SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey September 12, 1996 Weekly Earthquake Report for Southern California ------------------------------------------------ September 5 - 11, 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, September 5, Universal Time (ie. GMT), to midnight Wednesday night, September 11, Universal Time. In local time, the period of coverage is from 5 p.m., September 4, Pacific Daylight Time, to 5 p.m., September 11, Pacific Daylight Time. We detected and processed 483 earthquakes during the seven-day period covered. In spite of the relatively large number of events this week, there were only three with magnitude M3 or larger. All three were members of small earthquake swarms that have inflated the week's total number of events. The first one, a M3.4 last Thursday morning, was part of the ongoing swarm in the Coso Range northeast of Ridgecrest. The second, on Sunday afternoon, was part of the small swarm in the Mojave Desert, near Boron. It had a magnitude of M3.1. There was also a M2.9 in this sequence. Both the Coso and Boron swarms were active last week. The last M3+, and the largest, took place late Tuesday afternoon at the Ridgecrest location, familiar from the large swarms in August and September of last year. This week's largest had a magnitude of M3.7. Like other Ridgecrest aftershocks, this event was a strike-slip event with right-lateral motion on a northwest- striking plane (or left-lateral on a northeast-striking plane). The other two earthquakes, at Mojave and Coso, both had a large normal component on north-striking planes. We received no public inquiries about any of these. 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 ------------------------------------------------------------- 9/4 7:48 pm 36 6.9 117 51.0 2.4 Coso Range, 5 mi. ESE of Haiwee Reservoir 9/4 9:14 pm 34 1.8 116 44.2 2.0 7 mi. SE of Mt. San Gorgonio 9/4 9:27 pm 36 6.9 117 51.2 2.5 5 mi. ESE of Haiwee Reservoir 9/4 9:29 pm 36 7.1 117 51.1 2.3 " 9/5 2:37 am 32 50.5 118 22.8 2.4 2 mi. NW of San Clemente Is. 9/5 5:34 am 34 6.9 116 55.1 2.4 5 mi. WNW of Mt. San Gorgonio 9/5 7:15 am 34 19.9 116 27.3 2.0 14 mi. N of Yucca Valley 9/5 9:24 am 36 6.4 117 51.6 3.4 5 mi. ESE of Haiwee Reservoir 9/5 9:38 am 36 6.8 117 50.7 2.4 " 9/5 1:16 pm 32 38.2 115 55.2 2.2 8 mi. SSE of Ocotillo 9/5 8:56 pm 36 7.0 117 51.0 2.4 5 mi. ESE of Haiwee Reservoir 9/5 9:33 pm 36 6.8 117 51.2 2.6 " 9/5 9:43 pm 36 6.9 117 50.8 2.2 " 9/5 11:21 pm 34 14.6 116 25.9 2.6 8 mi. N of Yucca Valley 9/6 4:13 am 36 7.4 117 50.7 2.1 5 mi. E of Haiwee Reservoir 9/6 9:22 am 35 49.4 117 42.3 2.1 14 mi. N of Ridgecrest 9/6 9:51 am 34 0.2 116 18.7 2.3 9 mi. S of Joshua Tree 9/6 9:52 am 35 49.4 117 42.2 2.0 14 mi. N of Ridgecrest 9/6 3:44 pm 35 49.4 117 42.4 2.0 " 9/6 8:55 pm 34 55.5 116 55.2 2.0 6 mi. ENE of Barstow 9/6 9:04 pm 34 55.6 116 55.3 2.7 " 9/7 12:11 am 33 29.2 116 27.6 2.2 13 mi. ESE of Anza 9/7 1:54 am 34 15.2 119 46.2 2.0 11 mi. SSE of Isla Vista 9/7 5:35 am 36 7.2 117 50.3 2.0 6 mi. ESE of Haiwee Reservoir 9/7 6:57 am 34 35.6 116 37.6 2.2 20 mi. ENE of Lucerne Valley 9/7 8:30 am 34 38.8 116 39.3 2.4 21 mi. NE of Lucerne Valley 9/7 11:25 am 34 2.3 117 7.2 2.0 3 mi. ESE of Redlands 9/7 9:28 pm 34 36.3 116 37.8 2.3 21 mi. ENE of Lucerne Valley 9/8 1:57 pm 36 6.4 117 51.4 2.2 5 mi. ESE of Haiwee Reservoir 9/8 3:02 pm 35 43.9 117 40.5 2.0 7 mi. N of Ridgecrest 9/8 3:40 pm 35 5.9 117 29.6 3.1 11 mi. NE of Boron 9/8 10:07 pm 35 5.8 117 29.7 2.3 " 9/9 3:57 am 35 46.8 117 39.2 2.5 10 mi. N of Ridgecrest 9/9 10:22 am 36 7.1 117 50.9 2.1 5 mi. ESE of Haiwee Reservoir 9/9 11:04 am 33 14.3 116 1.7 2.2 4 mi. SW of Salton City 9/9 10:00 pm 35 31.5 118 13.4 2.0 15 mi. ESE of town of Lake Isabella 9/9 10:43 pm 34 20.5 116 28.5 2.0 15 mi. N of Yucca Valley 9/10 12:15 am 35 6.0 117 29.6 2.9 11 mi. NE of Boron 9/10 4:23 am 34 30.4 116 31.8 2.6 27 mi. N of Yucca Valley 9/10 6:03 am 34 59.5 116 56.6 2.1 8 mi. NNE of Barstow 9/10 12:55 pm 34 37.1 116 45.5 2.2 16 mi. NE of Lucerne Valley 9/10 2:14 pm 35 49.4 117 42.4 2.4 14 mi. N of Ridgecrest 9/10 5:25 pm 35 47.9 117 37.9 3.7 12 mi. N of Ridgecrest 9/10 9:58 pm 33 17.6 115 41.8 2.2 4 mi. SSE of Bombay Beach 9/11 12:35 am 35 57.4 117 58.9 2.3 6 mi. SSW of Coso Junction 9/11 11:35 am 34 20.2 116 28.2 2.1 15 mi. N of Yucca Valley 9/11 1:22 pm 34 8.3 117 3.7 2.7 5 mi. SSE of Running Springs -------------------------------------------------------------