Cajon Pass Borehole Seismic Recording - Instrumentation Data Submitted to IRIS October 2020 Rachel Abercrombie University of Southern California (Now at: Boston University, USA; Email: rea@bu.edu) 15 October 2020 This document describes the Cajon Pass deep borehole seismic recording, including the instrument responses, timing and other relevant information concerning the earthquake data recorded during this project. The results have been published in a number of papers which also include further information about the experiment and instruments used. Description of Experiment Deep seismic recording began at Cajon Pass in August 1991 when Peter Leary and Derek Manov (University of Southern California) installed a triaxial set of geophones at 2.5 km depth, Phase I. These instruments continued to record until August 1993, and a surface instrument was also deployed during 1992. The data from first deployment (Phase I) is included here. The recording was performed using a succession of borrowed data loggers on short term loans, as the deep instrument remained functional for longer than was originally anticipated. One component did gradually fail during the course of the experiment, and all were deteriorating towards the end. The deep instrument was removed from the hole in August 1993. Phase II recording with instruments at the surface, 300 m, 1.5 and 2.9 km began in November 1993 and the instruments were withdrawn in August 1995. Phase II was performed using IRIS instruments and was previously archived as IRIS DATA SetÉ. (Julian days 326 1993 to 286 1994). Here I deposit the original data recorded during Phase I. The Cajon Pass Scientific Drillhole (also known as the DOSECC hole) was drilled in the late 1980Õs to investigate the state of stress and heat flow along the San Andreas Fault. Volume 15 of Geophysical Research Letters (August 1988) and volume 97 of Journal of Geophysical Research (April 1992) contain selections of papers related to the borehole. The top of the hole is at 34.3144?N, 117.4772?W, 960 m above sea level. Description of Data The data are in the form of RefTek SEGY triggered event files, all 60 s long. No timing corrections have been implied to any of the data. For most of the time, there was no external clock. Various omega clocks were used, some with more success than others. The absolute time can thus deviate by several seconds from the correct time, but the relative timing of the recorded channels is accurate. Triggering always took place on the borehole sensor and so false triggers only arise from electronic problems (e. g. water in the connectors) and not from external noise sources. All triggers have been kept. These data have many problems due to the difficulties and limitations of recording on an instrument so deep, at such a high temperature (105C) on an extremely small budget, at an accessible site prone to vandalism and theft. The best quality data downhole are probably the downhole vertical channel (usually channel 4), despite the high level of 60 Hz noise. Abercrombie gratefully acknowledges salary and technical support from the Southern California Earthquake Center, and University of Southern California, as well as many loans of equipment. The log files are included with all the information concerning timing, and sample rates and gains. The triggering ratio (ST/LT) was varied to record as many events as possible, but not to fill the disk between visits. The ftp to IRIS includes (a) the data (seismograms and log files), (b) an event catalogue (cp11.cat) in the format described below, and (c) 2020_PhaseI-CAJP.README (which contains this text in ascii), and2020_PhaseI-CAJP.README.RTF (which contains this text in RTF format). Significant Earthquakes During Recording Period 1992 April 22 M6.1 Joshua Tree earthquake 1992 June 28 (JDay 180) M7.3 Landers earthquake The deep instrument recorded both mainshocks, although it clipped, and many aftershocks. Bibliography of Work to Date from this Experiment Abercrombie, R. E. and Leary, P. C. (1993) Source parameters of small earthquakes recorded at 2.5 km depth, Cajon Pass, southern California: implications for earthquake scaling, Geophys. Res. Lett., 20, 1511-1514. Abercrombie, R. E. and Mori, J., 1994, Local observations of the onset of a large earthquake: 28 June 1992, Landers, California, Bull. Seism. Soc. Am., 84, 725-734. Leary, P. C. and Abercrombie, R. E. (1994a) Frequency dependent crustal scattering and absorption at 5 - 160 Hz from coda decay observed at 2.5 km depth, Geophys. Res. Lett, 21, 971-974. Leary, P. C. and Abercrombie, R. E. (1994b) Fractal fracture scattering origin of S wave coda: spectral evidence from recordings at 2.5 km, Geophys. Res. Lett, 21, 1683-1686. Abercrombie, R. E. (1995a) Earthquake locations using single station deep borehole recordings: implications for microseismicity on the San Andreas fault in southern California, J. Geophys. Res., 100, 24003-24014. Abercrombie, R. E. (1995b) Earthquake source scaling relationships from -1 to 5 ML using seismograms recorded at 2.5 km depth, J. Geophys. Res., 100, 24015-24036. Abercrombie, R. E. (1996) The magnitude-frequency distribution of earthquakes recorded with deep seismometers at Cajon Pass, southern California, Tectonophysics, 261, 1-7. Manov, D. V., Abercrombie, R. E. and Leary, P. C. (1995) Reliable and economical high temperature deep borehole seismic recording, Bull. Seism. Soc. Am., 86, 204-211. Abercrombie, R. E. (1997) Near surface attenuation and site effects from comparison of surface and deep borehole recordings, Bull. Seism. Soc. Am., 87, 731-744. Adams, D. A. and R. E. Abercrombie (1998). Seismic attenuation at high frequencies in southern California from coda waves recorded at a range of depths, J. Geophys. Res., 103, 24257-24270. Abercrombie, R. E., (1998), A summary of attenuation measurements from borehole recordings of earthquakes: the 10 Hz transition problem, Pure Appl. Geophys., 153, 475-487. Abercrombie, R. E. and Rice, J. R., (2005), Can observations of earthquake scaling constrain slip weakening?, Geophys. J. Int., 162, 406-424. Shearer, P. M., and R. E. Abercrombie (2020) Calibrating Spectral Decomposition of Local Earthquakes using Borehole Seismic Records - Results for the 1992 Big Bear Aftershocks in Southern California, Journal of Geophysical Research-Solid Earth. CAJON PASS PHASE I - SUMMARY Dates and times in California Local Time (all recording in UT). Date Notes 1992 106 April 15 (Start of reasonably reliable recording) Surface instrument buried in shallow hole in dirt near top of borehole. L22D (N arrow = east facing) RefTek installed to record 6 channels: Surface = channels 1,2,3 250 samples/s 2.5 km = channels 4 (Z), 5 (H1), 6 (H2) 500 samples/s 1992 182 June 30 Disk filled with Landers aftershocks. 1992 183 July 1 Restarted recording 1992 203 July 21 Disk filled with Landers aftershocks, so some days recording missed. 1992 208 July 26 RefTek needed for Landers aftershock deployments so recording temporarily ended. 1992 September 2 Borrowed RefTek (SN 499) from UCLA and restarted recording. Downhole only. Solar panel now used so no need to change batteries so often. 1992 315 November 10 Restarted uphole recording as well as 2.5 km 1992 329 November 24 Found recording had stopped on Day 321. Restarted recording. 1992 338 December 3 Solar panel stolen since last visit. Last recorded event day 337. 1992 349 December 14 Found RefTek under water. No recording days 343-350. 1992 350 December 15 Recording restarted 1992 363 December 28 RefTek found flooded. 1993 027 January 27 Recording restarted with Reftek in T-Hut on loan from Carl Petersen of CDMG, Sacramento. Recording downhole only. Gain increased and sampling rate increased to 1000 s/s 1993 February 4 Reftek disk had filled so some days recording lost. 1993 188 July 7 Last day of data. T-hut was discovered broken into and the Reftek stolen on 19 July. 1993 August 21 Deep instrument package removed from hole. Event Catalogue All earthquakes recorded at 2.5 km, up to and including day 180, 1992 (the Landers earthquake), have been picked and catalogued and are included on the tape in the file jp11.cat A description of the cataloguing process is given in Abercrombie (1996). No digital catalogue was made for the later part of the experiment. Format: format i4,1x,i3,1x,i3,1x, i2,i2,f6.3,1x,2(i6,1x),3(i5,1x), read iyr, jday, itrig, th,tm,ts, Pt,St, Az,Ah1,Ah2, -- a6,1x, i6,1x, a1, f3.1, a30 -- polarity, coda, comm1, mli, comment Explanation: iyr Year of event jday Julian day of event itrig Number of trigger at 1.5 km on jday th Hour of event trigger (note that timing is not always correct - see above) tm Minute of event trigger ts Second of event trigger Pt P time pick measured from trigger time (milliseconds) St S time pick measured from trigger time (milliseconds) Az Max amplitude on vertical component (counts) Ah1 Max amplitude on 1st horizontal (h1) component (counts) Ah2 Max amplitude on 2nd horizontal (h2) component (counts) polarity 3 component P and S polarities (P on Z,H1,H2, S on Z,H1,H2) up:down = +:- for P; *:/ for S. coda Time at which coda on H1 reaches approximately 3 times background (milliseconds after trigger time) comm1 M - prefix to magnitude from SCSN mli SCSN magnitude where available (some events may be missed) comment Various comments - includes SCSN CUSPID if available. Also used to identify ÒringersÓ - strange high frequency events which may be nearfield radiation or something else (e. g. cable slip). No S is seen for these events. Table 1: Cajon Pass Instrument Characteristics. Depth Operation Dates Gain Sample Instrument Vertical Horizontal 1 Horizontal 2 Polarity Comments Rate (/s) G (V/in/s) fc (Hz) D G (V/in/s) fc (Hz) D G (V/in/s) fc (Hz) D Surface April 1992 - July 19923 8 250 L22-D 2 Hz 0.86 2 0.46 0.86 2 0.46 0.86 2 0.46 Z = up, H1 = W (?3?), H2 = N (?3?) General instrument specifications. Accurate timing relative to 2.5 km, not absolute time. 2.5 km April 1992 - August 19933 5126 5006 L-15LA-TW-HT 10 Hz 0.65 10 0.7 0.65 10 0.7 0.65 10 0.7 Z = up, H1 = 18? (?3?), H2 = 72? (?3?)7 General instrument specifications. No absolute time (accuracy ? 5 s) Surface November 1993 - August 19954 8 250 L22-D 2 Hz 0.968 2.533 0.433 0.960 2.064 0.458 0.988 2.060 0.495 Z = up, H1 = N, H2 = E Measured in situ2 300 m November 1993 - August 1995 32 500 L1-B 4.5 Hz 4.765 4.114 0.945 5.105 4.297 0.725 4.346 4.423 1.284 Z = up, H1 ~ -10? (?10?), H2 ~ -100? (?10?)8 Measured in situ 1.5 km November 1993 - August 1995 512 1000 L-15LA-TW-HT 10 Hz 0.615 10.977 0.583 0.602 10.593 0.597 0.617 11.211 0.606 Z = up, H1 ~ 142? (?5?), H2 ~ 50? (?5?) Measured in situ 2.9 km November 1993 - August 1995 512 1000 L-15LA-TW-HT 10 Hz 0.526 10.471 0.565 0.551 10.309 0.534 0.513 10.111 0.535 Z = up, H1~ 115? (?10?), H2 ~ 25? (?10?) Measured in situ Granite9 August 1994 - September 1994 8 250 L22-D 2 Hz 0.876 2 0.72 0.870 2 0.72 0.873 2 0.72 Z = up, H1 = N, H2 = E G from measured geophone coil resistances Notes: 1. All Instruments (Mark Products Geophones) are run on 16 bit RefTeks, with full scale ?3.75 V. G is the generator constant, fc is the geophone corner frequency and D is the damping factor. 2. In situ calibration in May 1994 and June 1995 using the technique developed by Rodgers et al. (1995). The calibrations showed negligible changes in the response of the geophones, after 11 months at elevated temperatures, within the errors of the calibration system (in this case < 5%, A. Martin, pers. comm.) 3. Phase I operation. The 2.5 km instrument was installed in August 1991 but recording prior to April 1992 was in short periods using a USC made recording system. Down time in April due to water problems in the recording system. No RefTek datalogger was available from 26 July to 2 September 1992 due to the Landers aftershock deployments, and so no recording. Downtime during winter on account of water getting into RefTeks as site flooded following rain. All data was recorded on field exabyte tapes. Then it was loaded onto the SUN using ref2segy, and the RefTek SEGY files were backed up in duplicate using TAR onto exabyte tapes. In recent years there was space to store this (now relatively small) data set online. 4. Phase II operation. A summary of the second phase of recording follows. 5. All data was recorded on field exabyte tapes. Then it was loaded onto the SUN using ref2segy, and the RefTek SEGY files were backed up in duplicate using TAR onto exabyte tapes. These data were compressed and loaded onto one DAT tape to send to IRIS. 6. Gain increased to 2048 and sample rate to 1000 between 27 January and 7 March 1993. 7. Determination of 2.5 km horizontal orientation in Abercrombie (1995a). Note North = 0?, East = 90? etc. 8. Borehole horizontal orientations in Phase II are estimated by the same method described in Abercrombie (1995a). The angles are preliminary using only a small number of earthquakes. 9. The ÒgraniteÓ instrument was installed on hard granite with plaster of Paris. Location: 34.3113?N, 117.4625?