SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey May 2, 1996 Weekly Earthquake Report for Southern California ------------------------------------------------ April 25 - May 1, 1996 Prepared by: Nick Scheckel, Seismological Laboratory Debbie Wells, 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, April 25, Universal Time (ie. GMT), to midnight Wednesday night, May 1, Universal Time. In local time, the period of coverage is from 5 p.m., April 24, Pacific Daylight Time, to 5 p.m., May 1, Pacific Daylight Time. We detected and processed 349 earthquakes during the 7-day period covered. The largest and most widely felt earthquake this week occurred yesterday afternoon near Simi Valley. It registered a M4.1 and is considered an aftershock of the Northridge mainshock (M6.7, Jan. 17, 1994). This aftershock occurred on an east- striking thrust fault (like the Northridge mainshock) at a depth of 14 km. It was located at the northwest corner of the aftershock zone where many other aftershocks, including a M5.6 event 12 hours after the mainshock, have occurred. The last Northridge aftershock over a M4, happened only 6 weeks ago on March 20th. It too was a M4.1. The only M3 event this week went unfelt. It was a M3.3 Friday afternoon near North Shore, 10 miles northeast of the Salton Sea. This is part of a swarm that produced two earthquakes above magnitude 3 last week. An earthquake was felt in west Los Angeles on Saturday morning, but it was only a M2.5 near Culver City. Even smaller were the three earthquakes (M2.3,2.0,2.3) that occurred west of the Los Angeles airport on Monday, none of which were felt. 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 ------------------------------------------------------------- 4/24 10:14 pm 35 48.0 117 35.4 2.1 13 mi. NNE of Ridgecrest 4/25 3:45 am 35 48.1 117 35.4 2.0 " 4/25 3:45 am 35 48.3 117 35.6 2.0 " 4/25 9:10 am 34 8.7 116 25.7 2.0 2 mi. NNE of Yucca Valley 4/25 2:08 pm 34 58.0 116 56.7 2.3 7 mi. NE of Barstow 4/25 3:38 pm 32 46.3 115 32.7 2.0 1 mi. SSE of El Centro 4/25 5:07 pm 35 31.8 116 14.4 2.1 20 mi. NNW of Baker 4/25 5:56 pm 36 4.9 120 38.6 2.7 17 mi. NW of Parkfield 4/25 6:15 pm 34 25.1 121 0.9 2.8 23 mi. WSW of Pt. Arguello 4/26 1:58 am 34 27.4 116 30.3 2.1 23 mi. N of Yucca Valley 4/26 2:19 am 34 17.6 118 27.4 2.0 1 mi. WNW of Pacoima 4/26 12:14 pm 33 44.2 115 55.3 3.3 14 mi. N of North Shore 4/26 2:31 pm 33 15.4 118 19.7 2.2 5 mi. S of Avalon, Catalina Island 4/27 4:59 am 33 58.1 116 46.0 2.1 3 mi. NNE of Cabazon 4/27 5:22 am 33 44.0 115 55.2 2.1 14 mi. N of North Shore 4/27 6:04 am 33 59.9 118 24.2 2.5 Under Culver City 4/27 8:16 am 34 9.2 116 25.0 2.2 2 mi. NNE of Yucca Valley 4/27 10:07 am 33 44.2 115 55.2 2.3 14 mi. N of North Shore 4/27 10:14 am 33 44.2 115 55.2 2.1 " 4/27 2:21 pm 33 55.0 117 3.8 2.2 5 mi. W of Beaumont 4/27 3:09 pm 33 44.2 115 55.2 2.1 14 mi. N of North Shore 4/27 3:21 pm 32 46.6 115 33.5 2.2 1 mi. SSW of El Centro 4/27 3:35 pm 35 48.3 117 38.8 2.0 12 mi. N of Ridgecrest 4/28 4:15 am 33 0.6 117 51.2 2.4 32 mi. SSW of Dana Point 4/28 7:16 am 35 44.9 117 37.4 2.2 9 mi. NNE of Ridgecrest 4/28 8:59 am 33 44.2 115 55.2 2.9 14 mi. N of North Shore 4/28 9:51 am 35 47.3 117 40.2 2.6 11 mi. N of Ridgecrest 4/28 12:29 pm 33 44.2 115 55.2 2.0 14 mi. N of North Shore 4/28 6:01 pm 33 3.5 115 55.0 2.0 15 mi. S of Salton City 4/28 6:38 pm 35 44.7 117 37.6 2.6 8 mi. NNE of Ridgecrest 4/29 5:02 am 34 9.2 116 25.8 2.2 2 mi. NNE of Yucca Valley 4/29 10:00 am 34 29.4 116 32.6 2.0 23 mi. NE of Big Bear City 4/29 10:05 am 33 54.8 118 30.4 2.3 4 mi. WSW of Los Angeles Airport 4/29 11:08 am 34 28.7 118 0.1 2.3 9 mi. SE of Palmdale 4/29 2:48 pm 35 20.9 118 37.0 2.1 15 mi. NE of Arvin 4/29 4:49 pm 33 38.8 116 43.8 2.0 6 mi. S of Idyllwild 4/29 7:07 pm 32 45.2 118 18.3 2.6 5 mi. SSE of San Clemente Is. 4/29 8:29 pm 34 38.5 116 0.4 2.0 34 mi. N of Twentynine Palms 4/29 8:50 pm 33 54.4 118 29.9 2.0 4 mi. SW of Los Angeles Airport 4/29 8:56 pm 33 54.9 118 29.8 2.3 4 mi. WSW of Los Angeles Airport 4/30 1:00 am 33 1.0 117 49.6 2.1 31 mi. SSW of Dana Point 4/30 2:46 am 34 17.8 118 27.8 2.1 1 mi. WNW of Pacoima 4/30 4:15 am 34 17.8 116 27.5 2.0 12 mi. N of Yucca Valley 4/30 4:16 am 34 20.5 116 28.1 2.1 15 mi. N of Yucca Valley 4/30 3:13 pm 34 16.2 118 27.7 2.4 1 mi. SW of Pacoima 5/ 1 1:40 am 35 55.8 118 20.7 2.0 21 mi. NNE of town of Lake Isabella 5/ 1 12:49 pm 34 21.2 118 42.1 4.1 5 mi. N of Simi Valley -------------------------------------------------------------