SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey February 29, 1996 Weekly Earthquake Report for Southern California ------------------------------------------------ February 22 - 28, 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, February 22, Universal Time (ie. GMT), to midnight Wednesday night, February 28, Universal Time. In local time, the period of coverage is from 4 p.m., February 21 to 4 p.m., February 28, Pacific Standard Time. We detected and processed 368 earthquakes during the 7-day period covered. There were three quakes above M3 this week, and all three were felt. The first occurred on Saturday morning near Fontana, with a magnitude of M3.4. It was not an aftershock. It's focal mechanism was strike-slip, with planes striking northwest and northeast. The location was within the northeast-striking Fontana trend, which is a notable trend of microseismicity assumed to be related to a buried fault in the San Bernardino Valley. We tentatively associate this week's event with that buried, left-lateral strike-slip fault. Then, late Tuesday afternoon, there was a M3.3 in Mexico but apparently felt slightly in the Imperial Valley. The third noticed event was a Northridge aftershock in the wee hours of Wednesday morning, near Pacoima. It had a magnitude of M3.0 and a mechanism showing a combination of strike slip and thrust. 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 ------------------------------------------------------------- 2/22 5:48 am 34 23.5 116 27.7 2.4 18 mi. N of Yucca Valley 2/22 4:09 pm 34 7.2 116 59.8 2.5 6 mi. NNE of Yucaipa 2/22 10:50 pm 34 20.8 116 28.6 2.4 15 mi. N of Yucca Valley 2/23 1:11 am 33 22.2 116 17.7 2.5 9 mi. NNE of Borrego Springs 2/23 1:42 am 33 12.4 116 46.8 2.1 2 mi. SSW of Lake Henshaw 2/23 6:06 am 34 31.4 116 33.0 2.0 24 mi. NE of Big Bear 2/23 9:20 am 33 7.8 118 46.0 2.3 11 mi. NW of San Clemente Is. 2/23 2:07 pm 33 7.6 118 47.3 2.3 " 2/23 2:08 pm 34 22.2 116 28.1 2.1 17 mi. N of Yucca Valley 2/23 3:00 pm 34 22.0 116 28.0 2.6 " 2/23 3:07 pm 33 49.8 117 29.5 2.2 5 mi. SE of Corona 2/24 12:01 am 36 10.8 118 18.3 2.2 18 mi. WSW of Olancha 2/24 3:56 am 35 0.6 116 57.9 2.0 9 mi. NNE of Barstow 2/24 4:24 am 34 22.0 116 27.9 2.0 17 mi. N of Yucca Valley 2/24 10:57 am 34 5.9 117 29.5 3.4 3 mi. W of Fontana FELT 2/24 11:34 am 32 19.7 115 21.6 2.5 24 mi. SSE of Calexico 2/24 12:12 pm 35 44.6 116 28.7 2.1 19 mi. SW of Shoshone 2/24 4:17 pm 34 23.3 116 27.6 2.2 18 mi. N of Yucca Valley 2/25 6:29 am 34 21.9 116 28.3 2.0 " 2/25 11:22 am 35 47.2 117 38.3 2.0 11 mi. N of Ridgecrest 2/25 2:52 pm 34 23.0 116 27.0 2.1 18 mi. N of Yucca Valley 2/25 5:19 pm 34 24.5 116 28.0 2.0 20 mi. N of Yucca Valley 2/25 6:53 pm 35 49.0 117 41.0 2.0 13 mi. N of Ridgecrest 2/25 9:36 pm 33 30.8 116 27.7 2.1 12 mi. ESE of Anza 2/25 10:17 pm 34 9.0 116 24.3 2.3 3 mi. NE of Yucca Valley 2/26 1:39 am 34 58.5 116 57.3 2.4 7 mi. NNE of Barstow 2/26 2:36 am 34 27.4 116 30.0 2.0 23 mi. N of Yucca Valley 2/26 6:09 am 34 37.3 116 36.4 2.3 22 mi. ENE of Lucerne Valley 2/26 10:17 am 35 44.1 117 37.9 2.1 8 mi. NNE of Ridgecrest 2/26 1:23 pm 35 46.7 117 39.3 2.2 10 mi. N of Ridgecrest 2/26 1:24 pm 35 46.7 117 39.4 2.5 " 2/26 6:03 pm 34 55.2 116 54.5 2.0 6 mi. ENE of Barstow 2/27 2:17 am 33 0.5 117 44.2 2.2 24 mi. WSW of Oceanside 2/27 2:53 am 33 0.2 117 44.2 2.2 " 2/27 5:59 pm 32 18.9 115 13.4 3.3 29 mi. SSE of Calexico FELT 2/27 7:28 pm 32 39.2 118 8.2 2.0 16 mi. SE of San Clemente Is. 2/28 1:59 am 34 16.0 118 25.2 3.0 1 mi. SE of Pacoima FELT 2/28 6:08 am 35 43.7 117 37.3 2.5 7 mi. NNE of Ridgecrest 2/28 10:51 am 34 26.8 116 30.0 2.3 22 mi. N of Yucca Valley -------------------------------------------------------------