February 17, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ February 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 Tuesday morning, February 10, Pacific Standard Time, to midnight Wednesday night, February 16, Pacific Standard Time. There are 627 this week. Not surprisingly, we had more aftershocks this week. The largest (M3.7) occurred in the Newhall area last Friday morning. Last week we said that we were statistically likely to have a M4 event and we didn't have it. That is the nature of statistical predictions, especially for small numbers of events. M3.7 is close. We had 9 of the 10 M3's that we expected, counting the event in the Santa Monica Mtns. on Tuesday night. These two "Westwood" events occurred above and slightly to the south of the main shock's rupture surface, near 8 km depth. They had strike-slip focal mechanisms. They, along with a group of small aftershocks near Calabasas in the last few weeks, appear to be part of the "hanging wall deformation". In thrust faulting earthquakes, one block (the "hanging wall") is pushed up and over the other block (the "foot wall"). We often see secondary faulting and aftershocks in the highly-stressed hanging wall. A M3.3 on Friday afternoon, located in Mexico, was felt in the El Centro region. A M3.2 the night before apparently escaped notice. This area has had similar activity several times over the last few months. The table lists the quakes that were M2.0 or larger in the central part of the coverage area. Aftershocks must be at least M2.5 to be listed. 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 ------------------------------------------------------------- 2/10 1:48 am 34 20.0 118 38.8 2.5 5 mi. NE of Simi Valley 2/10 2:00 am 33 30.5 116 27.8 2.0 12 mi. ESE of Anza 2/10 3:16 am 34 22.0 118 29.8 3.2 1 mi. ESE of Newhall; FELT 2/10 7:35 am 34 24.1 118 36.7 2.6 2 mi. SW of Magic Mtn. 2/10 8:34 am 34 19.4 116 27.2 2.1 14 mi. N of Yucca Valley 2/10 9:27 am 33 57.3 116 43.8 2.0 3 mi. NE of Cabazon 2/10 10:57 am 34 23.5 116 27.7 2.2 18 mi. N of Yucca Valley 2/10 12:16 pm 33 11.7 115 33.3 2.5 3 mi. SW of Niland 2/10 3:43 pm 34 28.0 116 31.5 2.0 24 mi. N of Yucca Valley 2/10 4:53 pm 34 22.2 118 30.5 3.1 1 mi. ESE of Newhall; FELT 2/10 4:55 pm 34 21.9 118 30.3 2.1 " 2/10 6:13 pm 33 50.1 116 46.4 2.3 6 mi. S of Cabazon 2/10 7:33 pm 34 15.0 118 27.7 2.3 2 mi. SSW of San Fernando 2/10 10:12 pm 32 26.0 115 24.0 3.2 17 mi. SSE of Calexico 2/10 10:41 pm 34 18.7 118 26.8 2.9 2 mi. NNW of San Fernando 2/11 1:03 am 34 57.6 116 56.8 2.2 6 mi. NE of Barstow 2/11 6:01 am 34 19.7 118 28.6 2.5 3 mi. NW of San Fernando 2/11 6:07 am 34 20.0 118 29.1 3.7 3 mi. SE of Newhall; FELT 2/11 6:23 am 34 21.7 118 34.5 2.5 2 mi. WSW of Newhall 2/11 7:52 am 34 24.0 118 46.5 3.0 9 mi. NNW of Simi Valley 2/11 12:20 pm 34 36.6 116 38.9 2.3 20 mi. NE of Lucerne Valley 2/11 3:25 pm 32 26.0 115 24.3 3.3 17 mi. SSE of Calexico; FELT 2/11 6:50 pm 34 16.6 118 34.1 2.5 3 mi. NW of Northridge 2/11 10:38 pm 32 38.7 117 24.2 2.8 13 mi. SW of San Diego 2/11 10:58 pm 34 19.4 118 36.2 2.5 5 mi. SW of Newhall 2/12 5:25 am 34 37.1 116 38.8 2.4 20 mi. NE of Lucerne Valley 2/12 5:39 am 33 4.8 117 50.4 2.1 27 mi. SSW of San Clemente 2/12 7:10 am 34 18.9 118 32.5 2.9 4 mi. S of Newhall 2/12 7:34 am 33 44.3 116 1.4 2.1 12 mi. NNE of Mecca 2/12 2:12 pm 34 17.4 118 32.1 2.6 3 mi. N of Northridge 2/12 4:43 pm 34 11.4 118 34.2 2.7 2 mi. ESE of Canoga Park 2/12 5:09 pm 34 11.8 118 33.2 2.5 2 mi. SSW of Northridge 2/13 3:56 am 34 16.7 118 26.1 2.7 Under San Fernando 2/13 7:22 am 32 48.5 116 6.1 2.5 8 mi. NW of Ocotillo 2/13 9:09 am 32 25.1 115 24.1 2.8 18 mi. SSE of Calexico 2/13 10:52 am 34 43.7 120 7.8 2.3 9 mi. N of Solvang 2/13 10:53 am 34 43.7 120 8.2 2.4 " 2/13 10:54 am 34 43.9 120 8.6 2.4 " 2/13 11:43 am 34 15.1 118 33.0 2.6 1 mi. NW of Northridge 2/13 1:21 pm 34 17.4 118 28.8 2.7 2 mi. WNW of San Fernando 2/13 2:09 pm 34 18.0 118 26.9 2.5 1 mi. NNW of San Fernando 2/13 3:29 pm 34 15.4 118 27.9 2.8 2 mi. SW of San Fernando 2/13 3:52 pm 34 19.8 118 26.2 2.5 3 mi. N of San Fernando 2/13 7:21 pm 34 17.3 118 28.7 2.7 2 mi. W of San Fernando 2/13 8:34 pm 34 16.6 118 34.4 2.5 3 mi. NW of Northridge 2/13 10:28 pm 36 12.8 118 11.0 2.3 11 mi. WSW of Olancha 2/13 10:33 pm 36 3.9 117 52.4 2.2 4 mi. ENE of Coso Junction 2/14 5:19 am 34 13.5 118 36.5 2.5 1 mi. N of Canoga Park 2/14 6:41 am 36 0.4 117 47.5 2.0 9 mi. ESE of Coso Junction 2/14 10:34 am 34 6.0 116 24.8 2.1 2 mi. SE of Yucca Valley 2/14 12:32 pm 34 12.4 118 33.3 3.3 2 mi. SSW of Northridge 2/14 4:22 pm 34 15.1 118 38.0 2.9 3 mi. NNW of Canoga Park 2/14 4:22 pm 34 15.3 118 38.9 2.8 3 mi. ESE of Simi Valley 2/14 4:23 pm 34 14.9 118 37.7 2.5 3 mi. NNW of Canoga Park 2/14 5:59 pm 34 13.9 118 36.9 2.5 2 mi. NNW of Canoga Park 2/14 6:53 pm 34 15.8 118 27.8 2.6 1 mi. SW of San Fernando 2/14 7:21 pm 32 7.2 116 22.6 3.1 48 mi. SSW of Ocotillo 2/14 9:39 pm 34 53.8 119 36.8 2.0 19 mi. SSW of Taft 2/14 9:55 pm 33 22.6 116 16.6 2.4 10 mi. NNE of Borrego Springs 2/14 10:28 pm 35 7.5 119 20.8 2.2 5 mi. ESE of Taft 2/15 12:50 am 35 55.8 117 56.7 2.3 8 mi. S of Coso Junction 2/15 1:42 am 34 22.3 118 38.5 3.1 4 mi. SW of Magic Mtn. 2/15 4:31 am 34 17.5 118 27.0 3.2 1 mi. NW of San Fernando FELT 2/15 5:51 am 34 14.4 118 33.7 2.9 1 mi. W of Northridge; FELT 2/15 6:54 am 34 26.2 116 30.8 2.1 22 mi. N of Yucca Valley 2/15 11:21 am 35 55.8 120 27.9 2.8 2 mi. NW of Parkfield 2/15 12:09 pm 34 18.4 118 30.0 2.8 3 mi. WNW of San Fernando 2/15 11:58 pm 34 5.8 118 30.6 3.2 4 mi. NW of Westwood Village FELT 2/16 12:02 am 34 5.5 118 30.5 2.5 " 2/16 10:00 am 34 17.2 118 26.7 3.1 Under San Fernando; FELT 2/16 11:17 am 34 0.7 116 18.9 2.4 10 mi. SE of Yucca Valley 2/16 11:23 am 33 54.4 116 16.5 2.0 13 mi. NNW of Indio 2/16 1:57 pm 34 21.1 118 41.7 2.5 5 mi. N of Simi Valley 2/16 6:41 pm 32 26.4 115 24.4 2.6 16 mi. SSE of Calexico 2/16 7:03 pm 34 21.3 116 27.4 2.0 16 mi. N of Yucca Valley 2/16 9:19 pm 34 13.8 116 45.2 2.0 6 mi. ESE of Big Bear City 2/16 11:21 pm 34 18.9 118 33.7 2.7 4 mi. SSW of Newhall ------------------------------------------------------------- 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.