SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey August 21, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ August 14 - 20, 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 818-395-6327. For daily updates, call our Earthquake Information Hotline: 818-395-6977. -------------------------------- ***************************************************************** 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!! ***************************************************************** This week's Report covers the time period from midnight Thursday morning, August 14, Universal Time (ie. UTC), to midnight Wednesday night, August 20, Universal Time. In local time, the period of coverage is from 5 p.m., August 13, Pacific Daylight Time, to 5 p.m., August 20, Pacific Daylight Time. We detected 307 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 activity south of the U.S./Mexico border continued this week, which accounts for the relatively large total number of events. It is interesting that the Baja activity is going on at two distinct locations, on different faults. The activity within our actual coverage area was rather quiet. The two largest events were both M2.8's: one a North- ridge aftershock on Sunday afternoon, and the other near Baldwin Park on Tuesday afternoon. Both events had mostly stike-slip focal mechanisms. Surprisingly, we got no inquiries on either of these events. The Northridge quake took place in the mountains north of the main population center, which may account for it being unnoticed. As for the Baldwin Park quake, who knows? Meanwhile, a couple of very small Northridge aftershocks were felt. The first was a M2.4 near Northridge on Sunday morning, and the second was a M2.2 near Granada Hills on Tuesday evening. The Northern California Report should be consulted for more information on the Coalinga area quakes. 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 ------------------------------------------------------------- 8/13 5:01 pm 35 47.5 117 39.5 2.4 11 mi. N of Ridgecrest 8/13 5:28 pm 34 6.6 116 56.0 2.1 6 mi. W of Mt. San Gorgonio 8/13 8:52 pm 32 15.0 115 8.3 2.5 35 mi. SE of Calexico 8/14 2:11 am 33 21.2 116 26.6 2.0 7 mi. NNW of Borrego Springs 8/14 6:24 am 33 0.3 116 21.6 2.1 17 mi. S of Borrego Springs 8/14 7:37 am 34 8.9 117 19.9 2.0 3 mi. NW of San Bernardino 8/14 8:18 am 32 51.1 118 23.1 2.3 3 mi. NW of San Clemente Is. (SE tip) 8/14 8:29 am 32 18.9 115 6.1 2.5 33 mi. SE of Calexico 8/14 11:55 am 33 4.9 116 3.7 2.6 5 mi. SE of Ocotillo Wells 8/14 1:40 pm 34 24.9 116 33.2 2.1 21 mi. NNW of Yucca Valley 8/14 2:33 pm 32 6.9 115 45.9 2.6 41 mi. SSW of Calexico 8/14 10:51 pm 34 20.7 116 27.6 2.5 15 mi. N of Yucca Valley 8/14 10:58 pm 34 20.7 116 27.7 2.4 " 8/15 1:14 am 34 26.3 119 18.1 2.1 3 mi. WSW of Ojai 8/15 8:07 am 33 15.6 116 0.2 2.1 2 mi. WSW of Salton City 8/15 11:03 am 35 45.1 117 39.3 2.0 9 mi. N of Ridgecrest 8/15 4:22 pm 32 21.1 115 5.9 2.5 31 mi. SE of Calexico 8/15 6:14 pm 32 9.0 115 47.1 3.0 39 mi. SSW of Calexico 8/15 7:08 pm 34 16.4 118 26.5 2.3 Under Pacoima 8/15 7:52 pm 36 23.7 120 16.6 2.8 18 mi. NNE of Coalinga 8/15 10:56 pm 32 19.9 115 16.3 2.6 26 mi. SSE of Calexico 8/16 1:22 pm 32 40.0 115 54.5 2.3 6 mi. SE of Ocotillo 8/16 1:26 pm 32 39.9 115 54.3 2.1 " 8/17 3:11 am 34 26.6 116 28.5 2.2 22 mi. N of Yucca Valley 8/17 6:54 am 36 4.7 117 50.8 2.1 6 mi. ENE of Coso Junction 8/17 9:18 am 34 16.4 118 33.5 2.4 3 mi. NNW of Northridge FELT 8/17 9:19 am 34 16.4 118 33.3 2.0 " 8/17 1:20 pm 34 19.4 118 27.6 2.8 2 mi. NNW of San Fernando 8/18 12:42 am 35 16.5 118 32.8 2.1 11 mi. NNW of Tehachapi 8/18 12:44 am 35 21.5 116 32.9 2.2 19 mi. E of Goldstone Lake 8/18 8:13 am 33 16.1 116 0.6 2.4 2 mi. WSW of Salton City 8/18 3:18 pm 34 7.0 116 59.3 2.5 6 mi. NNE of Yucaipa 8/19 2:39 am 32 13.1 115 48.7 2.7 37 mi. SSE of Ocotillo 8/19 10:05 am 34 8.9 117 20.0 2.4 3 mi. NE of Rialto 8/19 2:37 pm 34 6.4 117 57.5 2.8 1 mi. N of Baldwin Park 8/19 3:25 pm 35 16.5 118 32.8 2.2 11 mi. NNW of Tehachapi 8/19 6:54 pm 34 15.9 118 28.4 2.2 1 mi. ESE of Granada Hills; FELT 8/19 9:12 pm 34 54.9 116 48.1 2.0 12 mi. E of Barstow 8/20 6:08 am 34 12.3 117 35.3 2.2 6 mi. N of Rancho Cucamonga 8/20 11:47 am 33 29.8 115 28.0 2.2 15 mi. SSW of Desert Center 8/20 1:25 pm 32 43.2 115 57.2 2.1 2 mi. ESE of Ocotillo -------------------------------------------------------------