SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey December 14, 1995 Weekly Earthquake Report for Southern California ------------------------------------------------ December 7 - 13, 1995 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, December 7, Universal Time (ie. GMT), to midnight Wednesday night, December 13, 1995, Universal Time. In local time, the period of coverage is from 4 p.m., December 6 to 4 p.m., December 13 Pacific Standard Time. We detected and processed 397 earthquakes during the 7-day period covered. Total seismicity this week was more than 100 events less than any week since the Ridgecrest sequence began this past August. This number reflects a decrease in the number of Ridgecrest quakes, along with the continued gradual decline of the Northridge (January 17, '94 Mw6.7) and Landers (June 28, '92 Mw7.3) aftershock sequences. This week was also slightly unusual in that all the quakes about M3 occurred in the general Santa Monica Mountain and Ventura Basin area, and all happened during a 52 hour period late last week. The activity in question began early last Thursday morning, with a M3.3 at the western edge of the Northridge aftershock zone, near Simi Valley. The next morning there was a M3.4 west of Fillmore. The latter had a M2.9 aftershock in the afternoon. Then on Friday evening, there was a M3.5 along the coast to the west of Malibu. That quake had a M3.0 aftershock early the next morning. All these quakes had thrust focal mechanisms, except for the Simi Valley one, where there was also a significant strike-slip component to the motion. There was one more earthquake felt; it was a M2.8 near Bolsa Chica beach on Sunday evening. The table 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 ------------------------------------------------------------- 12/6 4:13 pm 34 22.7 116 27.7 2.1 18 mi. N of Yucca Valley 12/6 4:16 pm 34 22.6 116 27.6 2.4 17 mi. N of Yucca Valley 12/6 5:01 pm 35 47.4 117 39.5 2.2 11 mi. N of Ridgecrest 12/6 7:16 pm 34 37.2 116 34.3 2.3 24 mi. ENE of Lucerne Valley 12/7 2:01 am 34 17.1 118 40.7 3.3 1 mi. ENE of Simi Valley FELT 12/7 4:31 am 33 10.7 115 36.4 2.1 1 mi. ENE of Obsidian Butte 12/7 9:25 am 34 22.6 119 3.0 3.4 7 mi. W of Fillmore FELT 12/7 3:01 pm 34 22.6 119 2.5 2.9 " 12/7 3:33 pm 33 43.5 118 54.1 2.1 19 mi. SSW of Pt. Dume 12/7 4:26 pm 34 0.9 116 19.3 2.1 8 mi. S of Joshua Tree 12/8 9:03 am 35 46.6 117 38.8 2.4 10 mi. N of Ridgecrest 12/8 8:15 pm 34 2.1 118 56.2 3.5 Under Leo Carrillo State Beach; FELT 12/8 8:27 pm 34 37.3 116 34.0 2.1 24 mi. ENE of Lucerne Valley 12/8 9:36 pm 35 46.4 117 39.5 2.0 10 mi. N of Ridgecrest 12/9 12:56 am 35 30.0 119 16.9 2.2 18 mi. WNW of Bakersfield 12/9 1:32 am 34 22.4 119 4.2 2.4 8 mi. W of Fillmore 12/9 6:09 am 34 2.3 118 56.3 3.0 Under Leo Carrillo State Beach; FELT 12/9 4:39 pm 35 45.4 117 38.0 2.0 9 mi. N of Ridgecrest 12/10 6:18 am 33 23.7 116 55.0 2.1 4 mi. NW of Palomar Observatory 12/10 11:25 am 35 34.8 118 23.0 2.0 6 mi. SE of town of Lake Isabella 12/10 11:26 am 34 30.6 118 39.9 2.2 2 mi. WSW of Castaic Lake dam 12/10 2:50 pm 33 59.7 117 12.0 2.8 4 mi. SSW of Redlands 12/10 7:58 pm 33 39.7 118 3.1 2.8 1 mi. SSW of Bolsa Chica Beach; FELT 12/11 3:10 am 35 43.5 117 37.4 2.3 7 mi. NNE of Ridgecrest 12/11 4:21 am 35 44.7 117 38.1 2.1 8 mi. NNE of Ridgecrest 12/11 10:14 am 35 46.6 117 39.0 2.1 10 mi. N of Ridgecrest 12/11 10:49 am 34 22.1 116 28.0 2.1 17 mi. N of Yucca Valley 12/11 2:21 pm 35 43.4 117 37.3 2.0 7 mi. NNE of Ridgecrest 12/11 9:07 pm 34 11.5 116 26.1 2.0 5 mi. N of Yucca Valley 12/11 11:00 pm 33 0.4 117 44.4 2.6 24 mi. WSW of Oceanside 12/11 11:29 pm 33 0.3 117 44.4 2.5 " 12/12 1:42 am 35 44.4 117 37.8 2.5 8 mi. NNE of Ridgecrest 12/12 10:38 am 35 55.5 117 56.8 2.0 8 mi. S of Coso Junction 12/12 3:09 pm 33 56.3 116 38.1 2.1 7 mi. SSW of Morongo Valley 12/12 4:19 pm 35 44.4 117 40.3 2.0 8 mi. N of Ridgecrest 12/12 11:18 pm 34 14.2 116 44.9 2.1 6 mi. ESE of Big Bear City 12/13 2:47 am 34 13.9 117 30.1 2.0 5 mi. W of Devore 12/13 5:28 am 34 9.6 116 25.6 2.0 3 mi. NNE of Yucca Valley 12/13 8:38 am 35 46.0 117 38.7 2.1 10 mi. N of Ridgecrest 12/13 3:45 pm 34 38.3 116 32.7 2.4 26 mi. ENE of Lucerne Valley -------------------------------------------------------------