SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey October 2, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ September 25 - October 1, 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, September 25, Universal Time (ie. UTC), to midnight Wednesday night, October 1, Universal Time. In local time, the period of coverage is from 5 p.m., September 24, Pacific Daylight Time, to 5 p.m., October 1, Pacific Daylight Time. We detected 217 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 biggest excitement for this week was a M4.4 Landers aftershock early Sunday morning. It was felt pretty widely in the Yucca Valley and Palm Springs area. Like all Landers aftershocks in this area, it had a strike-slip focal mechanism. The last time we had an aftershock this big on this part of the rupture was in September of 1995; it was also M4.4. The other quake that was felt this week occurred early last Thursday afternoon. It was a M3.4 in the San Gabriel Mtns. north of Lake View Terrace. It was felt in the northeastern San Fernando Valley. The focal mechanism was west-northwest striking thrust. Incidently, this quake was in the eastern part of the old San Fernando (1971 - remember?) aftershock zone, although the elapsed time is such that we don't care to call it an aftershock. Speaking of 'oldies, but goodies', did anyone notice that yesterday was the 10th anniversary of the Whittier Narrows quake? 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 ------------------------------------------------------------- 9/25 1:08 pm 34 24.0 118 21.0 3.4 8 mi. N of Lake View Terrace; FELT 9/25 2:51 pm 35 47.4 117 39.2 2.1 11 mi. N of Ridgecrest 9/26 3:34 am 32 14.8 115 18.2 2.6 31 mi. SSE of Calexico 9/26 9:40 am 32 32.1 115 38.3 2.8 12 mi. SW of Calexico 9/26 5:24 pm 33 8.1 117 49.2 2.2 23 mi. SSW of Dana Point 9/27 12:28 am 36 3.4 119 36.1 2.4 25 mi. SW of Visalia 9/27 12:08 pm 34 9.9 117 19.8 2.6 4 mi. NNW of San Bernardino 9/27 11:13 pm 36 5.7 117 39.2 2.5 16 mi. ENE of Coso Junction 9/28 5:08 am 34 14.4 119 29.5 2.0 10 mi. S of Carpinteria 9/28 8:57 am 34 18.1 116 27.1 4.4 12 mi. N of Yucca Valley WIDELY FELT 9/28 9:19 am 36 17.3 118 19.5 2.3 20 mi. S of Mt. Whitney 9/28 9:32 am 34 18.2 116 27.2 2.7 12 mi. N of Yucca Valley 9/28 10:34 pm 34 18.3 116 26.7 2.0 " 9/29 12:43 am 36 0.5 117 23.8 2.2 16 mi. N of Trona 9/29 4:06 am 36 0.5 117 24.4 2.4 " 9/29 9:52 pm 33 48.2 118 12.8 2.0 2 mi. NW of Long Beach 9/29 10:48 pm 33 57.4 116 19.5 2.6 10 mi. E of Desert Hot Springs 9/30 1:49 pm 34 18.3 116 27.1 2.3 12 mi. N of Yucca Valley 9/30 3:28 pm 34 37.8 116 32.0 2.6 26 mi. ENE of Lucerne Valley 9/30 3:31 pm 34 38.3 116 32.1 2.0 " 9/30 7:34 pm 32 15.7 115 43.6 2.5 31 mi. SSW of Calexico 9/30 8:27 pm 33 29.8 118 14.7 2.7 11 mi. NNE of Avalon, Catalina Island 10/1 12:09 am 34 19.8 116 28.2 2.1 14 mi. N of Yucca Valley 10/1 2:23 am 34 18.4 116 26.8 2.0 12 mi. N of Yucca Valley 10/1 7:44 am 34 20.2 116 27.7 2.6 15 mi. N of Yucca Valley -------------------------------------------------------------