April 7, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ March 31 - April 6, 1994 Prepared by: Kate Hutton, Seismological Laboratory (kate@bombay.gps.caltech.edu) Nick Scheckel 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 31, Pacific Standard Time, to midnight Wednesday night, April 6, Pacific Daylight Time. There are 499 this week. Although the total number of events this week was not unusual, compared to recent activity, a somewhat larger percentage of them were felt. The strongest was the M4.8 that occurred slightly after noon on Wedneday, near Lake Arrowhead. It was felt at least as far away as the Seismological Society of America meeting in Pasadena. It occurred just west of the aftershocks generated by the Big Bear earthquake in '92, with a focal mechanism that showed oblique thrust; in other words, a combination of thrust and strike-slip. Very early in the morning on the same day, a smaller Landers aftershock (M3.8) woke sleepers in Yucca Valley. It occurred in a remote area north of Yucca Valley. Several Northridge aftershocks were felt this week also. These included a M3.3 on Saturday morning, a M2.6 just before noon on Sunday, and a M3.5, followed by a M2.6, on Wednesday evening. The aftershock decay curve is still predicting 2 or 3 aftershocks above M3 per week, right in line with what actually happened. There were also three "miscellaneous" felt quakes, not in or near current aftershock sequences. On Tuesday morning, a M3.1 was felt in the Redlands area. Regular readers of this report know that Redlands is very active with small quakes. On Sunday evening, a M3.2 occurred in the Mt. Palomar area in San Diego County. It was felt in the Desert Hot Springs area. A small quake (M2.7) in the Monterey Park area attracted some attention last Thursday morning, since it was felt in the Seismological Laboratory. It occurred in what was the aftershock zone of the Whittier Narrows quake, but after several years of quiet, it is probably not an aftershock. The second and third largest events on the map (M4.4 and M4.2) occurred near Coalinga last Thursday. For more information about these, contact the U.S. Geological Survey in Menlo Park, at 415-853-8300. 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 (or 7 hrs to the Pacific Daylight Time, as appropriate). Table 1 ------- Date Time N Lat. W Long. Mag ------------------------------------------------------------- 3/31 2:48 am 34 20.5 118 28.9 2.1 3 mi. SE of Newhall 3/31 3:36 am 34 16.1 118 37.1 2.3 4 mi. N of Canoga Park 3/31 7:13 am 34 27.7 119 5.0 2.3 9 mi. E of Ojai 3/31 7:48 am 34 3.1 118 7.3 2.7 1 mi. NE of Monterey Park FELT 3/31 9:58 am 34 21.9 118 37.5 2.0 4 mi. SSW of Magic Mtn. 3/31 11:25 am 34 15.4 118 28.6 2.1 2 mi. SW of San Fernando 3/31 12:00 pm 36 10.9 120 13.1 4.4 8 mi. ENE of Coalinga 3/31 12:02 pm 36 11.2 120 13.1 4.2 8 mi. ENE of Coalinga 3/31 12:27 pm 34 15.2 118 27.8 2.2 2 mi. SW of San Fernando 3/31 2:54 pm 34 16.9 118 29.1 2.1 2 mi. W of San Fernando 3/31 4:10 pm 33 35.6 118 19.5 2.2 7 mi. SSW of Pt. Fermin, San Pedro 3/31 10:09 pm 34 16.7 118 28.1 2.0 1 mi. W of San Fernando 3/31 11:15 pm 33 14.2 115 40.4 2.2 8 mi. SSE of Bombay Beach 3/31 11:26 pm 35 48.4 120 27.2 2.0 6 mi. S of Parkfield 4/1 12:30 am 34 22.6 116 28.0 2.2 17 mi. N of Yucca Valley 4/1 1:07 am 34 17.1 118 37.5 2.7 4 mi. E of Simi Valley 4/1 1:07 am 34 16.9 118 37.9 2.0 4 mi. E of Simi Valley 4/1 1:08 am 34 17.2 118 37.5 2.1 4 mi. E of Simi Valley 4/1 2:36 am 34 12.6 116 46.8 2.6 5 mi. SE of Big Bear City 4/1 7:02 am 34 18.9 118 27.0 2.1 2 mi. NNW of San Fernando 4/1 12:28 pm 36 13.6 120 14.8 2.5 8 mi. NE of Coalinga 4/1 12:48 pm 34 21.1 118 37.1 2.0 5 mi. SSW of Magic Mtn. 4/1 3:26 pm 32 29.5 115 14.9 2.5 18 mi. SE of Calexico 4/1 8:46 pm 34 18.3 118 26.8 2.0 1 mi. NNW of San Fernando 4/1 9:53 pm 34 16.9 118 29.9 2.0 3 mi. NNE of Northridge 4/1 10:03 pm 33 10.2 116 2.8 2.1 5 mi. ENE of Ocotillo Wells 4/2 12:54 am 34 38.1 116 35.0 2.0 24 mi. ENE of Lucerne Valley 4/2 4:18 am 34 17.9 118 27.8 2.0 1 mi. NW of San Fernando 4/2 6:10 am 34 22.0 118 39.3 3.3 5 mi. SW of Magic Mtn. FELT 4/2 6:25 am 34 21.4 116 28.0 2.3 16 mi. N of Yucca Valley 4/2 6:53 am 34 9.8 116 25.3 2.2 3 mi. NNE of Yucca Valley 4/2 7:06 am 34 21.9 118 38.4 2.0 5 mi. SW of Magic Mtn. 4/2 10:14 am 34 21.5 118 38.0 2.2 5 mi. SSW of Magic Mtn. 4/2 11:48 am 34 10.8 116 49.6 2.2 5 mi. N of Mt. San Gorgonio 4/2 2:13 pm 34 9.4 116 51.1 2.0 4 mi. NNW of Mt. San Gorgonio 4/2 2:37 pm 34 55.7 120 34.2 2.0 7 mi. WSW of Santa Maria 4/2 3:48 pm 33 57.9 116 33.4 2.2 3 mi. W of Desert Hot Springs 4/2 8:41 pm 34 22.6 118 34.6 2.5 3 mi. SSE of Magic Mtn. 4/3 1:09 am 34 19.6 118 35.7 2.6 5 mi. SW of Newhall 4/3 3:32 am 34 24.3 116 27.8 2.3 19 mi. N of Yucca Valley 4/3 5:06 am 34 19.4 118 36.3 2.3 5 mi. SW of Newhall 4/3 7:41 am 34 15.8 116 27.2 2.2 10 mi. N of Yucca Valley 4/3 11:28 am 34 13.4 118 35.6 2.6 1 mi. NNE of Canoga Park FELT 4/3 12:21 pm 34 34.9 116 36.8 2.0 21 mi. ENE of Lucerne Valley 4/3 1:25 pm 34 12.9 116 44.6 2.0 7 mi. ESE of Big Bear City 4/3 2:54 pm 34 9.4 118 43.7 2.0 6 mi. E of Thousand Oaks 4/3 4:18 pm 34 11.8 118 38.0 2.2 1 mi. W of Canoga Park 4/3 5:48 pm 33 14.5 115 39.8 2.0 8 mi. SSE of Bombay Beach 4/3 8:25 pm 33 26.5 116 51.2 3.2 5 mi. N of Palomar Observatory; FELT 4/3 10:19 pm 34 18.4 118 25.0 2.2 2 mi. NE of San Fernando 4/3 10:27 pm 36 12.8 120 13.0 2.4 9 mi. ENE of Coalinga 4/3 12:53 am 35 8.0 120 56.3 2.0 16 mi. SSW of Morro Bay 4/4 3:06 am 34 18.5 118 25.1 2.4 2 mi. NNE of San Fernando 4/4 5:10 am 34 9.4 116 25.9 2.0 2 mi. NNE of Yucca Valley 4/4 6:28 am 33 21.3 116 18.7 2.5 7 mi. NNE of Borrego Springs 4/4 9:46 am 35 45.8 118 25.1 2.0 9 mi. NNE of the town of Lake Isabella 4/4 10:30 am 34 45.5 120 57.3 2.5 21 mi. NW of Pt. Arguello 4/4 5:00 pm 35 14.3 116 43.5 2.4 12 mi. SE of Goldstone (dry) Lake 4/4 7:09 pm 34 12.7 118 38.8 2.1 2 mi. WNW of Canoga Park 4/4 9:59 pm 34 22.0 118 36.8 2.2 4 mi. SSW of Magic Mtn. 4/4 10:47 pm 34 13.1 118 30.8 2.0 1 mi. SE of Northridge 4/5 1:15 pm 34 20.5 118 34.4 2.0 3 mi. SW of Newhall 4/5 2:25 am 34 33.6 116 35.4 2.3 21 mi. ENE of Lucerne Valley 4/5 7:14 am 33 39.2 119 4.8 2.1 12 mi. N of Santa Barbara Is 4/5 8:05 am 34 55.3 116 45.9 2.2 14 mi. E of Barstow 4/5 8:17 am 34 0.7 117 6.3 3.1 5 mi. SE of Redlands; FELT 4/5 8:47 am 34 15.9 118 28.3 2.1 2 mi. WSW of San Fernando 4/5 9:52 am 34 20.8 118 27.6 2.0 4 mi. NNW of San Fernando 4/5 3:15 pm 34 17.7 118 24.6 2.2 1 mi. ENE of San Fernando 4/5 3:22 pm 34 14.3 118 45.2 2.1 3 mi. SW of Simi Valley 4/5 4:26 pm 34 22.7 118 37.4 2.2 3 mi. SSW of Magic Mtn. 4/5 4:49 pm 34 22.6 118 37.2 2.7 3 mi. SSW of Magic Mtn. 4/5 12:26 am 34 28.6 116 30.9 3.8 25 mi. N of Yucca Valley FELT 4/5 12:27 am 34 28.6 116 31.2 2.9 25 mi. N of Yucca Valley 4/6 2:18 am 34 21.0 118 32.0 3.0 2 mi. S of Newhall 4/6 3:35 am 36 35.2 117 6.3 2.0 2 mi. ESE of Stovepipe Wells 4/6 3:51 am 34 14.1 118 29.0 2.0 2 mi. E of Northridge 4/6 6:39 am 35 14.9 120 47.7 2.5 8 mi. SSE of Morro Bay 4/6 8:22 am 34 10.7 116 26.2 2.2 4 mi. N of Yucca Valley 4/6 12:01 pm 34 11.5 117 5.7 4.8 1 mi. SSE of Running Springs; WIDELY FELT 4/6 2:26 pm 34 11.6 117 5.9 2.2 " 4/6 8:56 pm 34 20.9 118 33.7 2.1 2 mi. SW of Newhall 4/6 9:19 pm 34 20.0 118 27.9 3.5 3 mi. NNW of San Fernando FELT 4/6 9:40 pm 34 20.0 118 28.0 2.6 3 mi. NNW of San Fernando FELT 4/6 11:31 pm 34 14.4 118 28.6 2.0 3 mi. SW 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.