SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey August 22, 1996 Weekly Earthquake Report for Southern California ------------------------------------------------ August 15 - 21, 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 15, Universal Time (ie. GMT), to midnight Wednesday night, August 21, Universal Time. In local time, the period of coverage is from 5 p.m., August 14, Pacific Daylight Time, to 5 p.m., August 21, Pacific Daylight Time. We detected and processed 250 earthquakes during the seven-day period covered. There were two "largest quakes" this week, both M3.3. The first one occurred in the San Gorgonio Pass area early last Thursday morning, in an area which is a common source for small earthquakes. It's focal mechanism showed normal faulting on north-striking faults, at a depth of 18 km. This normal faulting at the bottom of the seismogenic zone is characteristic of this region. The second M3.3 occurred well offshore, on Monday morning. One other, smaller event was felt. That event was a M2.6 Northridge aftershock near Simi Valley very early Wednesday morning. Small quakes continued to occur near Obsidian Butte in the northern Imperial Valley and at the site of the M4.3 Landers aftershock last week. 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 ------------------------------------------------------------- 8/14 6:36 pm 33 10.7 115 36.0 2.6 2 mi. ENE of Obsidian Butte 8/14 7:36 pm 33 10.1 115 36.0 2.3 " 8/14 8:37 pm 34 35.8 116 16.3 2.0 31 mi. N of Joshua Tree 8/15 4:59 am 33 15.7 116 2.6 2.0 4 mi. WSW of Salton City 8/15 5:17 am 33 57.8 116 53.3 3.3 2 mi. NNW of Banning FELT 8/15 6:36 am 34 3.2 118 58.0 2.3 1 mi. WNW of Leo Carrillo State Beach 8/15 10:35 am 33 10.7 115 36.2 2.5 2 mi. ENE of Obsidian Butte 8/15 3:43 pm 34 36.0 116 16.9 2.4 32 mi. N of Joshua Tree 8/15 10:04 pm 33 42.4 116 49.6 2.4 7 mi. WSW of Idyllwild 8/16 6:27 am 34 35.8 116 16.4 2.7 32 mi. N of Joshua Tree 8/16 6:27 am 34 36.4 116 17.0 2.9 " 8/16 7:57 am 33 10.9 115 36.0 2.3 2 mi. ENE of Obsidian Butte 8/16 3:36 pm 34 36.1 116 17.5 2.0 32 mi. N of Joshua Tree 8/16 5:31 pm 34 35.8 116 17.6 2.1 " 8/16 5:48 pm 36 13.6 120 19.6 2.5 6 mi. NNE of Coalinga 8/17 4:20 am 33 15.6 116 2.3 2.1 4 mi. WSW of Salton City 8/17 6:58 am 34 2.0 116 19.0 2.6 7 mi. S of Joshua Tree 8/17 8:00 am 33 55.8 118 46.2 2.7 5 mi. SSE of Pt. Dume 8/17 3:17 pm 32 31.4 117 28.6 2.2 21 mi. SW of Mission Beach 8/17 3:29 pm 35 2.5 119 0.1 2.3 4 mi. NW of Wheeler Ridge 8/18 3:20 am 36 28.6 117 49.4 2.1 16 mi. NE of Olancha 8/18 4:34 pm 34 51.5 116 36.5 2.1 23 mi. E of Barstow 8/18 10:25 pm 34 14.4 119 41.6 2.1 12 mi. S of downtown Santa Barbara 8/19 6:57 am 33 15.9 116 17.1 2.2 5 mi. E of Borrego Springs 8/19 8:05 am 32 57.8 119 8.3 3.3 28 mi. SE of San Nicolas Is. 8/19 1:49 pm 34 2.8 117 11.6 2.1 1 mi. WSW of Redlands 8/19 6:24 pm 35 48.0 117 38.2 2.0 12 mi. N of Ridgecrest 8/20 3:44 am 36 13.8 120 48.0 2.8 25 mi. WNW of Coalinga 8/20 11:08 pm 34 56.9 116 46.7 2.2 14 mi. ENE of Barstow 8/21 2:18 am 34 14.8 118 41.0 2.6 2 mi. SSE of Simi Valley FELT 8/21 9:25 am 35 49.4 117 42.3 2.2 14 mi. N of Ridgecrest -------------------------------------------------------------