July 28, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ July 21 - 27, 1994 Prepared by: Debbie Wells, Seismological Laboratory Nick Scheckel, 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, July 21, Pacific Daylight Time, to midnight Wednesday night, July 27, Pacific Daylight Time. We recorded 433 earthquakes this week. The most noteworthy activity of the week was the continuing swarm in the Fontana area. The largest of these events was a M3.5 that occurred on Tuesday evening and was widely felt in the Inland Empire. Three other events were felt in this area on Wednesday. There was a M2.5 in the morning, followed by a M2.9 and a M2.7 that night. Further details of this swarm are provided in the attached supplement. For e-mail users, the supplement will be posted separ- ately. The largest event of the week occurred on Monday, a M3.7, in the area of Trona, northeast of Ridgecrest, in the Mojave Desert. As this is a sparsely populated area, it went unfelt by the general public, although there was some interest from the media. There were plenty of people in Marina del Rey, on the other hand, who felt the M2.7 that occurred there on Thursday afternoon. Activity is continuing in the Baker area, with a M3.1 on Friday as its largest event of the week. We had no reports of these events being felt. Landers and Northridge aftershocks are continu- ing as expected. 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 7 hrs, to the Daylight Time listed. Table 1 ------- Date Time N Lat. W Long. Mag ------------------------------------------------------------- 7/21 1:59 am 34 4.6 116 43.1 2.2 6 mi. ESE of Mt. San Gorgonio 7/21 7:02 am 36 9.4 117 51.3 2.6 5 mi. ENE of south end of Haiwee Reservoir 7/21 7:19 am 34 2.3 116 35.9 2.3 7 mi. NW of Desert Hot Springs 7/21 11:39 am 32 40.2 115 54.6 2.3 6 mi. SE of Ocotillo 7/21 1:17 pm 34 23.1 116 27.6 2.1 18 mi. N of Yucca Valley 7/21 1:41 pm 35 3.3 118 18.8 2.1 8 mi. W of Mojave 7/21 2:29 pm 35 6.4 118 22.0 2.0 4 mi. ESE of Tehachapi 7/21 3:57 pm 33 58.4 118 26.3 2.7 Under Marina del Rey; FELT 7/22 3:20 am 34 37.6 116 39.5 2.5 20 mi. NE of Lucerne Valley 7/22 6:22 am 33 51.9 116 53.0 2.3 4 mi. S of Banning 7/22 8:14 am 35 21.9 118 30.8 2.1 16 mi. NNW of Tehachapi 7/22 7:00 pm 35 56.8 117 18.6 2.1 12 mi. NNE of Trona 7/22 10:12 pm 34 47.5 116 17.6 3.1 35 mi. SSW of Baker 7/22 10:24 pm 34 47.2 116 17.5 2.4 35 mi. SSW of Baker 7/22 10:41 pm 34 20.9 119 32.4 2.5 3 mi. SSW of Carpinteria 7/22 10:50 pm 34 14.0 118 45.0 2.0 3 mi. SW of Simi Valley 7/23 4:29 am 34 17.6 118 27.7 2.7 1 mi. WNW of San Fernando 7/23 5:24 am 34 14.2 118 27.9 2.5 3 mi. SSW of San Fernando 7/23 5:42 am 34 19.3 118 18.2 2.2 9 mi. NNE of Burbank Airport 7/23 7:15 am 34 14.1 118 28.3 2.0 3 mi. SSW of San Fernando 7/23 4:16 pm 34 14.2 118 27.6 2.3 3 mi. SSW of San Fernando 7/23 6:30 pm 36 0.6 117 49.0 2.1 7 mi. ESE of Coso Junction 7/23 6:51 pm 32 5.5 117 5.7 2.1 31 mi. S of San Ysidro 7/24 3:54 am 35 32.2 120 11.1 2.0 14 mi. SSE of Cholame 7/24 4:44 am 33 46.6 116 9.4 2.1 5 mi. NE of Indio 7/24 6:34 am 34 3.2 117 30.5 2.6 5 mi. SW of Fontana 7/24 8:20 am 33 57.8 116 40.2 2.9 7 mi. ENE of dinosaurs, Cabazon 7/24 2:42 pm 34 23.0 116 27.3 2.2 18 mi. N of Yucca Valley 7/24 7:11 pm 33 57.8 116 40.3 2.2 7 mi. ENE of dinosaurs, Cabazon 7/24 7:53 pm 34 14.9 118 27.0 2.0 2 mi. SSW of San Fernando 7/25 9:18 am 34 2.8 117 30.7 2.4 6 mi. SW of Fontana 7/25 9:36 am 34 19.1 118 34.1 2.0 4 mi. SSW of Newhall 7/25 10:00 am 34 2.9 117 30.6 2.2 5 mi. SW of Fontana 7/25 12:20 pm 33 15.0 116 16.8 2.2 5 mi. E of Borrego Springs 7/25 12:33 pm 35 0.8 116 50.3 2.2 13 mi. NE of Barstow 7/25 12:40 pm 33 46.1 116 9.1 2.0 5 mi. NE of Indio 7/25 1:48 pm 34 3.6 117 16.4 2.3 5 mi. SW of Fontana 7/25 4:11 pm 34 2.4 116 18.3 2.0 9 mi. SE of Yucca Valley 7/25 4:18 pm 35 44.5 117 3.2 3.7 17 mi. E of Trona 7/25 4:35 pm 34 12.9 116 26.3 2.5 6 mi. N of Yucca Valley 7/25 6:48 pm 32 40.1 115 54.6 2.3 6 mi. SE of Ocotillo 7/25 7:58 pm 34 13.9 118 36.2 2.5 2 mi. N of Canoga Park 7/25 8:56 pm 34 59.6 117 2.5 2.0 7 mi. N of Barstow 7/26 12:34 am 34 2.9 117 30.6 2.1 5 mi. SW of Fontana 7/26 8:10 am 34 2.9 117 30.5 2.0 " 7/26 8:41 am 36 25.9 121 2.3 2.6 35 mi. SE of Hollister 7/26 12:22 pm 34 18.2 118 23.9 2.4 2 mi. ENE of San Fernando 7/26 12:22 pm 35 58.2 118 21.0 2.4 23 mi. NNE of the town of Lake Isabella 7/26 2:28 pm 34 2.7 117 30.4 2.0 6 mi. SW of Fontana 7/26 2:40 pm 34 2.7 117 30.4 2.1 " 7/26 3:28 pm 34 2.9 117 30.4 2.0 5 mi. SW of Fontana 7/26 7:24 pm 34 3.1 117 30.8 3.5 5 mi. SW of Fontana; FELT 7/26 7:37 pm 34 3.2 117 30.8 2.5 " 7/26 9:14 pm 33 58.5 116 21.7 2.2 8 mi. E of Desert Hot Springs 7/26 10:32 pm 34 13.9 118 43.3 2.0 3 mi. SSW of Simi Valley 7/27 9:01 am 34 3.1 117 30.8 2.5 5 mi. SW of Fontana; FELT 7/27 12:45 pm 34 47.0 116 17.7 2.0 35 mi. SSW of Baker 7/27 1:03 pm 35 2.0 117 0.1 2.0 10 mi. N of Barstow 7/27 1:49 pm 34 2.5 117 30.4 2.0 6 mi. SW of Fontana 7/27 7:43 pm 35 12.3 120 58.4 2.4 13 mi. SSW of Morro Bay 7/27 8:17 pm 34 16.8 118 29.5 2.0 2 mi. W of San Fernando 7/27 9:31 pm 34 2.8 117 30.7 2.9 6 mi. SW of Fontana; FELT 7/27 11:11 pm 34 2.7 117 30.4 2.1 " 7/27 11:11 pm 34 2.9 117 30.3 2.1 5 mi. SW of Fontana 7/27 11:44 pm 34 2.6 117 30.5 2.7 6 mi. SW of Fontana; FELT ------------------------------------------------------------- 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.