August 11, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ August 4 - 10, 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, August 4, Pacific Daylight Time, to midnight Wednesday night, August 10, Pacific Daylight Time. We recorded 325 earthquakes this week. The largest quake of the week occurred yesterday evening (Wednesday), but it occurred in northern Baja. Preliminary magnitude was M4.5. We didn't get any reports that it was felt in the U.S., but it was large enough and close enough to Imperial Valley to be felt there. The second largest event was a M4.0 Landers aftershock on Sunday morning, near the southern end of the Landers rupture. It and two of its aftershocks, during the afternoon and evening of the same day, were felt. The M4.0 had the usual Landers strike-slip focal mechanism. In case you've forgotten, the Landers earthquake was a Mw7.3 and occurred on June 28, 1992. The largest Northridge aftershock of the week was a M2.8, early Sunday morning, on the eastern end of the aftershock zone. The Northridge quake was Mw6.7 and occurred on January 17, 1994. The Fontana cluster continued at a much lower level this week, the largest one being a M2.7 on Saturday. 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 ------------------------------------------------------------- 8/4 5:55 am 33 21.5 116 22.5 2.3 7 mi. N of Borrego Springs 8/4 6:23 am 34 15.1 118 28.3 2.0 2 mi. SW of San Fernando 8/4 10:29 am 34 59.2 116 57.1 2.2 7 mi. NNE of Barstow 8/4 10:39 am 34 38.0 116 31.6 2.1 27 mi. ENE of Lucerne Valley 8/4 12:13 pm 34 19.6 118 28.7 2.1 3 mi. NW of San Fernando 8/4 5:31 pm 34 16.6 118 28.2 2.0 1 mi. W of San Fernando 8/5 1:56 am 32 41.0 115 55.3 2.4 5 mi. SE of Ocotillo 8/5 3:12 am 34 20.0 116 28.1 2.4 14 mi. N of Yucca Valley 8/5 10:24 am 34 37.7 116 30.3 2.1 28 mi. ENE of Lucerne Valley 8/5 5:41 pm 34 16.2 118 25.2 2.3 1 mi. SE of San Fernando 8/5 11:40 pm 34 22.3 116 28.0 2.3 17 mi. N of Yucca Valley 8/6 11:05 am 34 3.3 117 30.9 2.7 Fontana, 1 mi. ESE of the I10/I15 interchange; FELT 8/6 7:43 pm 33 47.1 117 13.3 2.1 16 mi. SSE of downtown Riverside 8/6 8:18 pm 34 15.4 118 27.9 2.6 2 mi. SW of San Fernando 8/6 10:35 pm 33 11.5 115 36.3 2.3 Obsidian Butte, 5 mi. WSW of Niland 8/6 11:38 pm 34 23.5 116 27.8 2.3 18 mi. N of Yucca Valley 8/7 1:33 am 34 18.2 118 25.1 2.5 1 mi. NE of San Fernando 8/7 3:56 am 34 16.2 118 27.6 2.8 1 mi. SW of San Fernando 8/7 4:33 am 34 28.6 116 30.3 2.4 25 mi. N of Yucca Valley 8/7 8:10 am 33 59.5 116 16.5 4.0 13 mi. SE of Yucca Valley FELT 8/7 8:34 am 33 59.6 116 16.3 2.5 " 8/7 8:35 am 34 38.2 116 30.9 2.1 27 mi. ENE of Lucerne Valley 8/7 10:25 am 36 52.9 118 15.9 2.2 6 mi. NW of Independence 8/7 4:43 pm 33 59.5 116 16.5 3.6 13 mi. SE of Yucca Valley FELT 8/7 8:52 pm 33 59.4 116 16.3 2.8 13 mi. SE of Yucca Valley FELT 8/8 2:28 am 34 20.8 118 33.9 2.5 3 mi. SW of Newhall 8/8 6:39 am 34 13.9 116 26.8 2.4 7 mi. N of Yucca Valley 8/8 8:07 am 33 42.2 116 45.6 2.1 3 mi. SW of Idyllwild 8/8 2:19 pm 34 14.9 118 27.4 2.6 2 mi. SSW of San Fernando 8/8 5:27 pm 34 19.5 118 36.0 2.1 5 mi. SW of Newhall 8/9 5:04 am 36 3.9 117 29.2 2.1 18 mi. S of Panamint Springs 8/9 5:15 am 34 36.7 116 39.1 2.9 20 mi. NE of Lucerne Valley 8/9 7:17 am 34 17.0 118 24.7 2.7 1 mi. E of San Fernando 8/9 11:08 am 34 21.0 118 42.3 2.5 4 mi. N of Simi Valley 8/9 4:55 pm 34 57.9 116 57.2 2.0 6 mi. NE of Barstow 8/9 6:01 pm 35 44.6 118 23.4 2.0 8 mi. NNE of the town of Lake Isabella 8/9 8:50 pm 34 15.3 118 28.5 2.5 2 mi. SW of San Fernando 8/10 10:31 am 35 37.9 118 20.2 2.0 7 mi. E of the town of Lake Isabella 8/10 7:01 pm 32 39.8 115 42.4 2.2 12 mi. SW of El Centro 8/10 7:01 pm 32 40.3 115 41.9 2.0 " 8/10 7:08 pm 32 39.9 115 42.0 2.1 " 8/10 7:22 pm 32 20.4 115 16.8 4.5 25 mi. SSE of Calexico 8/10 7:32 pm 32 40.3 115 42.0 2.3 12 mi. SW of El Centro ------------------------------------------------------------- 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.