March 17, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ March 10 - 16, 1994 Prepared by: Kate Hutton, Seismological Laboratory (kate@bombay.gps.caltech.edu) Lucy Jones, U.S. Geological Survey California Institute of Technology This document is a commentary on current seismic activity. The earthquakes discussed have been detected and processed automatically. All epicenters and magnitudes have been reviewed to exclude obvious blunders; however, they must still be considered preliminary. 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, March 10, Pacific Standard Time, to midnight Wednesday night, March 16, Pacific Standard Time. There are 461 this week. Although a number of Northridge aftershocks were large enough to be felt, the rate continues to decline. For the first time in two months (Yes, today is the two month anniversary!), we are able to list all the M2.0 and larger quakes, aftershocks included, in the table. Hopefully, the rate will remain low enough that we can continue to do this. The total earthquake rate on Tuesday (March 15) might have been slightly higher than what we recorded, since our network was seriously affected by a fire at the Bunker Hill telephone switch. The week's largest quake occurred in the early morning, last Thursday. It was a Northridge aftershock measuring M3.5. Outside of the aftershock sequence, there was a M3.0 quake in the Loma Linda area of Monday morning that was felt. Of slight interest is the small swarm at Obsidian Butte, a few miles southwest of Niland. This is an often active area, having produced quakes above M4.0 in the past few years, usually as members of swarms. Swarms are groups of earthquakes at the (more or less) same location where no single event stands out as a clear main shock. A small swarm is often called a cluster. The table lists the quakes 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 8 hrs, to the Pacific Standard Time listed. Table 1 ------- Date Time N Lat. W Long. Mag ------------------------------------------------------------- 3/10 12:01 am 34 16.2 118 28.9 2.2 2 mi. WSW of San Fernando 3/10 4:44 am 34 19.7 118 34.7 3.5 4 mi. SW of Newhall; FELT 3/10 8:44 am 34 8.1 117 26.9 2.0 2 mi. NNW of Fontana 3/10 9:09 am 34 26.4 119 20.3 2.0 5 mi. W of Ojai 3/10 10:22 am 34 13.7 116 26.3 2.0 7 mi. N of Yucca Valley 3/10 1:57 pm 34 13.6 118 33.9 2.2 1 mi. WSW of Northridge 3/10 2:48 pm 34 15.0 118 39.3 2.4 3 mi. ESE of Simi Valley 3/10 3:24 pm 34 57.2 116 54.3 2.0 8 mi. ENE of Barstow 3/10 4:48 pm 34 22.2 116 26.9 2.0 17 mi. N of Yucca Valley 3/10 4:48 pm 34 21.9 116 27.0 2.5 " 3/10 4:52 pm 34 58.4 116 48.2 2.0 13 mi. ENE of Barstow 3/10 4:56 pm 34 7.1 116 55.8 2.0 6 mi. WNW of Mt. San Gorgonio 3/10 9:03 pm 34 17.3 118 25.7 2.1 Under San Fernando 3/10 9:38 pm 34 19.2 118 35.1 3.1 5 mi. SW of Newhall; FELT 3/10 9:39 pm 34 18.9 118 26.7 2.1 2 mi. N of San Fernando 3/10 11:19 pm 34 12.4 118 38.3 2.4 1 mi. WNW of Canoga Park 3/11 3:29 am 34 19.5 118 34.7 2.2 4 mi. SW of Newhall 3/11 5:55 am 34 18.8 118 33.1 3.1 4 mi. SSW of Newhall 3/11 5:56 am 34 19.1 118 33.5 2.7 " 3/11 6:01 am 34 19.0 118 33.2 2.3 " 3/11 6:15 am 34 18.6 118 33.2 2.0 " 3/11 7:59 am 34 18.6 118 32.9 2.4 " 3/11 8:46 am 33 11.8 115 34.2 2.7 Obsidian Butte, 4 mi. SW of Niland; FELT 3/11 8:47 am 33 10.9 115 34.9 2.0 " 3/11 8:51 am 33 10.9 115 33.6 2.0 " 3/11 8:59 am 33 12.2 115 32.9 2.1 2 mi. SW of Niland 3/11 9:05 am 33 10.1 115 33.6 2.2 4 mi. SW of Niland 3/11 9:11 am 34 18.4 118 32.5 2.0 4 mi. N of Northridge 3/11 9:39 am 33 15.4 116 22.1 2.0 Under Borrego Springs 3/11 9:45 am 34 15.2 118 27.7 2.0 2 mi. SSW of San Fernando 3/11 10:18 am 34 18.3 118 32.9 2.1 4 mi. N of Northridge 3/11 10:35 am 34 12.5 118 33.3 2.4 2 mi. SSW of Northridge 3/11 2:48 pm 34 17.2 118 30.5 2.9 3 mi. NNE of Northridge 3/11 6:25 pm 34 9.6 116 26.3 2.4 2 mi. N of Yucca Valley 3/11 6:25 pm 34 9.6 116 26.8 2.6 " 3/11 8:16 pm 33 11.5 115 34.2 2.0 4 mi. SW of Niland 3/11 9:44 pm 35 38.7 117 38.1 2.1 2 mi. NE of Ridgecrest 3/11 11:11 pm 34 35.5 116 36.6 2.1 21 mi. ENE of Lucerne Valley 3/11 11:50 pm 34 37.4 116 34.2 2.0 24 mi. ENE of Lucerne Valley 3/12 12:12 am 34 17.2 118 27.3 2.0 Under San Fernando 3/12 1:08 am 34 22.7 118 41.8 2.1 6 mi. N of Simi Valley 3/12 1:32 pm 34 13.3 118 36.2 2.2 1 mi. N of Canoga Park 3/12 1:45 pm 34 13.7 118 36.5 2.8 1 mi. N of Canoga Park; FELT 3/12 3:08 pm 34 21.8 116 28.2 2.3 16 mi. N of Yucca Valley 3/12 3:26 pm 33 37.1 118 20.8 2.5 6 mi. SSW of Pt. Fermin, San Pedro 3/12 3:27 pm 34 17.7 118 27.7 2.2 1 mi. NW of San Fernando 3/12 5:03 pm 34 20.6 118 30.6 2.1 2 mi. SSE of Newhall 3/12 5:44 pm 35 0.8 116 58.2 2.0 9 mi. NNE of Barstow 3/12 7:12 pm 34 23.4 116 27.6 2.8 18 mi. N of Yucca Valley 3/13 1:15 am 34 18.7 118 26.4 2.6 2 mi. N of San Fernando 3/13 1:54 am 34 18.4 118 25.8 2.0 1 mi. NNE of San Fernando 3/13 1:55 am 34 18.6 118 32.5 2.2 4 mi. S of Newhall 3/13 3:12 am 34 14.2 118 36.4 2.7 2 mi. N of Canoga Park 3/13 3:35 am 33 13.3 115 33.4 2.1 2 mi. WSW of Niland 3/13 3:41 am 34 19.3 118 37.0 2.1 6 mi. ENE of Simi Valley 3/13 8:41 am 34 18.9 118 27.0 2.9 2 mi. NNW of San Fernando FELT 3/13 8:50 am 34 18.7 118 27.0 2.5 " 3/13 9:16 am 34 18.8 118 27.5 2.3 " 3/13 9:32 am 34 38.3 116 30.7 2.3 28 mi. ENE of Lucerne Valley 3/13 10:32 am 34 18.0 118 26.9 2.2 1 mi. NNW of San Fernando 3/13 12:23 pm 34 16.1 118 37.1 2.1 4 mi. N of Canoga Park 3/13 2:01 pm 34 18.8 118 25.0 2.0 2 mi. NNE of San Fernando 3/14 12:18 am 34 12.8 118 35.2 2.0 1 mi. NE of Canoga Park 3/14 2:02 am 34 14.0 118 36.8 2.2 2 mi. N of Canoga Park 3/14 2:58 am 34 15.1 118 29.1 2.4 2 mi. ENE of Northridge 3/14 3:14 am 34 26.5 116 31.7 2.0 22 mi. NNW of Yucca Valley 3/14 6:16 am 34 18.6 118 27.2 2.2 2 mi. NNW of San Fernando 3/14 2:22 pm 34 2.0 117 15.1 3.0 1 mi. SE of Loma Linda; FELT 3/14 5:13 pm 34 16.4 118 26.0 2.6 Under San Fernando 3/14 9:02 pm 34 23.0 116 27.7 2.2 18 mi. N of Yucca Valley 3/14 10:44 pm 34 19.4 118 34.1 2.2 4 mi. SSW of Newhall 3/15 1:37 am 34 18.7 118 36.8 2.1 5 mi. ENE of Simi Valley 3/15 2:44 am 34 19.6 118 28.4 3.0 3 mi. NNW of San Fernando 3/15 2:45 am 34 19.6 118 28.4 2.0 " 3/15 6:13 am 34 22.1 118 37.0 2.1 4 mi. SSW of Magic Mtn. 3/15 9:13 am 34 14.6 118 28.6 2.5 3 mi. SW of San Fernando FELT 3/15 11:26 am 34 23.1 116 27.8 2.0 18 mi. N of Yucca Valley 3/15 6:46 pm 34 18.0 118 26.6 2.0 1 mi. NNW of San Fernando 3/15 7:08 pm 34 22.0 118 43.0 2.2 6 mi. N of Simi Valley 3/15 9:16 pm 34 29.6 116 31.8 2.6 26 mi. N of Yucca Valley 3/15 9:41 pm 34 37.6 116 30.8 2.5 27 mi. ENE of Lucerne Valley 3/15 10:31 pm 34 14.2 116 25.5 2.1 8 mi. N of Yucca Valley 3/15 10:41 pm 34 37.9 116 33.7 2.1 25 mi. ENE of Lucerne Valley 3/16 3:46 am 35 2.7 116 58.9 2.0 11 mi. NNE of Barstow 3/16 3:51 am 34 17.3 118 25.1 2.0 1 mi. ENE of San Fernando 3/16 5:31 am 36 32.1 117 0.9 2.2 8 mi. ESE of Stovepipe Wells 3/16 7:49 am 34 22.4 118 41.5 3.0 6 mi. N of Simi Valley 3/16 8:50 am 34 23.0 116 27.5 2.0 18 mi. N of Yucca Valley 3/16 9:53 am 36 1.8 117 49.8 2.6 6 mi. E of Coso Junction 3/16 11:21 am 34 18.0 118 25.2 2.8 1 mi. NE of San Fernando 3/16 11:23 am 34 17.9 118 25.2 2.0 " 3/16 7:27 pm 34 0.9 117 7.3 2.1 4 mi. SE of Redlands 3/16 8:44 pm 34 23.6 118 37.7 2.1 3 mi. SW of Magic Mtn. 3/16 9:12 pm 34 23.6 118 37.6 2.4 " 3/16 10:07 pm 34 23.7 118 37.8 2.8 " FELT 3/16 11:54 pm 33 42.8 116 44.3 2.1 2 mi. SSW of Idyllwild ------------------------------------------------------------- Figure 1. A map of southern California showing the earthquakes recorded during the past week by the Caltech/USGS Seismic Network. Major faults are marked, as well as the metropolitan areas of Los Angeles (L.A.), Palm Springs (P.S.), San Diego (S.D.), and Santa Barbara (S.B.). The circles denote the earthquakes, the size of the circle indicating the magnitude.