February 3, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ January 27 - February 2, 1994 Prepared by: Kate Hutton, Seismological Laboratory (kate@bombay.gps.caltech.edu) Egill Hauksson, Seismological Laboratory 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, January 27, Pacific Standard Time, to midnight Wednesday night, February 2, Pacific Standard Time. There are 759 this week, and the list is by no means complete since we are still behind in the data processing. Northridge aftershocks continue to dominate seismicity. Several were above M4 and widely felt; these are noted in the table. The M5.0 that occurred early Saturday morning was shallow, at a depth of about 1 km, and had a strike-slip focal mechanism. This is unlike the Northridge main shock and most of the aftershocks, which had thrust mechanisms. We do not know what fault caused the M5.0, but we know it was not the one that caused the main shock. Aside from the usual crop of spurious rumors involving nonexistant earthquake predictions, the "flap" of the week was location of the mainshock epicenter, actually in the Reseda zip code rather than the Northridge zip code, and the name of the earthquake. Our comment on this is that we (meaning scientists) name earthquakes for convenience if referring to them, and no other reason. Furthermore, the hypocenter, or the spot at 18 km. depth under the epicenter, is only the place where the rupture started. During the earthquake, it spread upward and to the north, as well as both east and west, under many communities. Northridge happened to be right in the middle of all this, so Northridge still seems like an appropriate name for the earthquake. The seismicity elsewhere in the region still looks lower than it has been. We believe this is not real, but rather an artifact of the preliminary data processing that we are currently doing. Since we look at only one event per trigger of the on-line system and are concentrating on aftershocks, we expect many small quakes elsewhere to stay hidden in the data until we can do a more thorough job. The table lists the quakes that were M2.0 or larger in the central part of the coverage area. The data processing is still incomplete due to the huge number of Northridge events. 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 ------------------------------------------------------------- 1/27 2:34 am 34 21.7 118 27.7 2.5 3 mi. ESE of Newhall 1/27 4:10 am 34 19.2 118 27.9 2.6 3 mi. NNW of San Fernando 1/27 4:13 am 33 8.4 116 23.6 2.0 8 mi. S of Borrego Springs 1/27 5:49 am 34 21.7 118 28.8 2.6 2 mi. ESE of Newhall 1/27 6:31 am 34 15.0 118 35.3 3.2 3 mi. NNE of Canoga Park 1/27 7:05 am 33 24.8 116 38.9 2.0 9 mi. S of Anza 1/27 8:22 am 34 14.7 118 38.2 2.5 3 mi. NNW of Canoga Park 1/27 9:19 am 34 16.3 118 33.8 4.5 2 mi. NW of Northridge WIDELY FELT 1/27 9:56 am 34 10.7 118 37.3 2.7 1 mi. SSW of Canoga Park 1/27 10:57 am 34 24.3 116 30.5 3.3 20 mi. N of Yucca Valley 1/27 12:41 pm 34 21.3 118 33.1 3.0 2 mi. SW of Newhall 1/27 1:29 pm 34 14.9 118 29.1 2.6 2 mi. ENE of Northridge 1/27 2:14 pm 34 24.5 116 30.6 2.2 20 mi. N of Yucca Valley 1/27 3:03 pm 34 21.2 118 37.0 2.5 5 mi. SSW of Magic Mtn. 1/27 3:24 pm 33 8.2 116 5.9 2.0 1 mi. ESE of Ocotillo Wells 1/27 6:49 pm 35 46.6 120 21.1 2.8 4 mi. NW of Cholame 1/27 8:58 pm 34 18.6 118 27.6 3.3 2 mi. NNW of San Fernando 1/27 9:24 pm 34 32.2 116 32.7 2.2 23 mi. ENE of Lucerne Valley 1/27 9:47 pm 34 21.4 118 37.8 3.2 5 mi. SSW of Magic Mtn. 1/27 10:06 pm 34 18.0 118 27.0 2.5 1 mi. NNW of San Fernando 1/27 10:26 pm 35 2.1 116 58.8 2.0 10 mi. NNE of Barstow 1/27 10:42 pm 34 22.1 118 30.6 2.5 1 mi. SE of Newhall 1/27 10:46 pm 34 24.5 116 30.5 2.1 20 mi. N of Yucca Valley 1/27 11:44 pm 34 13.9 118 36.8 3.4 2 mi. NNW of Canoga Park 1/28 2:24 am 34 24.5 116 30.6 2.3 20 mi. N of Yucca Valley 1/28 4:34 am 34 22.2 118 29.5 2.6 2 mi. ESE of Newhall 1/28 4:48 am 34 22.2 118 29.5 3.2 " 1/28 7:14 am 33 33.5 116 44.8 2.1 4 mi. W of Anza 1/28 11:05 am 36 13.8 120 48.9 2.8 26 mi. WNW of Coalinga 1/28 11:36 am 33 40.6 116 47.1 2.3 6 mi. SW of Idyllwild 1/28 12:09 pm 34 22.5 118 29.7 4.0 1 mi. E of Newhall WIDELY FELT 1/28 12:11 pm 34 22.5 118 30.1 3.5 " 1/28 3:04 pm 34 21.6 118 29.1 2.6 2 mi. ESE of Newhall 1/28 4:47 pm 34 17.3 118 27.6 2.9 1 mi. WNW of San Fernando 1/28 7:21 pm 33 39.1 116 42.8 3.1 6 mi. S of Idyllwild 1/28 9:18 pm 33 39.8 119 4.1 2.2 13 mi. N of Santa Barbara Is. 1/28 11:52 pm 34 13.8 118 36.8 2.6 2 mi. NNW of Canoga Park 1/29 2:42 am 34 18.8 118 28.0 2.8 2 mi. NW of San Fernando 1/29 3:13 am 34 18.3 118 24.8 3.5 2 mi. NE of San Fernando 1/29 3:20 am 34 18.3 118 34.8 5.0 5 mi. NNW of Northridge WIDELY FELT, FURTHER DAMAGE 1/29 3:23 am 34 18.6 118 34.3 3.0 5 mi. SSW of Newhall 1/29 3:25 am 34 14.5 118 34.1 2.7 2 mi. W of Northridge 1/29 3:25 am 34 19.1 118 35.9 2.5 5 mi. SW of Newhall 1/29 3:37 am 34 24.0 118 36.7 3.4 2 mi. SW of Magic Mtn. 1/29 4:16 am 34 16.6 118 36.7 4.2 5 mi. N of Canoga Park WIDELY FELT 1/29 4:21 am 34 17.6 118 36.4 3.3 5 mi. NW of Northridge 1/29 4:35 am 34 18.7 118 33.7 2.9 5 mi. SSW of Newhall 1/29 4:47 am 34 20.9 118 36.6 3.2 5 mi. SSW of Magic Mtn. 1/29 4:59 am 34 18.7 118 33.7 3.1 5 mi. SSW of Newhall 1/29 5:15 am 34 17.1 118 37.8 2.8 4 mi. E of Simi Valley 1/29 6:03 am 34 17.9 118 34.0 3.4 4 mi. NNW of Northridge 1/29 6:03 am 34 17.8 118 33.9 2.9 " 1/29 6:04 am 34 17.5 118 34.0 2.7 " 1/29 7:00 am 34 38.5 116 39.3 3.1 21 mi. NE of Lucerne Valley 1/29 7:10 am 34 17.9 118 35.1 2.5 5 mi. NW of Northridge 1/29 8:19 am 34 11.0 118 37.3 2.8 1 mi. SW of Canoga Park 1/29 9:22 am 34 17.8 118 34.0 2.6 4 mi. NNW of Northridge 1/29 10:20 am 34 17.6 118 37.9 2.8 4 mi. ENE of Simi Valley 1/29 10:54 am 34 23.7 118 37.4 2.6 2 mi. SW of Magic Mtn. 1/29 11:25 am 34 22.5 118 39.2 2.8 4 mi. SW of Magic Mtn. 1/29 1:08 pm 34 16.4 118 36.8 2.5 5 mi. N of Canoga Park 1/29 1:45 pm 34 18.7 118 28.4 3.1 2 mi. NW of San Fernando 1/29 2:49 pm 35 16.2 117 37.1 2.0 24 mi. S of Ridgecrest 1/29 4:12 pm 34 16.2 118 27.9 2.8 1 mi. WSW of San Fernando 1/29 4:50 pm 34 16.2 118 27.9 2.6 " 1/29 7:03 pm 34 19.2 118 31.5 2.6 4 mi. S of Newhall 1/29 8:22 pm 34 57.7 116 33.6 3.2 26 mi. E of Barstow 1/29 8:59 pm 34 15.2 118 28.0 2.8 2 mi. SW of San Fernando 1/29 10:35 pm 34 21.9 118 33.7 2.7 2 mi. WSW of Newhall 1/30 12:19 am 34 16.8 118 28.9 3.0 2 mi. W of San Fernando 1/30 1:19 am 34 18.9 118 33.3 3.3 4 mi. SSW of Newhall 1/30 2:44 am 34 22.6 118 34.0 3.2 2 mi. W of Newhall 1/30 2:54 am 34 19.3 118 30.8 2.6 4 mi. S of Newhall 1/30 5:22 am 34 20.1 118 32.3 2.6 3 mi. SSW of Newhall 1/30 7:42 am 34 22.0 118 43.0 2.5 6 mi. N of Simi Valley 1/30 9:01 am 34 18.4 118 26.7 2.8 1 mi. NNW of San Fernando 1/30 3:22 pm 34 19.8 118 36.9 2.5 6 mi. SSW of Magic Mtn. 1/30 8:27 pm 34 22.5 118 31.3 2.5 Under Newhall 1/30 8:55 pm 34 17.6 118 37.3 3.3 5 mi. ENE of Simi Valley 1/30 9:20 pm 34 17.3 118 37.1 2.9 6 mi. N of Canoga Park 1/31 1:22 am 33 24.7 116 38.8 2.0 9 mi. S of Anza 1/31 1:35 am 34 19.3 118 31.2 2.6 3 mi. S of Newhall 1/31 2:29 am 33 55.4 119 2.8 2.0 10 mi. SW of Leo Carrillo State Beach 1/31 3:41 am 34 17.4 118 25.6 2.8 Under San Fernando 1/31 5:46 am 34 20.8 118 31.3 2.5 2 mi. S of Newhall 1/31 9:38 am 34 19.5 118 36.8 2.5 6 mi. SSW of Magic Mtn. 1/31 5:55 pm 34 10.7 116 26.2 2.0 4 mi. N of Yucca Valley 1/31 10:08 pm 34 13.4 118 35.6 3.0 1 mi. NNE of Canoga Park 1/31 11:40 pm 34 13.9 118 37.4 3.6 2 mi. NNW of Canoga Park 2/1 1:29 am 34 9.1 119 10.4 2.7 1 mi. ENE of Port Hueneme 2/1 1:59 am 34 19.7 118 41.8 3.2 3 mi. NNE of Simi Valley 2/1 4:51 am 34 18.9 118 30.2 2.6 4 mi. SSE of Newhall 2/1 9:15 am 34 14.1 118 27.7 2.5 3 mi. SSW of San Fernando 2/1 10:23 am 34 20.1 118 36.9 2.9 6 mi. SSW of Magic Mtn. 2/1 1:15 pm 34 15.0 118 37.4 2.7 3 mi. NNW of Canoga Park 2/1 4:01 pm 34 23.3 116 27.6 2.8 18 mi. N of Yucca Valley 2/1 5:26 pm 34 19.0 118 27.6 2.7 2 mi. NNW of San Fernando 2/1 5:58 pm 34 24.6 119 18.1 2.3 3 mi. SW of Ojai 2/1 7:13 pm 33 56.3 117 3.6 2.7 4 mi. W of Beaumont 2/1 9:16 pm 35 46.3 116 35.4 2.1 22 mi. SW of Shoshone 2/1 11:30 pm 34 19.1 118 27.6 2.7 2 mi. NNW of San Fernando 2/1 11:31 pm 32 11.2 117 40.0 2.5 44 mi. SW of San Ysidro 2/2 3:24 am 34 17.5 118 36.6 3.7 6 mi. N of Canoga Park 2/2 3:51 am 34 22.4 118 31.0 3.0 Under Newhall 2/2 7:11 am 34 26.5 116 29.2 3.2 22 mi. N of Yucca Valley 2/2 7:12 am 36 13.2 120 11.5 2.6 10 mi. ENE of Coalinga 2/2 7:55 am 34 23.4 118 34.8 2.8 2 mi. S of Magic Mtn. 2/2 11:52 am 34 18.5 118 26.0 2.6 1 mi. N of San Fernando 2/2 6:24 pm 34 16.3 118 34.8 2.5 3 mi. NW of Northridge 2/2 11:03 pm 33 38.3 117 10.4 2.3 13 mi. WSW of Hemet; FELT 2/3 12:21 am 34 18.3 118 26.1 3.0 1 mi. N of San Fernando ------------------------------------------------------------- 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.