Landers/Big Bear Aftershock Data

Summary

Introduction

A collaborative study to record aftershocks was undertaken by several Southern California Earthquake Center (SCEC) institutions following the June 28, 1992 Landers and Big Bear earthquakes. The M7.6 Landers earthquake occurred at 04:58 PDT approximately 6 miles north of Yucca Valley along the southern extension of the Johnson Valley fault. The earthquake produced over 70 km of ground rupture, with cumulative right-lateral offsets of 3 to 6.5 m along segments of the Homestead Valley, Emerson Lake, and Camp Rock faults, all of which were involved in the sequence. The primary aftershock activity occurred in a narrow band from 33.6°N, -116.2°W north to 34.5°N, -116.6°W, with a separate cluster at 35.0°N, -117.0°W. The M6.5 Big Bear earthquake occurred at 08:04 PDT approximately 35 km west of the Landers epicenter in the San Bernadino Mountains, involving left-lateral slip on a fault that strikes N45OW and dips 70° SE. The Big Bear aftershocks occur over an area about 30km long, extending northeast from 34.4°N, -116.6°W

Personnel from the California Institute of Technology (Caltech), San Diego State University (SDSU), the University of California at Santa Barbara (UCSB), the University of California at San Diego (UCSD), and the University of Southern California (USC) participated in the installation and maintenance of the portable stations. Within 12 hours, four portable instruments were installed and started recording data, and an additional 18 were up and running within 48 hours. Approximately 10 Gb of raw data from thirty-one individual stations were acquired in the 2 months following the main shocks.

The task of processing these data was undertaken by UCSD and consisted of three main steps:

In addition, all event header information and phase arrival data have been converted into the SCEC database format for this release of data, which contains all altershocks of magnitude 4.0 and greater or recorded at five or more of the portable stations and have an unambiguously associated Caltech CUSP ID.

Contributors

The following participants collected or provided data for this product:

Field deployment

The initial response to the earthquake involved the mobilization and deployment of all available equipment to the main shock areas. The first day of deployment was accomplished with minimal coordination between the field teams due to the difficulty of communications and the delays inherent in processing and evaluating regional network data in such an extreme situation. The first portable stations were set up in the regions of the Landers and the Big Bear epicenters. By the end of the second day better communication procedures were in effect and all the SCEC seismic field teams were coordinating their efforts to maximize the coverage of the aftershock zones.

Communications by fax and by phone with Southern California Seismic Network personnel provided necessary information to help make decisions about the locations where new stations should be deployed to complement existing network coverage and known portable installations. Within 12 hours of the Landers earthquake there were 4 operational portable stations and in the following 36 hours an additional1B stations were installed, including the LDEO portable stations that were installed concurrently in the eastern Coachella Valley. The station locations (Figure 1), and have been calculated to 1 meter accuracy with the use of differential GPS (Scott et af., 1994). Table 1 shows the station locations, number of triggers, and the range of epicentral distances, Table 2 shows the station equipment particulars, including recording parameters.

The first stations were deployed using equipment which had been initially located in southern California. By the second day additional equipment was received from the IRIS PASSCAL Instrument Center and from the USGS. There were five primary station configurations deployed. Three of these configurations (Figure 2) were high frequency stations using Mark Products L22-D seismometers, andlor Kinemetrics FBA-23 accelerometers recorded on either Reftek R172A-02, or Kinemetrics SSR-1 dataloggers. The remaining configurations (Figure 3) used either Streckeisen STS-2 or Guralp CMG-3T broadband seismometers with Reftek R172A-02 dataloggers. The broadband sensors were much more difficult to install and maintain due to their sensitivity to the environment and, in particular, to temperature gradients. But with proper siting and insulation it was possible to acquire high quality data from these sites. Each station was powered from 12 V batteries which were either exchanged during maintenance or charged in place. The charging was done by a solar panel or by a local 120 V AC source. Timing at all stations was based on the OMEGA time system.

Both the REF TEK R172A-02 and the Kinemetrics SSR-1 (SSR-1) dataloggers utilize 16-bit AID convertors. The R172A-02 was run in event trigger mode at either 250 or 100 s/s. The SSR-I was run in event trigger mode at 200 s/s. Both loggers employed an STA/LTA (short term to long term average) triggering algorithm.

The LDEO Coachella Valley stations recorded Kinemetrics SH-1 and SV-I velocity sensors, and Terra Tech FBA accelerometers with Kinemeterics PRS-4 dataloggers. Further information regarding the LDEO installations is available from Ned Field at the LDEO.

The total system response for each instrument/parameter configuration has been calculated and can be used to correct for instrument characteristics. Figures 4, 5, 6, 7, 9, 10, 11, 12, 13 show the normalized velocity and acceleration response. Amplifier gain and additional calibration information can be retreived from UCSD.

Twenty-one stations were operational by July 11, two of which were moved during the experiment to get better coverage of the northern aftershocks. After nearly three weeks of operation the network was reduced to 16 stations and by early August a skeleton array of 6 stations was left until early September. After the network was configured for 16 stations the field station visits were reduced from nearly daily down to a weekly or bi-weekly schedule. Figure 14 shows the status of each station throughout the experiment including the time periods that data were recovered along with the sensors that were deployed.

Sensor placement for each station was dictated by the local geology. The following stations had sensors installed directly on hard rock outcroppings of granitic composition: BN]I, EORD, ERWL, FORF, GRAV, HILL, IRON, LPMA, UCVF, UGGP, and YKNF. Most of these sensors were buried with loose gravel. The stations FIRE, GPOE, GRAC, LADY, RIMR, and VVST were located in very shallow sediments and were buried approximately 1 ft while BRDO and EDC2 were located in sedimentary rock. Station VlPC had its 515-2 mini-vault plastered directly to a hard-rock granite outcrop, and was covered with fiberglass insulation. The 515-2 mini-vault at JFRG was plastered to a slightly weathered granite outcrop, covered with fiberglass insulation and buried under a layer of soil. Station BRCC was installed inside a Joshua Tree Monument campground building with its 515-2 mini-vault plastered directly to the concrete foundation. The building was located on weathered granite. Station CG1S was located in a mine tunnel in hard rock.

Data processing

The processing scheme required several steps: raw data retrieval followed by formatting, quality control, timing corrections, and event association. A Sun Sparc field computer was set up in a motel room several days after the main shocks. Much of the data reformatting, quality control and timing corrections were performed on this field computer. The computer was operated for about three weeks and data collected afterwards were processed at one of the participating institutions.

Initially, a REFTEK Exabyte drive was used to dump the data at each station, but it was found to be more reliable to exchange hard discs and copy data via the SCSI bus on a Sun Sparc station. After the raw data were downloaded to disk, TAR backup tapes were made. Next the data were converted to PASSCAL SEGY format and reviewed using PASSCAL's quick look program PQL to evaluate the station performance. Data recorded on SSR-ls were brought back to SDSU, then copied to a Sun Sparc station and converted to PASSCAL SEGY format.

Errors in timing were also corrected at this point. The common timing errors that were present in the raw data resulted from improper leap second settings and unlocked Omega time clocks. Unfortunately, not all the RT72A-02 had the same firmware revisions. Firmware revisions 2.44, 2.45, and 2.46 were all used and each has a different leap second setting. To further complicate matters, an additional leap second was inserted on June 30, two days into the experiment. The timing shifts were accomplished by applying a shift to the trace start time via the TotalStatic field in the SEGY header using the program SEGYSHIFT.

The next step involved event association between the portable stations. This was accomplished by running the UCSB_TABLE and REAP programs. UCSB_TABLE creates a listing of event times, while REAP associates the data according to specified time and array parameters. Both the LDEO and SDSU datasets were then associated with the P ASSCAL dataset based on event time windows. At this stage all data meeting certain time criteria were organized into a sequence of events, and both P and 5 phases were picked. In order to determine event locations and magnitudes, two methods were used to associate the portable station records with the SCSN catalogue. An initial event-time association was performed, utilizing an ORACLE relational database, which correlated SCSN origin times and the events generated by REAP. This did not create a unique association so we utilized the program dbassoc_arrivals (written by Dan Quinlan at the University of Colorado) which associates predicted arrivals from an origin table using the IASPEI91 travel time tables and the actual P and S phase picks. Due to the high level of activity during the first few days of the deployment, approximately 10% of the records contain more than one event which resulted in ambiguous associations. Some of these problems also occured when the SCSN catalogue contained multiple locations within a small time window leading to more than one location for a single portable event. These records will be reviewed and re-associated at a later date. Finally, all event header information and phase arrival data were converted from CSS 3.0 format to the SCEC database format (Appendix 1). The data will also be converted to SEED format with all response information included, and be available from the IRIS Data Management Center at the University of Washington.

Data

This release of data comprises 2345 events recorded at 5 or more stations, each having an associated SCSN CUSPID. Figure 15 shows the distribution of these aftershocks. Figure 16 shows magnitude distribution, indicating that the majority of events fall between MI1.5 and MI4.5, and Figure 17 shows a histogram of number of events recorded versus number of stations. Figure 18 shows the range of magnitude versus epicentral distance, and Table 3 shows initial SCSN locations of all Ml4.0 and larger events.

For the majority of the data, the timing corrections that were applied were necessary to correct for known offsets due to leap second discrepancies, and resulted in accurately timed data. There were some stations whose time clocks were either faulty, or were not reliably synchronized to the Omega transmitting stations. Station UCVF never locked on to an Omega transmitter, and it is apparent that the timing drifts an unknown amount (+/-10 seconds) throughout the data set. Station UGGP has unreliable timing for days 194-198 due to frequent lock and unlock cycles of the Omega timeclock. These data were left uncorrected, instead of applying estimated shifts based on phase arrivals. Table 4 shows the time shifts that were applied to the data to correct for the known discrepencies. To further examine any systematic timing errors, travel time residuals have been calculated with the dbassoc_arrival program, Figure 19 (a, b, c, d) shows these residuals for each station for all arrivals within 4 seconds of a predicted arrival. Figure 20 shows the residuals for stations UCVF and UGGP during periods of unreliable timing.

The data set consists of a wide range of earthquakes, from records with S-P times of less than 0.5 seconds, to events with anomalously low frequency waveform characteristics throughout the record, as well as many co-located events with similar magnitudes. Figure 21 shows the vertical traces of an event in the Big Bear region with an epicentral distance of approximately 150 meters from station ERWL. Figure 22 shows the vertical traces of an event recorded by 14 portable stations as well as 4 TERRAscope stations displaying low frequency characteristics.

In addition to the data contained in this product, both the USGS and UCSB have data sets containing aftershocks from the Landers area. UCSB deployed two 5-element arrays of Kinemetrics SSAZ accelerographs, and has data available via ftp (contact Jamie Steidl at UCSB for further information). The USGS deployed 34 GEOS instruments recording both L-22 and FBA-23 sensors including 5 that were in operation at the time of the main shock. The resulting data set consists of 484 events that were recorded between May 18 and August 23, 1992 (Hough, S. E. et al., 1993).

Discussion

This aftershock experiment collected the largest amount of data of any RAMP to date, approximately 1O Gbytes from more than 13,000 events. Considering that the mainshocks occurred on a Sunday morning, and that field teams each had a minimum of 3 hours travel time, it is quite remarkable that the first event recorded on multiple portable stations occurred less than 12 hours after the Landers mainshock. The equipment support by the IRIS PASSCAL Instrument Center, the USGS Branch of Earthquake and Landslide Hazards, and the Rocky Mountain Front Experiment was essential for the maximum deployment of 24 simultaneously recording stations.

After reviewing the field operations for this experiment, it is clear that there are some essential procedures which should be followed in the future to maximize data recovery and minimize redundant effort. The most important component for a successful experiment is a communications plan. The field personnel need a dedicated contact point at the nearest regional seismic network center which acts as a message center. This will allow field teams to coordinate their efforts when they are working in different geographical areas. The contact point should also be responsible for providing the most recent updates on the aftershock activity. This information is critical for field teams to decide where to deploy the next stations. Due to the difficulties of getting to a working telephone, particularly in remote areas like the Landers aftershock zone, the contact point should be constantly manned for the first several days. During this experiment several members of the SCSN staff fulfilled this role. From the field side, it is important that all groups use this contact point until a local field headquarters can be established. Ideally, all field groups would have mobile radios, but the reality is that the pay phone will be the primary method of communications. Once the field headquarters is established then one person should be tasked with manning this post and that person should have the responsibility to coordinate field groups and maintain contact with the regional seismic center. In this manner the co-location of equipment with identical sensors can be avoided and stations can be distributed efficiently and adaptively in a dynamic situation.

The other important component is the establishment of a data processing computer at the field headquarters with an individual dedicated to managing the data as it returns. This is one of the most important elements of the field exercise since this allows quality control capability at the outset and allows initial data processing to proceed without delay. The quality control issues which must be addressed immediately are whether ail components are working and gains set correctly along with an evaluation of the time quality and accuracy. The field computer should have enough disk space to be able to load 2 days' data from the array from ail stations so that full event associations can be made. In the case of Landers at least 4 Gigabytes would have been needed. In this experiment a computer was not installed for several days and, in retrospect, having one would have improved the efficiency of the field operations as well as the overall data recovery. The initial volume of data was so large that the first order processing and quality control was not completed until months after the experiment was over. In fact, new data sets have surfaced as late as one year after the start of the experiment requiring association with the final data product.

There are several software areas which need development to improve the data processing scheme. The first is to incorporate an automatic phase picking algorithm which is appropriate for both broadband and short period data. This should be followed by a more sophisticated algorithm to associate arrival phases into events. The current algorithms are based purely on a time-based association which works well in a single event per trigger environment, but during Landers there were several thousand events associated by this algorithm which were actually multiple events. At the present time these are sorted out manually, yet many of these multiple event triggers could have been identified automatically. Once a proper set of arrivals are chosen then a standard location program could be used. The fundamental routines to solve these data processing problems exist now and are being prepared as a software package for future aftershock studies.

The final lesson learned from this experiment is the benefit of using short period seismometers, strong motion accelerometers, and broadband seismometers. During the first days it was extremely important to get stations operating quickly and this meant using short period sensors and accelerometers. Once the basic network was functioning, then the extra hour or two time investment for installing broadband sensors proved to be worthwhile and yielded recordings of previously unidentified seismic signals from local earthquakes, as seen in the low frequency signals present in Figure 21.

In the final preparation of this release, we encountered problems with ambiguously associated events affecting approximately 10% of the data. We plan to examine the phase data and re-associate these events with the SCSN, as well as location calculations for future release.

Acknowledgements

Several institutions contributed resources which helped us to complete this quality product. Art Lerner-Lam and Gene Humphrey promptly removed equipment from their Rocky Mountain Front experiment for loan to SCEC which enabled us to deploy the broadband stations. Tom Henyey and Leon Teng from USC loaned instruments from their Los Angeles Basin experiment which helped speed the deployment in the early stages. Personnel at the IRIS P ASSCAL instrument center and the USGS Branch of Earthquake and Landslide Hazards provided several stations worth of equipment. Danny Harvey and Dan Quinlin at the University of Colorado provided software and helpful discussions during the processing procedure. Personal communications with Sue Hough at the Pasadena branch of the USGS were helpful in obtaining information regarding their deployment and data set. Funding from SCEC fund #40140A helped support the task of maintaining the stations and processing the data.

References

Table 1. Station particulars, including station locations, minimum and maximum epicentral distances of recorded events, and the number of events recorded.
Station Latitude Longitude Elevation Min/Max Epi. Dist.(km) Events
BNJI 34.16248 -116.32100 827 2.35/274.42 2052
BRCC 34.07209 -116.39146 1207 0.33/277.76 2490
BRDO 33.82960 -116.14899 483 10.81/244.85 951
CGTS 34.95141 -116.86389 694 3.36/128.30 323
EDC2 33.91662 -116.32661 480 1.27/262.75 803
EORD 34.65607 -116.71799 1160 3.38/342.89 2252
ERWL 34.23493 -116.79843 2102 0.15/428.56 1674
FIRE 34.04858 -116.57799 749 15.22/33.14 9
FIR2 33.70810 -116.21440 -3 n/a 93
FORF 34.08331 -116.92047 1596 1.53/441.07 1330
FRED 33.68810 -116.25620 6 n/a 164
GOLF 33.68120 -116.27120 9 n/a 76
GPOE 34.42274 -116.71687 894 5.25 /366.59 1505
GRAC 34.26680 -116.38818 913 0.57/394.99 1988
GRAV 34.18700 -116.71979 2454 3.53/248.49 1699
HILL 3436135 -116.45415 891 0.66/87.87 68
IRON 34.61667 -116.56712 1152 1.01/236.89 1433
JEAN 33.70060 -116.23210 0 n/a 57
JFRG 34.04566 -116.62153 862 5.25 /184.27 1708
LADY 34.13062 -116.31390 811 5.82/57.40 54
LPMA 34.36031 -116.41921 733 1.18/384.41 2404
RIMR 34.18646 -116.46342 1099 0.23/44.77 251
ROKE 33.74500 -116.09960 244 n/a 110
ROKN 33.70210 -116.30060 43 n/a 8
ROKW 33.66720 -116.28390 9 n/a 167
UCVF 34.01077 -116.30596 1441 1.21/254.17 743
UGGP 34.74988 -116.66058 857 6.01/151.36 1110
VIPC 34.01772 -116.19027 1246 8.37/294.46 1644
VVST 34.35963 -116.57893 912 5.06/593.97 2782
YKNF 34.20749 -116.44573 1094 0.38/398.63 3055
Table 2. Station particulars, including deployment duration, sensor, logger and recording parameters.
Station Deployment Sensor Datalogger Sample Rate (s/s) Gain (db)
BNJI June 29 - July 25 FBA-23, L-22 RT72A-02 250 0.0, 18.0
BRCC June 30 - Sep 02 STS-2 RT72A-02 250 0.0, 18.0, 30.0
BRDO July 01 - July 08 FBA-23, CMG3t RT72A-02 100 0.0
CGTS July 08 - July 24 FBA-23, CMG3t RT72A-02 100 0.0
EDC2 June 30 - July 24 FBA-23, CMG3t RT72A-02 100 0.0
EORD June 30 - Sep 02 FBA-23, L-22 RT72A-02 250 0.0, 18.0
ERWL June 29 - July 18 FBA-23, L-22 RT72A-02 250 0.0
FIRE June 28 - July 07 FBA-23 KIN SSR-1 200 0.0, 45.6
FIR2 July 01 - July 08 SH-1, SV-1, FBA PRS-4 100 X
FORF June 29 - July 18 FBA-23, L4-C RT72A-02 250 0.0
FRED July 01 - July 10 SH-1, SV-1, FBA PRS-4 100 X
GOLF July 05 - July 10 SH-1, SV-1 PRS-4 100 X
GPOE June 30 - July 25 L-22 RT72A-02 250 0.0,18.0
GRAC June 29 - July 25 FBA-23, L-22 RT72A-02 250 0.0, 18.0
GRAV June 29 - July 18 FBA-23, L-22 RT72A-02 250 0.0
HILL June 28 - Aug 07 FBA-23 KIN SSR-1 200 0.0, 22.8, 45.6
IRON June 30 - Sep 02 FBA-23, L-22 RT72 A-02 250 0.0, 18.0
JEAN July 05 - July 10 SH-1, SV-1 PRS-4 100 X
JFRG Ju1y 02 - Sep 02 STS-2 RT72A-02 250 0.0, 18.0, 30.0
LADY July 07 - July 18 FBA-23 KIN SSR-1 200 0.0, 22.8
LPMA June 30 - July 25 FBA-23, L-22 RT72A-02 250 0.0, 18.0
RIMR June 28 - Aug 07 FBA-23 KIN SSR-1 200 0.0, 18.0, 45.6
ROKE July 01 - July 04 SH-1, SV-1, FBA PRS-4 100 X
ROKN July 09 - July 10 SH-1, SV-1 PRS-4 100 X
ROKW July 01 - July 10 SH-1, SV-1, FBA PRS-4 100 X
UCVF June 29 - July 25 L-22 RT72A-02 250 0.0, 18.0
UGGP June 29 - Sep 02 FBA-23, L-22 RT72A-02 250 0.0, 18.0
VIPC July 02 - Sep 02 STS-2 RT72A-02 250 0.0, 18.0, 30.0
VVST June 29 - July 25 FBA-23, L-22 RT72A-02 250 0.0, 18.0
YKNF June 29 - July 25 FBA-23, L-22 RT72A-02 250 0.0, 18.0
Table 3. All magnitude 4.0 and greater recorded by the portable stations.
Date Time Latitude Longitude Depth Ml
Jun 30,1992 00:06:8.605 34.1250 -116.4010 3.2200 4.37
Jun 30,1992 11:30:29.216 34.0930 -116.4170 11.6500 4.42
Jun 30,1992 12:14:49.729 34.0870 -116.4170 11.8600 4.19
Jun 30,1992 12:34:54.525 34.3220 -116.4480 4.5700 4.25
Jun 30,1992 13:05:36.449 35.6810 -117.6150 4.7400 4.57
Jun 30,1992 14:38: 11.598 34.0040 -116.3600 0.8500 4.88
Jun 30,1992 15:19:5.014 34.1710 -116.4090 0.3900 4.07
Jun 30,1992 15:20:8.801 34.2610 -116.7440 6.0000 4.17
Jun 30,1992 17:14:21.168 34.0640 -116.3740 0.0000 4.08
Jun 30,1992 17:26:30.169 34.6430 -116.6580 6.0000 4.41
Jun 30,1992 20:00:25.927 34.6420 -116.6540 6.0000 4.31
Jun 30,1992 20:05:6.587 33.9890 -116.3620 0.5700 4.08
Jun 30,1992 21:22:54.464 34.1300 -116.7340 11.9000 4.81
Jun 30,1992 21:49:0.285 34.0840 -116.9890 3.5600 4.43
Jul 1,1992 06:16:56.713 35.6780 -117.6130 3.6500 4.52
Jul 1,1992 07:01:49.186 34.0970 -116.3820 0.0100 4.33
Jul 1,1992 07:40:29.902 34.3310 -116.4630 8.2800 5.27
Jul 1,1992 10:29:47.660 34.9700 -116.9370 0.6400 4.28
Jul 1,1992 10:32:52.261 34.9730 -116.9360 0.1700 4.33
Jul 1,1992 17:07: 15.085 34.2740 -116.6920 4.7500 4.21
Jul 1,1992 17:45:46.850 34.2800 -116.6880 5.8900 4.49
Jul 1,1992 20:46:17.813 34.2750 -116.7300 1.0000 4.24
Jul 1,1992 20:53:56.765 34.2810 -116.7310 1.4300 4.03
Jul 2,1992 00:16:22.370 34.3130 -116.4430 6.8200 4.05
Jul 2,1992 22:25:29.094 35.6750 -117.6200 5.3200 4.28
Jul 3,1992 04: 15:50.370 34.2100 -116.7700 10.8700 4.15
Jul 3,1992 17:17:6.402 34.2620 -116.8950 7.6100 4.14
Jul 5, 1992 05:49:38.152 33.9450 -116.3990 3.2100 4.05
Jul 5,1992 10:55:43.290 35.0300 -116.9680 0.7800 4.62
Jul 5,1992 20:03:3.095 34.2980 -116.8040 3.0900 4.04
Jul 5,1992 21:18:27.135 34.5820 -116.3180 0.1100 5.38
Jul 5,1992 22:33:45.544 34.5830 -116.3040 0.0000 4.44
Jul 6,1992 12:00:59.188 34.0910 -116.3690 1.7000 4.39
Jul 6,1992 18:06:36.310 34.4570 -116.4760 0.4900 4.26
Jul 6,1992 19:41:37.894 34.0820 -116.3780 3.2700 4.43
Jul 7,1992 08:21:3.139 34.0690 -116.3820 3.2000 4.18
Jul 7,1992 22:09:28.337 34.3410 -116.4670 2.5400 4.42
Jul 8,1992 02:23:11.325 34.5750 -116.3350 6.0000 4.85
Jul 9,1992 01:43:57.608 34.2380 -116.8370 0.0100 4.87
Jul 10,1992 01:29:39.999 34.2320 -116.8460 0.5300 4.18
Jul 11,1992 18:14:16.148 35.2100 -118.0660 10.6900 5.67
Jul 20,1992 04:08:22.572 34.1980 -116.4320 0.4100 4.10
Jul 20,1992 04:48:1.514 34.9710 -116.9390 4.5900 4.57
Jul 20,1992 13:13:19.420 34.9920 -116.9480 0.0100 4.60
Jul 21 ,1992 21:10:29.029 34.2190 -116.7710 1.8600 4.05
Jul 24,1992 18:14:36.251 33.9010 -116.2840 8.2500 4.91
Jul 25,1992 04:31 :59.930 33.9370 -116.3050 4.6900 4.79
Aug 5,1992 15:41 :54.368 34.6460 -116.5290 4.2200 4.08
Aug 5,1992 22:22:40.825 34.9790 -116.9520 0.0100 4.68
Aug 6,1992 16:50:59.978 35.0260 -116.9670 4.7900 4.13
Aug 7,1992 00:43:28.392 34.2680 -116.7740 1.7300 4.10
Aug 8,1992 15:37:43.336 34.3770 -116.4580 2.8400 4.40
Aug 11,1992 06:11:17.246 34.0610 -116.3740 0.7500 4.27
Aug 15,1992 08:24: 14.660 34.0870 -116.4020 0.5100 4.77
Aug 17,1992 20:41:52.124 34.1950 -116.8620 11 .2700 5.16
Aug 18,1992 09:46:40.699 34.1980 -116.8620 12.8200 4.18
Table 4. Time shifts that were applied to the data in order to correct for known timing discrepencies.
Station Shift applied (secs) Comments
BNJI +4,+3 Initial leap second setting of 0 required +4 second shift before 183:00, and +3 second shift until correct leap second was set at 184:00.110.
BRCC no shifts applied No corrections necessary.
BRDO -2 CPU vsn 2.44 requires -2 second shift to all data.
CGTS -2 CPU vsn 2.44 requires -2 second shift to all data.
EDC2 -2 CPU vsn 2.44 requires -2 second shift to all data.
EORD -1 Leap second setting of 16 required -1 second shift for data from 183:00 - 183:19.
ERWL +4 Leap second setting of 0 required +4 second shift for all data.
FIRE -1, -2 Leap second corrections of -2 seconds for data before 185:19, and -1 second after 185:19.
FIR2 no shifts applied Due to clock failure, data timing is accurate to +/-0.5 seconds.
FORF +4 Leap second setting of 0 required +4 second shift for all data.
FRED no shifts applied Due to clock failure, data timing is accurate to +/-0.5 seconds.
GOLF no shifts applied Due to clock failure, data timing is accurate to +/-0.5 seconds.
GPOE -1 Leap second setting of 16 required -1 second shift from 183:00 - 189:18.
GRAC +4,+3 Initial leap second setting of 0 required +4 second shift before 183:00, and +3 second shift until correct leap second was set on 183:20.
GRAV +4 Leap second setting of 0 required +4 second shift for all data.
HILL -1, -2 Leap second corrections of -2 seconds for data before 185:22, and -1 second after 185:22.
IRON no shifts applied No corrections necessary.
JEAN no shifts applied Due to clock failure, data timing is accurate to +/-0.5 seconds.
JEFF no shifts applied Due to clock failure, data timing is accurate to +/-0.5 seconds.
JFRG no shifts applied Due to clock failure, data timing is accurate to +/-0.5 seconds.
LADY -1 Leap second correction of -1 second required for all data.
LPMA -1 Leap second setting of 16 required -1 second shift from 183:00 - 184:00.
RIMR -1, -2 Leap second corrections of -2 seconds for data before 199:05, and -1 second after 199:05.
ROKE no shifts applied Due to clock failure, data timing is accurate to +/-0.5 seconds.
ROKN no shifts applied Due to clock failure, data timing is accurate to +/-0.5 seconds.
ROKN no shifts applied Due to clock failure, data timing is accurate to +/-0.5 seconds.
UCVF n/a The DASs internal Omega card was faulty, resulting in inaccurately timed data.
UGGP no shifts applied Several periods of Omega lock/unlock during days 194 - 198 resulted in ~4 second data time drifts. No corrections were applied.
VVST -1 Leap second setting of 16 required -1 second shift from 183:00 - 184:00.
YKNF +4,+3 Initial leap second setting of 0 required +4 second shift before 183:00, and +3 second shift until correct leap second was set on 184:10.

Station Map

Station map

Station List

(table version)

sta   ondate   offdate   lat   lon   elev   staname   statype   refsta   dnorth   deast   
BNJI   1992181   1992207   34.1625   -116.321   0.827   Benji Road, Yucca Valley, Calif.   ss   -   0   0   
BRCC   1992182   1992246   34.0721   -116.3915   1.207   Black Rock Campground, Joshua Tree National Monume   ss   -   0   0   
BRDO   1992184   1992190   33.8296   -116.149   0.483   Berdoo Canyon, Joshua Tree National Monument, Cali   ss   -   0   0   
CGTS   1992190   1992224   34.9514   -116.8639   0.694   Callico Ghost Town, Barstow, Calif.   ss   -   0   0   
EDC2   1992182   1992206   33.9166   -116.3266   0.48   East Deception Canyon 2, Joshua Tree National Monu   ss   -   0   0   
EORD   1992182   1992246   34.6561   -116.718   1.16   East Ord Mountain, San Bernadino Co., Calif.   ss   -   0   0   
ERWL   1992181   1992200   34.2349   -116.7984   2.102   (Big Bear)   ss   -   0   0   
FIRE   1992181   1992189   34.0486   -116.578   0.749   Fire Station, Morongo Valley, Calif.   ss   -   0   0   
FORF   1992181   1992200   34.0883   -116.9205   1.596   Forrest Falls, San Bernadino Co., Calif.   ss   -   0   0   
GPOE   1992182   1992206   34.4227   -116.7169   0.894   George Poe's Place, San Bernadino Co., Calif.   ss   -   0   0   
GRAC   1992181   1992206   34.2668   -116.3882   0.913   Green Acres, Landers, Calif.   ss   -   0   0   
GRAV   1992181   1992200   34.187   -116.7198   2.454   (Big Bear)   ss   -   0   0   
HILL   1992181   1992220   34.3614   -116.4541   0.891   Hill, San Bernadino Co., Calif.   ss   -   0   0   
IRON   1992185   1992246   34.6167   -116.5671   1.152   Iron Ridge, San Bernadino Co., Calif.   ss   -   0   0   
JFRG   1992185   1992246   34.0457   -116.6215   0.862   Jumping Frog Lane, Morongo Valley, Calif.   ss   -   0   0   
LADY   1992189   1992220   34.1306   -116.3139   0.811   Lady's Place, Yucca Valley, Calif.   ss   -   0   0   
LPMA   1992182   1992206   34.3603   -116.4192   0.733   Los Padres Mine Access, San Bernadino Co., Calif.   ss   -   0   0   
RIMR   1992181   1992220   34.1865   -116.4634   1.099   Rimrock, San Bernadino Co., Calif.   ss   -   0   0   
UCVF   1992182   1992207   34.0108   -116.306   1.441   Upper Covington Flats, Joshua Tree National Monume   ss   -   0   0   
UGGP   1992185   1992246   34.7499   -116.6606   0.857   Under Ground Gas Pipeline Road, San Bernadino Co.,   ss   -   0   0   
VIPC   1992184   1992246   34.0177   -116.1903   1.246   Very Important Person Campground, Joshua Tree Nati   ss   -   0   0   
VVST   1992181   1992206   34.3596   -116.5789   0.912   Valley Vista Road, San Bernadino Co., Calif.   ss   -   0   0   
YKNF   1992181   1992206   34.2075   -116.4457   1.094   Yellowknife Road, San Bernadino Co., Calif.   ss   -   0   0   

Total: 23

Channel List

(table version)

sta   chan   ondate   chanid   offdate   ctype   edepth   hang   vang   descrip   
BNJI   EHE   1992181   1   1992207   n   -0   90   90   -   
BNJI   EHN   1992181   2   1992207   n   -0   0   90   -   
BNJI   EHZ   1992181   3   1992207   n   -0   0   180   -   
BNJI   ELE   1992181   4   1992207   n   -0   90   90   -   
BNJI   ELN   1992181   5   1992207   n   -0   0   90   -   
BNJI   ELZ   1992181   6   1992207   n   -0   0   0   -   
BRCC   HHE   1992182   7   1992246   n   -0   99   90   -   
BRCC   HHN   1992182   8   1992246   n   -0   9   90   -   
BRCC   HHZ   1992182   9   1992246   n   -0   0   0   -   
BRCC   HLE   1992182   10   1992246   n   -0   99   90   -   
BRCC   HLN   1992182   11   1992246   n   -0   9   90   -   
BRCC   HLZ   1992182   12   1992246   n   -0   0   0   -   
BRDO   ELE   1992184   13   1992190   n   -0   90   90   -   
BRDO   ELN   1992184   14   1992190   n   -0   0   90   -   
BRDO   ELZ   1992184   15   1992190   n   -0   0   0   -   
BRDO   HHE   1992184   16   1992190   n   -0   90   90   -   
BRDO   HHN   1992184   17   1992190   n   -0   0   90   -   
BRDO   HHZ   1992184   18   1992190   n   -0   0   0   -   
CGTS   ELE   1992190   19   1992224   n   -0   90   90   -   
CGTS   ELN   1992190   20   1992224   n   -0   0   90   -   
CGTS   ELZ   1992190   21   1992224   n   -0   0   0   -   
CGTS   HHE   1992190   22   1992224   n   -0   90   90   -   
CGTS   HHN   1992190   23   1992224   n   -0   0   90   -   
CGTS   HHZ   1992190   24   1992224   n   -0   0   0   -   
EDC2   ELE   1992182   25   1992206   n   -0   90   90   -   
EDC2   ELN   1992182   26   1992206   n   -0   0   90   -   
EDC2   ELZ   1992182   27   1992206   n   -0   0   0   -   
EDC2   HHE   1992182   28   1992206   n   -0   90   90   -   
EDC2   HHN   1992182   29   1992206   n   -0   0   90   -   
EDC2   HHZ   1992182   30   1992206   n   -0   0   0   -   
EORD   EHE   1992182   31   1992246   n   -0   86   90   -   
EORD   EHN   1992182   32   1992246   n   -0   356   90   -   
EORD   EHZ   1992182   33   1992246   n   -0   0   180   -   
EORD   ELE   1992182   34   1992246   n   -0   89   90   -   
EORD   ELN   1992182   35   1992246   n   -0   359   90   -   
EORD   ELZ   1992182   36   1992246   n   -0   0   0   -   
ERWL   EHE   1992181   37   1992200   n   -0   90   90   -   
ERWL   EHN   1992181   38   1992200   n   -0   0   90   -   
ERWL   EHZ   1992181   39   1992200   n   -0   0   180   -   
ERWL   ELE   1992181   40   1992200   n   -0   90   90   -   
ERWL   ELN   1992181   41   1992200   n   -0   0   90   -   
ERWL   ELZ   1992181   42   1992200   n   -0   0   0   -   
FIRE   EHE   1992181   43   1992189   n   -0   90   90   -   
FIRE   EHN   1992181   44   1992189   n   -0   0   90   -   
FIRE   EHZ   1992181   45   1992189   n   -0   0   0   -   
FIRE   ELE   1992181   46   1992189   n   -0   90   90   -   
FIRE   ELN   1992181   47   1992189   n   -0   0   90   -   
FIRE   ELZ   1992181   48   1992189   n   -0   0   0   -   
FORF   EHE   1992181   49   1992200   n   -0   90   90   -   
FORF   EHN   1992181   50   1992200   n   -0   0   90   -   
FORF   EHZ   1992181   51   1992200   n   -0   0   0   -   
FORF   ELE   1992181   52   1992200   n   -0   90   90   -   
FORF   ELN   1992181   53   1992200   n   -0   0   90   -   
FORF   ELZ   1992181   54   1992200   n   -0   0   0   -   
GPOE   EHE   1992182   55   1992206   n   -0   90   90   -   
GPOE   EHN   1992182   56   1992206   n   -0   0   90   -   
GPOE   EHZ   1992182   57   1992206   n   -0   0   180   -   
GPOE   ELE   1992182   58   1992206   n   -0   90   90   -   
GPOE   ELN   1992182   59   1992206   n   -0   0   90   -   
GPOE   ELZ   1992182   60   1992206   n   -0   0   0   -   
GRAC   EHE   1992181   61   1992206   n   -0   87   90   -   
GRAC   EHN   1992181   62   1992206   n   -0   357   90   -   
GRAC   EHZ   1992181   63   1992206   n   -0   0   0   -   
GRAC   ELE   1992181   64   1992206   n   -0   90   90   -   
GRAC   ELN   1992181   65   1992206   n   -0   0   90   -   
GRAC   ELZ   1992181   66   1992206   n   -0   0   0   -   
GRAV   EHE   1992181   67   1992200   n   -0   90   90   -   
GRAV   EHN   1992181   68   1992200   n   -0   0   90   -   
GRAV   EHZ   1992181   69   1992200   n   -0   0   0   -   
GRAV   ELE   1992181   70   1992200   n   -0   90   90   -   
GRAV   ELN   1992181   71   1992200   n   -0   0   90   -   
GRAV   ELZ   1992181   72   1992200   n   -0   0   0   -   
HILL   EHE   1992181   73   1992220   n   -0   90   90   -   
HILL   EHN   1992181   74   1992220   n   -0   0   90   -   
HILL   EHZ   1992181   75   1992220   n   -0   0   0   -   
HILL   ELE   1992181   76   1992220   n   -0   90   90   -   
HILL   ELN   1992181   77   1992220   n   -0   0   90   -   
HILL   ELZ   1992181   78   1992220   n   -0   0   0   -   
IRON   EHE   1992185   79   1992246   n   -0   99   90   -   
IRON   EHN   1992185   80   1992246   n   -0   9   90   -   
IRON   EHZ   1992185   81   1992246   n   -0   0   0   -   
IRON   ELE   1992185   82   1992246   n   -0   90   90   -   
IRON   ELN   1992185   83   1992246   n   -0   0   90   -   
IRON   ELZ   1992185   84   1992246   n   -0   0   0   -   
JFRG   HHE   1992185   85   1992246   n   -0   82   90   -   
JFRG   HHN   1992185   86   1992246   n   -0   352   90   -   
JFRG   HHZ   1992185   87   1992246   n   -0   0   0   -   
JFRG   HLE   1992185   88   1992246   n   -0   82   90   -   
JFRG   HLN   1992185   89   1992246   n   -0   352   90   -   
JFRG   HLZ   1992185   90   1992246   n   -0   0   0   -   
LADY   EHE   1992189   91   1992220   n   -0   90   90   -   
LADY   EHN   1992189   92   1992220   n   -0   0   90   -   
LADY   EHZ   1992189   93   1992220   n   -0   0   0   -   
LADY   ELE   1992189   94   1992220   n   -0   90   90   -   
LADY   ELN   1992189   95   1992220   n   -0   0   90   -   
LADY   ELZ   1992189   96   1992220   n   -0   0   0   -   
LPMA   EHE   1992182   97   1992206   n   -0   100   90   -   
LPMA   EHN   1992182   98   1992206   n   -0   10   90   -   
LPMA   EHZ   1992182   99   1992206   n   -0   0   180   -   
LPMA   ELE   1992182   100   1992206   n   -0   100   90   -   
LPMA   ELN   1992182   101   1992206   n   -0   10   90   -   
LPMA   ELZ   1992182   102   1992206   n   -0   0   0   -   
RIMR   EHE   1992181   103   1992220   n   -0   90   90   -   
RIMR   EHN   1992181   104   1992220   n   -0   0   90   -   
RIMR   EHZ   1992181   105   1992220   n   -0   0   0   -   
RIMR   ELE   1992181   106   1992220   n   -0   90   90   -   
RIMR   ELN   1992181   107   1992220   n   -0   0   90   -   
RIMR   ELZ   1992181   108   1992220   n   -0   0   0   -   
UCVF   EHE   1992182   109   1992207   n   -0   85   90   -   
UCVF   EHN   1992182   110   1992207   n   -0   355   90   -   
UCVF   EHZ   1992182   111   1992207   n   -0   0   180   -   
UGGP   EHE   1992185   112   1992246   n   -0   267   90   -   
UGGP   EHN   1992185   113   1992246   n   -0   177   90   -   
UGGP   EHZ   1992185   114   1992246   n   -0   0   180   -   
UGGP   ELE   1992185   115   1992246   n   -0   90   90   -   
UGGP   ELN   1992185   116   1992246   n   -0   0   90   -   
UGGP   ELZ   1992185   117   1992246   n   -0   0   0   -   
VIPC   HHE   1992184   118   1992246   n   -0   94   90   -   
VIPC   HHN   1992184   119   1992246   n   -0   4   90   -   
VIPC   HHZ   1992184   120   1992246   n   -0   0   0   -   
VIPC   HLE   1992184   121   1992246   n   -0   94   90   -   
VIPC   HLN   1992184   122   1992246   n   -0   4   90   -   
VIPC   HLZ   1992184   123   1992246   n   -0   0   0   -   
VVST   EHE   1992181   124   1992206   n   -0   94   90   -   
VVST   EHN   1992181   125   1992206   n   -0   4   90   -   
VVST   EHZ   1992181   126   1992206   n   -0   0   180   -   
VVST   ELE   1992181   127   1992206   n   -0   90   90   -   
VVST   ELN   1992181   128   1992206   n   -0   0   90   -   
VVST   ELZ   1992181   129   1992206   n   -0   0   0   -   
YKNF   EHE   1992181   130   1992206   n   -0   90   90   -   
YKNF   EHN   1992181   131   1992206   n   -0   0   90   -   
YKNF   EHZ   1992181   132   1992206   n   -0   0   180   -   
YKNF   ELE   1992181   133   1992206   n   -0   90   90   -   
YKNF   ELN   1992181   134   1992206   n   -0   0   90   -   
YKNF   ELZ   1992181   135   1992206   n   -0   0   0   -   

Total: 135

URL: http://eqinfo.ucsd.edu/deployments/portable_aftershock_studies/landers_big_bear.php [Last updated: 2015-10-22 (295) 22:24:32 UTC]