SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey November 7, 1996 Weekly Earthquake Report for Southern California ------------------------------------------------ October 31 - November 6, 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 818-395-6327. For daily updates, call our Earthquake Information Hotline: 818-395-6977. -------------------------------- This week's Report covers the time period from midnight Thursday morning, October 31, Universal Time (ie. GMT), to midnight Wednesday night, November 6, Universal Time. In local time, the period of coverage is from 5 p.m., October 30, Pacific Daylight Time, to 5 p.m., November 6, Pacific Daylight Time. We detected and processed 203 earthquakes during the seven-day period covered. In terms of total numbers, the seismicity was low again this week. There were, however, five M3+ quakes (demonstrating again true random fluctuations. We have had other weeks with higher total numbers and no M3 events. It all averages out.) Three of these M3+ events were Landers aftershocks, and two were in the Imperial Valley. The Landers aftershocks included 1) a M3.3 on Friday morning, 2) a M3.3 on Saturday night, and 3) a M3.1 on Sunday evening. The Sunday evening quake was near Yucca Valley and was felt. The first two had focal mechanisms similar to the June 28, 1992 Mw7.3 mainshock, on north-northwest-striking right-lateral strike-slip faults. The third event had a normal faulting mechanism with northeast-striking faults. Many small normal faults have been mapped in the Mojave desert. The two M3+'s in Imperial Valley were: an Obsidian Butte quake of M3.0 on Friday evening and a M3.0 Westmorland quake on Saturday morning. The latter was felt, and it had a M2.5 after- shock that was also felt. All of these occurred in the Brawley Seismic Zone, which is a band of higher seismicity connecting the northern end of the Imperial Fault with the southern end of the San Andreas. As with other earthquakes in the Brawley Seismic Zone, the Obsidian Butte event showed San-Andreas-type strike-slip faulting in its mechanism. 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 ------------------------------------------------------------- 10/30 6:34 pm 34 35.7 116 16.9 2.2 31 mi. N of Joshua Tree 10/31 3:33 pm 34 35.9 116 16.7 2.1 " 10/31 3:51 pm 34 19.1 116 27.6 2.2 13 mi. N of Yucca Valley 11/1 12:59 am 34 35.7 116 16.6 2.2 31 mi. N of Joshua Tree 11/1 9:57 am 34 20.4 116 27.0 3.3 15 mi. N of Yucca Valley 11/1 7:04 pm 33 12.4 115 42.2 3.0 4 mi. WNW of Obsidian Butte 11/2 5:50 am 34 37.5 116 39.8 2.3 20 mi. NE of Lucerne Valley 11/2 11:17 am 33 0.1 115 34.8 3.0 3 mi. SE of Westmorland FELT 11/2 11:33 am 32 59.9 115 34.6 2.5 " FELT 11/2 11:56 am 35 57.3 117 39.9 2.2 16 mi. ESE of Coso Junction 11/2 12:37 pm 33 0.3 115 34.3 2.0 3 mi. NW of Brawley 11/2 12:49 pm 33 0.1 115 34.4 2.2 " 11/2 3:00 pm 34 59.3 116 57.0 2.1 7 mi. NNE of Barstow 11/2 10:32 pm 34 35.7 116 16.8 3.3 31 mi. N of Joshua Tree 11/2 10:43 pm 34 35.5 116 17.0 2.0 " 11/3 6:13 pm 34 8.5 116 25.7 3.1 1 mi. NNE of Yucca Valley FELT 11/4 3:05 am 33 31.6 115 51.6 2.1 4 mi. E of North Shore 11/4 7:23 am 34 19.4 116 27.8 2.1 14 mi. N of Yucca Valley 11/4 4:01 pm 34 19.5 116 27.5 2.2 " 11/4 5:00 pm 32 58.8 117 36.4 2.2 19 mi. SW of Oceanside 11/5 7:21 am 33 0.2 117 44.5 2.0 24 mi. WSW of Oceanside 11/5 7:39 am 34 18.3 116 26.1 2.1 12 mi. N of Yucca Valley 11/5 7:49 am 32 23.3 115 24.1 2.5 20 mi. SSE of Calexico 11/5 9:48 am 35 45.5 117 38.7 2.6 9 mi. N of Ridgecrest 11/5 2:16 pm 36 5.4 117 54.6 2.1 3 mi. SSE of Haiwee Reservoir 11/5 4:00 pm 33 0.4 117 43.6 2.0 23 mi. WSW of Oceanside -------------------------------------------------------------