SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey November 6, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ October 30 - November 5, 1997 Prepared by: Kate Hutton, 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. -------------------------------- ***************************************************************** If you receive this Report by FAX and if you have recently had a change of AREA CODE, please notify us ASAP. We have no other way to know which fax numbers need to be changed!! Actually, if your area code is 818 and it HASN'T changed, it would be helpful to know that, too. ***************************************************************** This week's Report covers the time period from midnight Thursday morning, October 30, Universal Time (ie. UTC), to midnight Wednesday night, November 5, Universal Time. In local time, the period of coverage is from 4 p.m., October 29, Pacific Standard Time, to 4 p.m., November 5, Pacific Standard Time. We detected 229 earthquakes during the seven-day period covered. These Weekly Reports should not be used for archival purposes. Further data processing often changes the magnitudes slightly and, especially during times of high seismicity, sometimes changes the estimates of total seismicity. For the best earthquake catalog currently available, see: http://scec.gps.caltech.edu/catalog-search.html The largest quake this week, and the only one that was felt, occurred early Tuesday morning in Fontana. It had a magnitude of M3.6 and a strike-slip focal mechanism. This quake is part of a northeast-southwest trend of seismic activity known as the 'Fontana trend'. No large earthquakes or mapped faults have ever been attributable to that trend, but quakes in the M3 range have been relatively common. All the earthquakes in this lineation show strike-slip faulting. The trend is probably a northeast-striking left-lateral fault that is buried under the sediments of the San Bernardino Valley (and therefore unmappable). Similar left-lateral faults include the San Jose Fault, responsible for the Upland earthquake (M5.2 in 1990) and the Raymond Fault in San Marino. This week's quake was felt fairly widely in the Inland Empire. The only other M3+ quake this week occurred offshore, near San Clemente Is. (on Tuesday afternoon), and was not felt. 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 ------------------------------------------------------------- 10/30 6:25 am 36 1.6 117 46.2 2.0 10 mi. E of Coso Junction 10/30 3:09 pm 36 8.4 119 35.6 2.8 21 mi. SW of Visalia 10/30 3:36 pm 35 44.1 117 38.0 2.8 7 mi. NNE of Ridgecrest 10/30 3:38 pm 35 44.1 117 38.0 2.2 " 10/30 11:41 pm 34 0.1 116 47.1 2.0 5 mi. N of Cabazon 10/31 1:08 am 34 50.9 117 26.7 2.3 15 mi. SE of Boron 10/31 6:45 am 34 59.0 116 56.4 2.1 8 mi. NE of Barstow 10/31 10:16 pm 33 10.6 116 2.5 2.4 5 mi. ENE of Ocotillo Wells 11/1 11:58 am 32 2.8 115 42.5 2.5 44 mi. SSW of Calexico 11/1 7:57 pm 35 5.3 117 29.4 2.5 10 mi. NE of Boron 11/2 3:34 am 33 27.9 116 26.0 2.3 14 mi. NNW of Borrego Springs 11/2 5:44 pm 34 9.2 116 25.5 2.5 2 mi. NNE of Yucca Valley 11/2 8:29 pm 33 52.1 117 50.2 2.2 1 mi. SW of Yorba Linda 11/3 4:37 am 34 25.1 116 28.7 2.0 20 mi. N of Yucca Valley 11/3 10:46 am 34 56.4 116 55.5 2.3 6 mi. ENE of Barstow 11/3 6:08 pm 36 4.8 117 39.0 2.2 16 mi. E of Coso Junction 11/3 8:24 pm 34 22.7 116 28.2 2.0 18 mi. N of Yucca Valley 11/4 2:36 am 34 16.4 117 2.0 2.3 6 mi. NE of Running Springs 11/4 6:36 am 34 6.3 117 25.8 3.6 Under Fontana; FELT 11/4 2:37 pm 32 9.0 115 48.3 2.5 40 mi. SSW of Calexico 11/4 2:43 pm 32 40.5 118 2.8 3.0 20 mi. ESE of San Clemente Is. (SE tip) 11/4 4:55 pm 35 46.9 117 39.2 2.6 11 mi. N of Ridgecrest 11/4 7:48 pm 33 51.4 117 2.0 2.0 5 mi. SSW of Beaumont 11/5 2:37 am 33 54.0 118 18.3 2.2 2 mi. ESE of Hawthorne 11/5 6:54 am 36 5.9 117 39.7 2.5 16 mi. ENE of Coso Junction 11/5 9:28 am 34 19.5 116 46.0 2.1 6 mi. NE of Big Bear City 11/5 10:30 am 32 7.4 115 51.4 2.5 42 mi. S of Ocotillo -------------------------------------------------------------