SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey February 20, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ February 13 - 19, 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 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, February 13, Universal Time (ie. GMT), to midnight Wednesday night, February 19, Universal Time. In local time, the period of coverage is from 4 p.m., February 12, Pacific Standard Time, to 4 p.m., February 19, Pacific Standard Time. We detected and processed 275 earthquakes during the seven-day period covered. There was a small resurgence of the Coso aftershocks this week, particularly on Friday and Saturday. This activity included a M3.8 on Friday evening and a M3.7 just after mid- night on Saturday. All the events occured very close to the M5.3 mainshock of last November 27. As with most of the earthquakes in this sequence, these were strike-slip. Aside from the Coso quakes, the largest event was a M3.1 in the Ontario area on Saturday morning. This quake also had a standard California strike-slip mechanism (right-lateral on a northwest plane or left-lateral on a northeast plane). Oddly enough, we did not get any inquiries about any of these M3+ quakes, although a much smaller M2.3 on Tuesay, under Claremont, was reported felt. 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 ------------------------------------------------------------- 2/13 12:41 am 34 9.4 116 25.5 2.3 2 mi. NNE of Yucca Valley 2/13 11:52 am 34 54.3 116 44.1 2.5 16 mi. E of Barstow 2/13 2:52 pm 34 29.2 116 30.4 2.4 25 mi. N of Yucca Valley 2/14 3:09 am 36 58.2 117 28.9 2.7 31 mi. NW of Stovepipe Wells 2/14 4:42 am 36 3.8 117 38.4 2.1 17 mi. E of Coso Junction 2/14 6:53 am 34 19.9 118 27.3 2.4 3 mi. NNW of San Fernando 2/14 6:56 am 32 46.4 115 27.1 2.0 6 mi. ESE of El Centro 2/14 8:33 am 36 4.5 117 39.1 2.2 16 mi. E of Coso Junction 2/14 11:01 am 34 29.5 118 3.7 2.4 6 mi. SSE of Palmdale 2/14 8:06 pm 36 4.3 117 38.3 2.9 17 mi. E of Coso Junction 2/14 8:08 pm 36 5.1 117 38.3 2.2 " 2/14 8:12 pm 36 4.5 117 38.1 2.1 " 2/14 8:16 pm 36 4.5 117 38.1 2.7 " 2/14 8:16 pm 33 14.2 116 40.5 2.3 5 mi. E of Lake Henshaw 2/14 8:22 pm 36 4.3 117 38.0 3.8 17 mi. E of Coso Junction 2/14 8:26 pm 36 4.8 117 38.1 2.0 " 2/14 8:29 pm 36 5.5 117 38.4 2.5 " 2/14 8:40 pm 36 5.0 117 38.3 2.0 " 2/14 8:59 pm 36 5.1 117 38.2 2.9 " 2/14 9:11 pm 36 4.7 117 38.3 2.6 " 2/14 11:31 pm 36 4.4 117 38.1 2.7 " 2/14 11:33 pm 36 4.7 117 38.0 2.0 " 2/15 12:06 am 36 4.8 117 38.1 2.1 " 2/15 12:13 am 36 5.1 117 38.2 3.7 " 2/15 12:23 am 36 4.6 117 38.1 2.4 " 2/15 12:27 am 36 5.1 117 38.2 2.8 " 2/15 12:40 am 36 4.6 117 38.1 2.4 " 2/15 12:55 am 36 4.3 117 38.3 2.5 " 2/15 1:33 am 36 5.0 117 38.1 2.2 " 2/15 2:43 am 36 4.6 117 37.8 2.0 " 2/15 3:35 am 36 5.2 117 38.0 2.3 " 2/15 5:12 am 33 11.3 115 36.4 2.0 2 mi. NE of Obsidian Butte 2/15 5:36 am 36 4.2 117 38.0 2.1 17 mi. E of Coso Junction 2/15 5:40 am 36 4.9 117 37.6 2.4 18 mi. E of Coso Junction 2/15 5:40 am 34 29.8 118 3.6 2.7 6 mi. SSE of Palmdale 2/15 5:44 am 36 4.6 117 38.2 2.2 17 mi. E of Coso Junction 2/15 5:46 am 36 4.3 117 37.9 2.7 " 2/15 5:51 am 36 4.2 117 37.8 2.2 " 2/15 6:11 am 36 4.9 117 38.0 2.6 " 2/15 6:23 am 33 59.8 117 34.8 2.4 6 mi. SE of Ontario 2/15 6:57 am 36 4.7 117 38.2 2.0 17 mi. E of Coso Junction 2/15 7:14 am 33 60.0 117 34.9 3.1 5 mi. SE of Ontario 2/15 7:45 am 36 4.2 117 38.0 2.1 17 mi. E of Coso Junction 2/15 8:59 am 36 4.2 117 38.0 2.1 " 2/15 9:41 am 34 9.6 116 25.5 2.0 3 mi. NNE of Yucca Valley 2/15 12:58 pm 33 45.3 118 5.4 2.2 1 mi. NE of Seal Beach 2/15 5:26 pm 36 4.0 117 37.7 2.4 17 mi. E of Coso Junction 2/15 5:34 pm 36 3.4 117 38.0 2.0 " 2/15 8:04 pm 34 25.4 116 28.6 2.0 21 mi. N of Yucca Valley 2/15 10:06 pm 34 19.6 120 27.7 2.0 9 mi. S of Pt. Conception 2/16 6:16 am 36 4.2 117 37.9 2.1 17 mi. E of Coso Junction 2/16 7:32 am 34 21.8 119 51.6 2.0 3 mi. S of Isla Vista 2/16 2:15 pm 33 58.0 116 39.7 2.1 7 mi. SW of Morongo Valley 2/16 4:19 pm 33 20.9 116 20.7 2.0 6 mi. NNE of Borrego Springs 2/16 10:40 pm 36 5.2 117 39.4 2.0 16 mi. E of Coso Junction 2/17 1:55 am 33 55.1 120 10.8 2.5 4 mi. WSW of Santa Rosa Is. 2/17 2:58 pm 34 22.8 118 37.5 2.2 3 mi. WSW of Valencia 2/18 5:59 am 34 7.6 118 32.4 2.0 3 mi. SW of Encino 2/18 6:35 am 33 16.3 116 8.9 2.0 8 mi. N of Ocotillo Wells 2/18 12:56 pm 34 5.8 117 44.1 2.3 Under Claremont Colleges FELT 2/18 5:44 pm 32 57.7 117 40.2 2.1 23 mi. SW of Oceanside 2/18 6:12 pm 32 24.0 115 11.9 2.8 25 mi. SE of Calexico 2/18 8:49 pm 33 15.7 116 0.6 2.4 2 mi. WSW of Salton City 2/19 7:57 am 36 4.0 117 38.7 2.1 17 mi. E of Coso Junction 2/19 8:00 am 33 11.4 115 33.7 2.2 4 mi. SW of Niland 2/19 12:43 pm 33 40.2 117 57.5 2.1 3 mi. S of Fountain Valley -------------------------------------------------------------