SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey July 13, 1995 Weekly Earthquake Report for Southern California ------------------------------------------------ July 6 - 12, 1995 Prepared by: Kate Hutton, Seismological Laboratory (kate@bombay.gps.caltech.edu) Lucy Jones, U.S. Geological Survey California Institute of Technology 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 6, Pacific Daylight Time, to midnight Wednesday night, July 12, 1995, Pacific Daylight Time. We recorded 276 earthquakes of during the 7-day period covered. For simplicity's sake, we have started including all the recorded quakes rather than only those above M1.0. Since most of the quakes we record are larger than this, the difference will be slight, and should only affect the weekly totals and the map. Of the 276, 241 had magnitudes of M1.0 or larger. The largest quake this week was a M3.3 that occurred Friday afternoon in the Coast Ranges north-northwest of Taft. There were also two more M3's: one between Corona and Chino (M3.2) late Sunday evening and one at Wheeler Ridge, near the Grapevine Grade (M3.1) on Tuesday afternoon. Both the Taft and Wheeler Ridge earthquakes were part occurred in the compressional belt that lies between the San Andreas Fault and the Central Valley. The Taft earthquake was deep for Southern California (below 15 km depth), within the system of buried faults that produced the 1983 Coalinga and 1985 Avenal earthquakes, but south of those two events. The Wheeler Ridge earthquake resulted from thrust faulting within the old aftershock zone of the 1952 Kern County (Mw7.5) earthquake. The Chino quake was a strike-slip event within a band of earthquakes that we call the Fontana trend. That trend strikes northeast from the northern end of the Elsinore Fault, near the Puente Hills, to the northern part of the San Jacinto Fault near San Bernardino. It is a common source of small (M2-M3) earthquakes and is probably a left-lateral strike-slip fault whose surface expression is obscured by the recent sediments of the San Bernardino Valley. All in all, it was not a very exciting week. The table lists the quakes this week 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 Pacific Daylight Time or 8 hrs to the Pacific Standard Time listed. Table 1 ------- Date Time N Lat. W Long. Mag ------------------------------------------------------------- 7/6 3:29 pm 34 21.9 118 31.8 2.0 Under Newhall 7/6 5:30 pm 32 33.8 117 20.1 2.5 15 mi. W of Chula Vista 7/7 12:59 pm 34 21.3 118 33.6 2.2 2 mi. SW of Newhall 7/7 4:06 pm 34 16.6 118 26.5 2.2 Under San Fernando 7/7 5:26 pm 35 24.2 119 32.0 3.3 18 mi. NNW of Taft 7/7 7:01 pm 34 15.8 118 28.5 2.0 2 mi. WSW of San Fernando 7/8 8:34 am 32 35.9 117 19.5 2.0 12 mi. W of Chula Vista 7/8 11:51 am 35 2.0 116 59.9 2.3 10 mi. N of Barstow 7/8 1:35 pm 36 4.8 120 10.0 2.8 11 mi. ESE of Coalinga 7/9 12:54 am 33 46.6 116 8.4 2.6 6 mi. NE of Indio 7/9 5:12 am 34 25.1 118 38.9 2.8 3 mi. W of Magic Mtn. FELT 7/9 4:27 pm 34 55.3 116 46.5 2.3 14 mi. E of Barstow 7/9 10:35 pm 33 58.1 117 35.9 3.2 6 mi. NNW of Corona FELT 7/9 10:41 pm 33 58.2 117 35.8 2.1 " 7/10 6:56 am 34 19.7 118 36.2 2.3 5 mi. SW of Newhall 7/10 8:06 am 32 58.7 117 41.3 2.0 23 mi. SW of Oceanside 7/10 1:40 pm 35 20.9 117 54.5 2.3 23 mi. SW of Ridgecrest 7/10 2:37 pm 36 0.7 117 48.7 2.1 Coso Range, 7 mi. ESE of Coso Junction 7/10 4:56 pm 33 58.3 116 57.9 2.6 3 mi. NNE of Beaumont 7/10 5:34 pm 34 14.1 116 50.0 2.0 2 mi. SSE of Big Bear City 7/11 12:27 am 34 20.8 118 27.1 2.5 4 mi. N of San Fernando 7/11 5:02 am 34 17.5 118 29.6 2.6 3 mi. WNW of San Fernando 7/11 4:43 pm 35 1.9 118 59.8 3.1 Wheeler Ridge, 2 mi. WNW of the I5/99 interchange 7/11 8:12 pm 32 44.0 115 56.3 2.1 3 mi. E of Ocotillo 7/12 12:31 am 36 15.0 120 21.5 2.5 7 mi. N of Coalinga 7/12 4:18 am 36 0.3 117 48.6 2.1 8 mi. ESE of Coso Junction 7/12 10:26 am 32 30.4 115 30.9 2.2 11 mi. S of Calexico 7/12 10:29 am 34 55.2 116 46.5 2.2 14 mi. E of Barstow 7/12 7:52 pm 36 2.9 120 30.0 2.5 11 mi. NNW of Parkfield 7/12 8:04 pm 33 4.6 117 50.9 2.3 27 mi. SSW of San Clemente 7/12 11:19 pm 34 55.5 116 46.3 2.0 14 mi. E of Barstow -------------------------------------------------------------