SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey August 7, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ July 31 - August 6, 1997 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 818-395-6327. For daily updates, call our Earthquake Information Hotline: 818-395-6977. -------------------------------- This week's Report covers the time period from midnight Thursday morning, July 31, Universal Time (ie. GMT), to midnight Wednesday night, August 6, Universal Time. In local time, the period of coverage is from 5 p.m., July 30, Pacific Daylight Time, to 5 p.m., August 6, Pacific Daylight Time. We detected 290 earthquakes during the seven-day period covered. These Weekly Reports should not be used for archival purposes. Further data processing often changes the magnitudes slightly and, especially during times of high seismicity, sometimes changes the estimates of total seismicity. For the best earthquake catalog currently available, see: http://scec.gps.caltech.edu/catalog-search.html This week's seismicity was a good deal quieter than last week's. Our largest quake was a M3.1 Northridge aftershock, extremely early on Monday morning. It was felt by several people in the Reseda area. Like the great majority of the Northridge aftershocks, it had a thrust focal mechanism. There was one more quake reported felt. That was a M2.7 in the Loma Linda/Redlands area, on Friday night. It was not an aftershock; however, the epicenter, near the intersection of the Banning Fault and the San Jacinto Fault, is a very common one. The focal mechanism was normal (tensional), which is normal for that area, where the San Andreas and San Jacinto Faults form a graben that we call the San Bernardino Valley. There was also a fair amount of activity south of the U.S./Mexico border, including three M3+ events, in the wee hours of last Thursday morning. As far as we know, however, none of these were felt in the U.S. Table 1 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 ------------------------------------------------------------- 7/30 6:19 pm 35 35.7 118 21.7 2.4 6 mi. ESE of town of Lake Isabella 7/30 10:12 pm 34 20.4 116 28.0 2.5 15 mi. N of Yucca Valley 7/31 1:01 am 32 23.6 115 10.9 3.1 26 mi. SE of Calexico 7/31 1:13 am 32 24.6 115 10.5 2.9 " 7/31 1:15 am 32 23.2 115 9.9 2.5 " 7/31 1:34 am 32 23.9 115 10.4 2.6 " 7/31 1:39 am 32 32.5 115 4.1 2.3 26 mi. ESE of Calexico 7/31 1:41 am 32 23.3 115 10.3 2.3 27 mi. SE of Calexico 7/31 4:04 am 32 23.7 115 10.3 2.9 " 7/31 4:41 am 32 23.3 115 10.6 3.0 " 7/31 4:43 am 32 24.0 115 11.0 3.1 " 7/31 6:37 am 34 20.4 116 28.0 2.4 15 mi. N of Yucca Valley 7/31 3:00 pm 35 58.8 117 40.8 2.2 15 mi. ESE of Coso Junction 7/31 7:07 pm 32 23.3 115 10.2 2.5 27 mi. SE of Calexico 7/31 7:37 pm 35 58.8 117 40.9 2.4 15 mi. ESE of Coso Junction 7/31 7:48 pm 35 58.8 117 40.9 2.4 " 7/31 10:01 pm 34 43.5 120 7.6 2.1 8 mi. NNE of Buellton 7/31 10:25 pm 35 58.7 117 40.7 2.1 15 mi. ESE of Coso Junction 8/1 1:59 am 34 20.0 116 27.7 2.0 14 mi. N of Yucca Valley 8/1 8:19 am 32 59.5 117 42.9 2.0 23 mi. SW of Oceanside 8/1 12:04 pm 32 27.9 115 27.0 2.7 14 mi. S of Calexico 8/1 12:41 pm 34 23.4 116 27.7 2.0 18 mi. N of Yucca Valley 8/1 5:36 pm 32 45.2 115 26.1 2.0 6 mi. NNE of Calexico 8/1 6:13 pm 32 29.0 115 26.6 2.2 13 mi. SSE of Calexico 8/1 8:39 pm 33 18.1 116 13.8 2.0 8 mi. ENE of Borrego Springs 8/1 9:35 pm 34 1.6 117 14.0 2.7 1 mi. SE of Loma Linda FELT 8/1 9:44 pm 32 28.7 115 26.5 2.6 13 mi. SSE of Calexico 8/2 1:38 pm 35 47.8 117 38.3 2.7 12 mi. N of Ridgecrest 8/2 6:13 pm 35 35.3 116 52.8 2.3 16 mi. N of Goldstone Lake 8/2 11:28 pm 35 32.0 118 22.9 2.2 8 mi. SE of town of Lake Isabella 8/3 7:44 am 34 37.6 116 31.0 2.0 27 mi. ENE of Lucerne Valley 8/3 9:24 am 36 5.5 117 52.8 2.0 5 mi. NE of Coso Junction 8/3 3:29 pm 34 10.9 116 26.0 2.3 4 mi. N of Yucca Valley 8/3 10:00 pm 32 42.2 115 54.2 2.1 5 mi. ESE of Ocotillo 8/4 12:03 am 34 12.1 118 33.9 3.1 1 mi. W of Reseda FELT 8/5 11:16 am 35 31.3 116 51.7 2.7 11 mi. N of Goldstone Lake 8/6 12:53 am 33 35.2 118 14.8 2.1 8 mi. SSE of Pt. Fermin, San Pedro -------------------------------------------------------------