro Prieto was microseismic monitoring project located near the Cerro Prieto geothermal field in the Salton trough, northern Baja California, Mexico. Objectives of the study included studying the seismicity of the Cerro Prieto and Imperial faults, as well as acquiring data for a joint inversion for hypocenter and 1-D or 3-D velocity structure. Acquisition ----------- Sixteen short-period stations recorded triggered events at 200 samples per second from March 17 through May 17, 1997. Triggering was based on a short-term amplitude average (STA) over 0.5-1 seconds versus a long-term average (LTA) over 30-50 seconds; the trigger ratio (STA/LTA) varied from 2 to 4. Record length was 45 seconds. The number of events with four or more associated station triggers totaled 485. The network included three-channel REF TEK A07 recorders with 24-bit A/D convertors and primarily Mark Products L22 sensors having a 2 Hz corner frequency (plus one Guralp CMG-40T sensor with a 0.0333 Hz corner frequency). The stations and their instrumentation, channel orientations, and locations are summarized in the following table. Site DAS# Sensor# Model Chan/dip/azi Time span Latitude Longitude Elev ----- ---- ------- ------ ------------------- ------------ -------- ---------- ----- ES03 7359 473 L22 1/90/0:2/0/0:3:0/90 1997:079-136 32.32209 -115.26847 -31.0 ES04 7432 477 L22 1/90/0:2/0/0:3:0/90 1997:076-136 32.34537 -115.19821 -31.0 ES07 7335 1501 L22 1/90/0:2/0/0:3:0/90 1997:077-136 32.37339 -115.32405 -25.0 ES08 7356 781 L22 1/90/0:2/0/0:3:0/90 1997:076-079 32.37443 -115.22913 -26.0 464 L22 1/90/0:2/0/0:3:0/90 1997:080-093 480 L22 1/90/0:2/0/0:3:0/90 1997:093-137 ES11 7349 468 L22 1/90/0:2/0/0:3:0/90 1997:093-114 32.39888 -115.29561 -26.0 ES16 7320 512 L22 1/90/0:2/0/0:3:0/90 1997:077-137 32.42936 -115.29464 -31.0 ES18 7449 1496 L22 1/90/0:2/0/0:3:0/90 1997:076-077 32.42574 -115.23012 -28.0 7348 1496 L22 1/90/0:2/0/0:3:0/90 1997:080-137 ES21 7361 1494 L22 1/90/0:2/0/0:3:0/90 1997:079-136 32.43647 -115.33643 -30.0 ES23 7443 465 L22 1/90/0:2/0/0:3:0/90 1997:077-136 32.45906 -115.22820 -31.0 ES25 7442 490 L22 1/90/0:2/0/0:3:0/90 1997:077-119 32.45340 -115.16113 -19.0 781 L22 1/90/0:2/0/0:3:0/90 1997:120-136 M201 7349 468 L22 1/90/0:2/0/0:3:0/90 1997:114-137 32.40981 -115.17375 -21.0 M206 7347 4300 CMG40T 1/90/0:2/0/0:3:0/90 1997:079-132 32.43399 -115.13580 -19.0 NVL 7349 480 L22 1/90/0:2/0/0:3:0/90 1997:087-092 32.39873 -115.21191 -21.0 QKP 7447 1493 L22 1/90/0:2/0/0:3:0/90 1997:078-136 32.30538 -115.33291 7.0 TLX 7454 501 L22 1/90/0:2/0/0:3:0/90 1997:077-136 32.47310 -115.14587 -18.0 VEX 7344 472 L22 1/90/0:2/0/0:3:0/90 1997:077-136 32.36295 -115.10533 -25.0 Channel orientations are described according to SEED convention where dip is measured in degrees down from horizontal; azimuth is expressed as degrees from geographic north. Response files describing the sensor and digital acquisition system filters are included in the response_file directory on tape. The following station response cascades refer to these file names. Station M206 has the following response cascade: Stage Filename Description ----- --------------------------- ---------------------- 1 response_files/cmg40t_vel sensor 2 response_files/RT72A07_200 A/D; input 102,400 sps 3 response_files/crystal.1 decimate by 8 4 response_files/crystal.2 decimate by 2 5 response_files/crystal.2 decimate by 2 6 response_files/crystal.2 decimate by 2 7 response_files/crystal.2 decimate by 2 8 response_files/crystal.2 decimate by 2 9 response_files/crystal.3 decimate by 2 All other stations have the response cascade: Stage Filename Description ----- --------------------------- ---------------------- 1 response_files/l22_vel sensor 2 response_files/RT72A07_200 A/D; input 102,400 sps 3 response_files/crystal.1 decimate by 8 4 response_files/crystal.2 decimate by 2 5 response_files/crystal.2 decimate by 2 6 response_files/crystal.2 decimate by 2 7 response_files/crystal.2 decimate by 2 8 response_files/crystal.2 decimate by 2 9 response_files/crystal.3 decimate by 2 Station Timing -------------- All traces have been corrected to GPS time with the exception of station QKP from April 4 through May 13, 1997 (Julian days 094-133). The QKP clock did not lock with the GPS constellation during this time. Data Organization ----------------- The Cerro Prieto assembled data set was prepared at the PASSCAL Instrument Center by Mary Templeton and submitted on a tape containing seven individual UNIX tar files: File # Directory Description ------ --------- ----------- 1 Report.txt This document. (8 KB untarred) 2 events associated PASSCAL SEGY traces in event-network directories; names are as follows: 97.136/97.136.04.46.02/01/ES21..97.136.04.46.03.7361.1 where 97.136 is the year and Julian day, 97.136.04.46.02 is the event trigger time, 01 is the data stream number, and ES21..97.136.04.46.03.7361.1 is the SEGY trace for station ES21, REF TEK serial number 7361, channel 1. The events subdirectory also contains an associated.log file that lists the pathnames of traces belonging to each event. This file is useful for viewing the events with viewer such as the PASSCAL pql program. (312.91 MB untarred) 3 log_files files containing state of health, timing, and acquisition information. Files are named as follows: ES16.1997.119_137.7320.log where ES16 is the station, 7320 is the REF TEK serial number, and 1997.119_137 is the year and Julian day time span described by this file. These files were written by the ref2segy program. (17.00 MB untarred) 4 response_files sensor poles and zeros and REF TEK A/D and fir filters described in the Acquisition section. (10 KB untarred) 5 time_correction_files PASSCAL Clock Files (PCF) containing time corrections applied to the SEGY traces. These files were written by the refrate program and are named as follows: ES08.1997.119_137.7356.log.pcf where ES08.1997.119_137.7356.log is the log file used as input to the refrate program. (2.63 MB untarred) 6 timing_err_files timing error files created by ref2segy named in the same manner as the log files. These files reflect timing gaps and overlaps for continuous data, but for triggered data, they indicate mainly the segmented nature of recording. (485.22 MB untarred) 7 unassoc_traces traces that had fewer than four associated station triggers. Traces are in network-day directories named as follows: R076.01/ES25_97.076.23.56.32.7442.1 where R076.01 contains data for Julian day 076, data stream 1, and ES25_97.076.23.56.32.7442.1 is the SEGY trace file for station ES25, REF TEK serial number 7442, channel 1, beginning at 97.076.23.56.32. (7231.34 MB untarred) To read a specific file from tape, use the UNIX mt command to position the tape drive to the desired file and use the tar command to extract the directory or file. SEGY Header Information ----------------------- The PASSCAL SEGY trace headers include the station name, location, sensor serial number, and SEED channel name in addition to the standard values describing trace start time, trigger time, sampling, and REF TEK serial number. Station locations are expressed in seconds of latitude and longitude (1 degree is 3600 seconds); elevation is in meters. These locations are averages of the GPS positions reported in the log files. Elevations at Cerro Prieto are below sea level, however, the elevations have a larger uncertainty than the latitude and longitude. Earthquake times and locations are unknown. There is no PASSCAL SEGY header value for sensor model type, however, traces recorded using L22 sensors have SEED channel names of EP{ZNE}, while the CMG-40T has the channel names EH{ZNE}. Channels 1, 2 and 3 are named Z, N, and E respectively. The PASSCAL SEGY format is described on the IRIS PASSCAL website at http://www.passcal.nmt.edu/NMT_pages/Software/segy.shtml.