Joshua Tree Aftershock Data
- Network Code: XA
- Experiment duration: 1992-04 to 1992-06
- Number of events: 9580
- Prinicpal investigators: Adam Edelman, Frank Vernon
- Dataless SEED volume currently unavailable. Please visit the IRIS DMC
The Ml 6.1 Joshua Tree earthquake of April 23rd, 1992 04:50 GMT occurred at 33.961°N, 116.318°W approximately 8 km northeast of the southern San Andreas fault and about 20 km south of the Pinto Mountain fault [More information]. The primary aftershock activity occurred in a band extending from 33°N 50.0', -116°W 16.0' to 34°N 15.0', -116°W 19.0'. Southern California Earthquake Center (SCEC) personnel responded within 24 hours by installing portable instruments to record the aftershock sequence. Over 6000 aftershocks were recorded between April 25 - May 31 by up to 11 stations. 3174 were also recorded and located by the Southern California Seismic Network (SCSN) and associated with the portable records. These data have had all known timing errors corrected, both P and S-phases picked, and are available from the SCEC Data Management Center at Caltech and in SEED format from the IRIS Data Management Center at the University of Washington.
Within the first 48 hours following the main shock, SCEC personnel installed six portable stations, with the maximum of eleven simultaneously recording stations operating within the first week. Five of the twelve instruments were deployed within the Joshua Tree National Monument area, with the remaining seven located in the vicinity of Desert Hot Springs. The station locations are shown in Figure 1. Over 3 Gb of raw data were acquired during the 40 day deployment. A time line showing the recording status of each station throughout the deployment is shown in Figure 2, indicating an excellent level of data recovery.
The equipment consisted of Refraction Technology (Reftek) 72A-02 16-bit dataloggers recording either Mark Products L-22 velocity sensors, Guralp CMG3t broadband velocity sensors, Kinemetrics FBA-23 accelerometers or both L22 and FBA sensors. The total system response for each instrument parameter configuration has been calculated and can be used to correct for instrument characteristics. Figure 3 shows the normalized velocity and acceleration response for four of the instrumentation configurations.
Station locations were determined by a differential GPS survey providing accuracy to 1 meter (Scott et al., 1994).
Data from the field were copied to 8 mm Exabyte tape with a Reftek field Exabyte drive. The data were then read on a Sun computer where it was converted to SEGY format and the datalogger state of health logs were generated. All known timing errors were corrected utilizing software from the PASSCAL Instrument Center at Lamont Doherty Earth Observatory (PIC). Table 1 shows the time shifts applied to each station in order to correct for those errors.
A time based event association was then done with software from the PIC which grouped all triggers that occurred within a specified time window. All SEGY data were then converted to CSS 3.0 and both P and S phases were picked by hand. An association with the SCSN catalogue was then done utilizing software from the University of Colorado which associates predicted arrivals with the actual phase picks. The data were then converted to the SCEC database format and shipped to Caltech for integration into the CUSP system. The data was also converted into SEED format and delivered to the IRIS DMC in Washington state.
A problem was discovered within the SCEC database that affecled the sensor channel polarities for some stations. Data that were retrieved prior to February 8, 1995 may be affected by this bug and should be replaced with the data currently on-line at Caltech.
The data set consists of 3174 events, all of which are associated with an SCSN catalogue location. The distribution of aftershocks is shown on the map in Figure 1. The magnitude distribution is shown in the upper part of Figure 4, indicating that the majority of events fall between MILS and Ml 3.5. The lower part of Figure 4 is a histogram showing the number of events recorded versus the number of stations recording each event. Travel time residuals were calculated for each station while the event association was done. This gives us a qualitative view of the accuracy of the data timing. Figure 5 shows the travel time residuals for both P and S-phase associations for each station. The residuals are essentially zero for each station which indicates the high quality of data timing in this set. Figure 6 shows two examples of typical events recorded by the portable stations. The upper event in the figure is one of the larger aftershocks (Ml 4.74) which was recorded by nine of the stations.
Several people contributed to the data acquisition, processing and preparation of this product. Personnel from the California Institute of Technology, the University of California at San Diego, the University of California at Santa Barbara, and the University of Southern California participated in the work. Aaron Martin and Craig Nicholson from UCSB played key roles in the field deployment and initial data processing, and Dave Johnson from Caltech also contributed greatly to the field deployment. Katrin Hafner from Caltech, and Dan Shaw from UCSD played important roles in finishing the data processing. Software support was provided by personnel at the PASSCAL Instrument Center at Lamont Doherty Earth Observatory and the JSPC at the University of Colorado at Boulder. Funding from SCEC fund #40140A provided support for the data processing.
- Scott, J., Hauksson, E., Kanamori, H., Mori, J., 1994, Global Positioning Re-Survey of Southern California Seismic Network Stations, Bulletin for the Seismological Society of America
|Station||Shift Applied (ms)||Comments|
|AQUA||-70 – -331, linearly increasing||Linear shift applied to correct for known clock drift from 92116:0092119:18|
|BRCC||12 – 131, linearly increasing||Linearly increasing shift applied to correct for known clock drift from 92116:00 – 92128:23|
|COVF||No shifts applied||No corrections necessary.|
|DWSR||234||Static shift to correct for Omega clock jerk from 92119:23 - 92120:00|
|EDCl||No shifts applied||No corrections necessary.|
|EDCY||No shifts applied||No corrections necessary.|
|EDOM||11435,10000 – 10029, 1 – 55 linearly increasing, -175||Shifts applied to correct for known clock drifts:
11435 from 92116:00 – 92121:11
10000 &ndash 10029 linearly increasing from 92121:11 – 92125:17
1 &ndash 55 linearly increasing from 92125:20 – 92133:30 -175 static shift between 92140:0092140:19
|HDVL||23000,6400||Static shift to correct for Omega clock jerks: 23000 from 92116:03 – 92133:23 6400 from 92133:23 – 92140:23|
|KEYV||14||Static shift to correct for Omega clock jerk from 92119:22 – 92119:23|
|LMVR||-5000||Static shift to correct for Omega clock jerk from 92116:00 – 92116:02|
|SDCE||No shifts applied||No corrections necessary.|
|UCVF||-4000,-113||Static shifts applied to correct for Omega clock jerks: -4000 from 92116:18 – 92117:03 -113 from 92118:01- 92118:02|
|AQUA||1992116||1992155||33.932||-116.3802||0.458||Colorado River Aqueduct, Desert Hot Springs, Calif||ss||–||–||–|
|BRCJ||1992116||1992155||34.069||-116.3923||1.233||Black Rock Campground Joshua, Joshua Tree National||ss||–||–||–|
|COVF||1992119||1992145||34.0302||-116.3482||1.638||Covington Flats, Joshua Tree National Monument, Ca||ss||–||–||–|
|DWSR||1992119||1992151||33.7658||-116.5461||0.162||Desert Water South Reservoir, Palm Springs. Calif.||ss||–||–||–|
|EDC1||1992119||1992147||33.9166||-116.3266||0.48||East Deception Canyon 1, Sky Valley, Calif.||ss||–||–||–|
|EDCY||1992124||1992145||33.9038||-116.3364||0.377||East Deception Canyon, Sky Valley, Calif.||ss||–||–||–|
|EDOM||1992116||1992147||33.8696||-116.4298||0.454||Edom Hill, Indio Hills, Calif.||ss||–||–||–|
|HDVL||1992116||1992147||34.0098||-116.1685||1.261||Hidden Valley, Joshua Tree National Monument, Cali||ss||–||–||–|
|KEYV||1992119||1992141||33.9262||-116.1816||1.515||Key's View, Joshua Tree National Monument, Calif.||ss||–||–||–|
|LMVR||1992116||1992119||33.9929||-116.5241||0.406||Little Morongo Valley Ranch, Desert Hot Springs, C||ss||–||–||–|
|SDCE||1992116||1992155||33.9347||-116.4043||0.416||Smith Desert Country Estate, Desert Hot Springs, C||ss||–||–||–|
|UCVF||1992116||1992155||34.0108||-116.3057||1.441||Upper Covington Flats, Joshua Tree National Monume||ss||–||–||–|
URL: http://eqinfo.ucsd.edu/deployments/portable_aftershock_studies/joshua_tree.php [Last updated: 2015-10-22 (295) 22:24:32 UTC]