December 11, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ December 4 - 10, 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 626-395-6327. For daily updates, call our Earthquake Information Hotline: 626-395-6977. -------------------------------- This week's Report covers the time period from midnight Thursday morning, December 4 Universal Time (ie. UTC), to midnight Wednesday night, December 10, Universal Time. In local time, the period of coverage is from 4 p.m., December 3, Pacific Standard Time, to 4 p.m., December 10, Pacific Standard Time. detected 206 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 largest quake of the week and the only one felt was a M4.1 that occurred on Friday morning in the Yucaipa area. It had a strike-slip focal mechanism and was probably on the north branch of the San Andreas Fault. However, since this location showed an increase in activity at the time of the Landers/Big Bear quakes in 1992, it is technically and aftershock. It was widely felt in the Inland Empire area. There were several after- shocks of the M4.1; none generated any inquiries. In addition to the Yucaipa activity, we also saw continued activity at Obsidian Butte in the Imperial Valley from the previous week, the largest this week being a M3.3 on Thursday. There were also M3+ events in the Coalinga area (see the Menlo Park report) and south of the U.S./Mexico border. 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 ------------------------------------------------------------- 12/3 4:49 pm 33 9.6 115 38.8 2.0 Under Obsidian Butte, Imperial Valley 12/3 5:22 pm 32 58.9 115 46.6 2.1 9 mi. WSW of Westmorland 12/4 12:30 am 33 9.8 115 39.3 3.3 Under Obsidian Butte 12/4 12:33 am 33 9.5 115 38.7 2.1 " 12/4 12:47 am 33 9.6 115 38.8 2.2 " 12/4 12:54 am 33 9.7 115 38.8 2.1 " 12/4 1:16 am 34 17.9 118 26.9 2.6 1 mi. NW of San Fernando 12/4 2:01 am 33 9.6 115 38.9 2.8 Under Obsidian Butte 12/4 4:46 am 36 55.4 118 15.1 2.4 8 mi. NNW of Independence 12/4 4:54 am 33 10.7 116 2.9 2.3 5 mi. ENE of Ocotillo Wells 12/4 10:56 am 35 5.0 117 29.3 2.0 10 mi. ENE of Boron 12/4 2:23 pm 36 22.5 117 24.6 2.2 21 mi. SW of Stovepipe Wells 12/5 9:04 am 34 5.8 116 59.7 4.1 4 mi. NNE of Yucaipa FELT 12/5 9:09 am 34 6.0 116 59.8 2.5 " 12/5 11:01 am 34 5.7 116 59.9 2.9 " 12/5 2:16 pm 34 5.8 116 59.6 2.1 " 12/6 12:07 am 34 0.8 117 12.2 2.7 3 mi. SSW of Redlands 12/6 2:34 am 36 23.6 120 16.0 3.3 18 mi. NNE of Coalinga 12/6 2:58 am 36 2.7 117 34.9 2.3 22 mi. NNW of Trona 12/6 10:33 am 34 55.2 116 32.4 2.3 27 mi. E of Barstow 12/6 7:19 pm 34 0.7 117 5.1 2.0 3 mi. WSW of Yucaipa 12/6 11:16 pm 35 44.4 118 2.1 2.3 21 mi. SSW of Coso Junction 12/7 5:21 am 35 59.6 119 46.4 2.0 35 mi. SW of Visalia 12/7 2:45 pm 32 24.5 116 18.7 2.7 29 mi. SW of Ocotillo 12/7 10:00 pm 35 39.3 118 23.5 2.0 4 mi. ENE of town of Lake Isabella 12/8 5:37 am 33 20.9 116 21.6 2.0 6 mi. N of Borrego Springs 12/8 7:17 am 34 57.3 116 47.1 2.0 14 mi. ENE of Barstow 12/8 5:10 pm 32 20.2 115 15.8 3.6 26 mi. SSE of Calexico 12/8 5:52 pm 32 20.3 115 15.2 3.0 " 12/8 9:42 pm 32 19.9 115 14.8 2.8 " 12/9 2:58 am 34 2.9 116 24.0 2.2 5 mi. SSE of Yucca Valley 12/9 6:30 am 36 19.0 120 22.7 3.1 12 mi. N of Coalinga 12/9 11:42 am 36 6.1 120 12.1 2.6 9 mi. ESE of Coalinga 12/9 1:46 pm 33 59.8 117 6.6 2.4 5 mi. WSW of Yucaipa 12/9 2:29 pm 35 44.4 117 37.5 2.6 8 mi. NNE of Ridgecrest 12/9 3:25 pm 34 3.0 116 23.8 2.0 5 mi. SSE of Yucca Valley 12/9 9:14 pm 36 23.1 120 34.7 2.9 20 mi. NW of Coalinga 12/10 3:12 am 36 4.8 117 38.5 2.3 17 mi. E of Coso Junction 12/10 5:16 am 32 28.0 115 23.2 2.3 15 mi. SSE of Calexico 12/10 5:25 am 32 28.4 115 23.0 3.0 " 12/10 5:29 am 32 28.2 115 23.3 2.5 " 12/10 5:33 am 32 28.9 115 23.0 2.9 " 12/10 9:55 am 34 21.7 116 28.0 2.6 16 mi. N of Yucca Valley 12/10 10:14 am 36 4.1 117 53.0 2.4 4 mi. ENE of Coso Junction 12/10 11:02 am 36 46.1 119 54.7 2.6 7 mi. WNW of Fresno 12/10 11:19 am 35 45.8 117 38.6 2.0 9 mi. N of Ridgecrest -------------------------------------------------------------