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

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

Total: 23

Channel List

(plain text 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]