SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey August 8, 1996 Weekly Earthquake Report for Southern California ------------------------------------------------ August 1 - 7, 1996 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 818-395-6326. For daily updates, call our Earthquake Information Hotline: 818-395-6977. -------------------------------- This week's Report covers the time period from midnight Thursday morning, August 1, Universal Time (ie. GMT), to midnight Wednesday night, August 7, Universal Time. In local time, the period of coverage is from 5 p.m., July 31, Pacific Daylight Time, to 5 p.m., August 1, Pacific Daylight Time. We detected and processed 278 earthquakes during the seven-day period covered. There were three quakes felt this week. The first two, a M3.0 and a M2.7 very early Monday morning, were located in the Castaic Lake area, north of the Northridge aftershock zone. They had thrust focal mechanisms. The third felt quake was a M3.4 early Tuesday morning in the San Bernardino Mtns, located about a mile southeast of the Big Bear aftershock zone. It's focal mechanism showed right-lateral strike-slip faulting on a west- northwest-striking plane with a small oblique normal component. This quake was felt in the Banning area. None of these three are considered aftershocks. The small swarm at Obsidian Butte in the Imperial Valley continued this week, with 18 more small events. The largest was a M2.8 on Wednesday afternoon. All the rest were M2.1 or smaller. All in all, the week's seismicity was very ordinary. 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 ------------------------------------------------------------- 7/31 5:22 pm 36 33.8 117 50.1 2.2 12 mi. ESE of Lone Pine 8/1 1:36 am 33 59.3 117 10.9 2.4 4 mi. S of Redlands 8/1 3:08 am 33 11.4 115 34.1 2.1 4 mi. SW of Niland 8/1 8:57 am 34 26.5 116 30.0 2.1 22 mi. N of Yucca Valley 8/1 8:46 pm 35 43.7 117 37.3 2.0 7 mi. NNE of Ridgecrest 8/1 9:22 pm 35 10.3 119 6.3 2.0 15 mi. SSW of Bakersfield 8/2 2:08 am 34 55.9 116 55.3 2.0 6 mi. ENE of Barstow 8/2 7:11 am 33 54.0 120 10.4 2.5 4 mi. SW of Santa Rosa Is. 8/2 8:29 pm 36 4.5 117 59.8 2.0 3 mi. NW of Coso Junction 8/2 9:38 pm 34 56.2 116 45.6 2.3 15 mi. ENE of Barstow 8/3 1:09 pm 35 30.5 117 29.4 2.2 12 mi. SE of Ridgecrest 8/3 6:38 pm 34 28.2 116 31.0 2.3 24 mi. N of Yucca Valley 8/4 4:50 am 33 46.8 116 8.3 2.3 6 mi. NE of Indio 8/4 6:14 am 34 22.1 118 33.4 2.3 1 mi. S of Valencia 8/4 4:52 pm 36 16.5 120 21.7 2.7 9 mi. N of Coalinga 8/4 8:39 pm 33 49.2 119 17.6 2.1 19 mi. SE of Santa Cruz Is. (E end) 8/5 12:26 am 33 49.8 116 11.9 2.8 8 mi. N of Indio 8/5 2:33 am 32 1.3 114 58.5 3.1 50 mi. SSW of Yuma, Arizona 8/5 2:49 am 32 5.7 114 60.0 2.8 " 8/5 3:00 am 34 37.6 118 38.6 3.0 7 mi. N of Castaic Lake dam; FELT 8/5 3:03 am 34 37.5 118 38.5 2.7 " FELT 8/5 9:44 am 32 39.0 116 5.7 2.0 8 mi. SW of Ocotillo 8/5 10:52 am 32 0.4 115 46.7 2.6 48 mi. SSW of Calexico 8/5 6:57 pm 34 36.1 116 37.5 2.0 21 mi. ENE of Lucerne Valley 8/5 8:19 pm 34 36.9 116 39.6 2.0 " 8/6 12:18 am 36 12.3 118 16.0 2.2 15 mi. WSW of Olancha 8/6 3:44 am 34 58.7 116 50.2 2.1 12 mi. ENE of Barstow 8/6 4:52 am 34 4.7 116 46.9 3.4 2 mi. ESE of Mt. San Gorgonio; FELT 8/6 6:48 am 35 1.5 116 59.0 2.1 9 mi. NNE of Barstow 8/6 2:43 pm 36 9.1 118 4.3 2.0 7 mi. W of Haiwee Reser- voir (S end) 8/6 10:12 pm 32 29.0 115 34.0 2.0 13 mi. SSW of Calexico 8/6 11:59 pm 34 15.6 118 45.2 2.2 2 mi. WSW of Simi Valley 8/7 5:21 am 35 44.6 117 37.5 2.7 8 mi. NNE of Ridgecrest 8/7 5:23 am 35 44.5 117 37.4 2.0 " 8/7 6:45 am 35 44.6 117 37.4 2.0 " 8/7 3:21 pm 33 10.4 115 36.1 2.8 2 mi. E of Obsidian Butte 8/7 4:26 pm 33 10.5 115 35.8 2.1 " -------------------------------------------------------------