SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey February 12, 1998 Weekly Earthquake Report for Southern California ------------------------------------------------ February 5 - 11, 1998 Prepared by: Nick Scheckel, Seismological Laboratory (kate@bombay.gps.caltech.edu) Lucy Jones, U. S. Geological Survey California Institute of Technology For further information, please contact the authors, or the Caltech Public Relations Office at 626-395-6327. For daily updates, call our Earthquake Information Hotline: 626-395-6977. -------------------------------- ****************************************************************** As many of you know by now, the U.S. Geological Survey in Menlo Park, the office which originates the Northern California Earthquake Report, is planning to discontinue the paper (and faxed) Report at the end of February 1998. We plan to follow their initiative. As of the beginning of March 1998, we will be replacing our weekly 'treeware' product with a Web site, which will include the same map, table, and commentary as the current Weekly Report, plus other features. The Web page will be updated more often than once per week. You will be able to get to this web site form the following home pages: http://www.gps.caltech.edu/seismo/ http://www-socal.wr.usgs.gov/ http://www.scecdc.scec.org/ http://www.trinet.org/ (The last one does not exist yet, but will soon.) There will be no paper copy or usenet distribution. We hope we are giving our Users sufficient notice to obtain World Wide Web access for themselves. At minimum, most public libraries now provide Web access, along with the capability to print copies of Web pages. ****************************************************************** This week's Report covers the time period from midnight Thursday morning, February 5, Universal Time (ie. UTC), to midnight Wednesday night, February 11, Universal Time. In local time, the period of coverage is from 4 p.m., February 4, Pacific Standard Time, to 4 p.m., February 11, Pacific Standard Time. We detected 187 earthquakes during the seven-day period covered. Note that we have decided to extend the production of the Weekly Report through February, or until we have thoroughly tested some of our newest software. This has been another quiet week, seismically speaking. There were only two earthquakes above M3.0 and neither were reported as being felt. It is likely however the M3.1 near Hemet, which occurred early Saturday morning might have woken someone up. Although this earthquake is located within the San Jacinto Fault Zone (a broad area with many fault strands) where the primary motion is strike-slip, the focal mechanism showed thrust faulting. We therefore assume that the event proably occurred on a small, secondary fault in the system that perhaps accomodates a step between larger strands. Offshore Huntington beach a M3.2 occurred Tuesday evening. It is possible this too might have been felt although it wasn't reported as such. This earthquake also resulted from thrust faulting. This is a common mechanism in this area of uplift around the Palos Verdes fault. Table 1 lists the quakes this week that were M2.0 or larger in the central part of the coverage area. Times are local times; if you want Greenwich Mean Time, add 7 hrs to the Pacific Daylight Time or 8 hrs to the Pacific Standard Time listed. Table 1 ------- Date Time N Lat. W Long. Mag ------------------------------------------------------------- 2/ 5 1:06 am 32 51.5 115 39.6 2.6 7 mi. NW of El Centro 2/ 5 1:57 am 33 2.0 116 24.8 2.2 11 mi. ESE of Julian 2/ 5 5:22 am 34 58.6 120 44.7 2.3 6 mi. NW of Pt. Sal 2/ 5 5:23 am 33 12.9 116 11.3 2.5 5 mi. NW of Ocotillo Wells 2/ 5 9:29 am 36 7.6 117 40.8 2.0 15 mi. ENE of Coso Junction 2/ 5 1:07 pm 34 58.5 116 48.7 2.0 13 mi. ENE of Barstow 2/ 5 1:50 pm 34 24.2 116 27.4 2.4 19 mi. N of Yucca Valley 2/ 5 6:07 pm 34 23.2 118 42.2 2.0 7 mi. N of Simi Valley 2/ 5 9:23 pm 32 6.6 116 26.7 2.5 46 mi. SE of San Ysidro 2/ 6 4:27 pm 34 10.7 116 26.5 2.3 4 mi. N of Yucca Valley 2/ 7 1:34 am 33 47.4 116 58.5 3.1 3 mi. N of Hemet 2/ 7 9:25 am 33 59.6 117 0.4 2.3 3 mi. SSE of Yucaipa 2/ 7 9:40 am 34 20.1 116 54.6 2.0 5 mi. NW of Big Bear City 2/ 7 10:53 am 32 26.1 115 6.1 2.5 28 mi. SE of Calexico 2/ 8 8:00 am 34 57.2 116 47.0 2.9 14 mi. ENE of Barstow 2/ 8 12:18 pm 35 59.8 117 22.5 2.1 15 mi. N of Trona 2/ 9 7:31 pm 32 31.4 116 17.6 2.1 22 mi. SW of Ocotillo 2/10 12:58 am 34 21.1 116 27.9 2.2 16 mi. N of Yucca Valley 2/10 3:53 am 32 20.3 116 18.8 2.0 33 mi. SW of Ocotillo 2/10 7:01 pm 36 14.1 120 13.1 2.7 10 mi. NE of Coalinga 2/10 7:39 pm 33 46.9 116 56.9 2.4 2 mi. NNE of Hemet 2/10 8:49 pm 33 33.2 118 9.3 3.2 11 mi. SW of Bolsa Chica Beach 2/10 11:56 pm 33 32.5 118 8.3 2.2 11 mi. SSW of Bolsa Chica Beach -------------------------------------------------------------