SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey August 14, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ August 7 - 13, 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, August 7, Universal Time (ie. GMT), to midnight Wednesday night, August 13, Universal Time. In local time, the period of coverage is from 5 p.m., August 6, Pacific Daylight Time, to 5 p.m., August 13, Pacific Daylight Time. We detected 397 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 The activity south of the U.S./Mexico border continued this week. The largest event was a M3.6 on Sunday afternoon, which was felt in the Yuma, Arizona area. Of the earthquakes within our seismographic network, the largest was a member of the on-going cluster between the San Andreas and San Jacinto Faults in the San Bernardino area. It occurred on Wednesday morning and had a magnitude of M3.1. Previous events in this cluster include: a M4.2 on June 28, 1997, a M3.5 on July 12, and a M3.7 on July 26. These events show "normal" focal mechanisms, showing tension in the crust associated with the graben (down-dropped block) between the two major faults. One more quake this week was felt: a M3.7 near San Clemente Island on Tuesday morning. 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 ------------------------------------------------------------- 8/6 8:44 pm 34 33.0 116 31.3 2.0 25 mi. ENE of Lucerne Valley 8/6 8:46 pm 34 33.4 116 31.0 2.0 " 8/6 8:54 pm 34 58.3 116 49.0 2.0 12 mi. ENE of Barstow 8/7 7:28 am 35 16.2 118 54.1 2.2 6 mi. NW of Arvin 8/7 8:08 am 34 38.4 116 29.9 2.1 28 mi. ENE of Lucerne Valley 8/7 2:01 pm 33 3.1 116 11.1 2.5 7 mi. SSW of Ocotillo Wells 8/7 5:00 pm 34 1.5 117 14.2 2.4 1 mi. SSE of Loma Linda 8/7 5:01 pm 34 1.1 117 14.4 2.3 " 8/7 5:05 pm 34 37.3 116 38.6 2.3 21 mi. NE of Lucerne Valley 8/7 5:15 pm 32 19.3 115 15.4 2.5 27 mi. SSE of Calexico 8/7 7:57 pm 34 28.1 116 30.8 2.2 24 mi. N of Yucca Valley 8/7 10:16 pm 34 15.9 118 28.7 2.3 1 mi. ESE of Granada Hills 8/8 2:59 pm 32 37.8 117 53.6 2.4 29 mi. ESE of San Clemente Is. (SE tip) 8/8 9:41 pm 32 42.3 115 54.0 2.2 5 mi. ESE of Ocotillo 8/8 10:14 pm 33 19.4 116 21.2 2.5 4 mi. NNE of Borrego Springs 8/9 7:18 am 35 33.1 120 1.3 2.4 13 mi. N of Simmler 8/9 10:19 am 34 9.1 116 26.0 2.5 2 mi. NNE of Yucca Valley 8/9 10:28 am 34 9.0 116 26.1 2.8 " 8/9 4:40 pm 32 17.8 115 7.2 3.1 33 mi. SE of Calexico 8/9 4:51 pm 32 19.9 115 6.2 2.6 " 8/9 5:54 pm 32 18.8 115 7.1 3.0 " 8/9 6:00 pm 32 18.1 115 7.2 2.9 " 8/9 6:48 pm 32 18.6 115 7.6 2.7 " 8/9 6:50 pm 32 18.4 115 7.2 3.1 " 8/9 7:14 pm 32 19.3 115 6.9 2.5 " 8/9 9:59 pm 32 19.0 115 6.7 2.5 " 8/9 11:02 pm 32 18.3 115 7.7 3.0 " 8/9 11:06 pm 33 60.0 117 10.5 2.5 3 mi. S of Redlands 8/9 11:28 pm 34 35.5 116 37.2 2.2 21 mi. ENE of Lucerne Valley 8/10 3:16 am 34 33.9 116 31.1 2.5 25 mi. ENE of Lucerne Valley 8/10 8:39 am 35 17.8 118 35.4 2.3 14 mi. NW of Tehachapi 8/10 2:48 pm 32 17.6 115 7.6 2.8 33 mi. SE of Calexico 8/10 3:09 pm 32 18.1 115 7.6 3.6 " FELT 8/10 3:27 pm 32 17.5 115 5.8 2.7 " 8/10 3:50 pm 32 19.1 115 5.7 2.8 " 8/10 4:20 pm 36 1.3 117 50.5 2.3 6 mi. ESE of Coso Junction 8/10 4:43 pm 32 19.9 115 7.0 2.5 33 mi. SE of Calexico 8/10 4:43 pm 32 17.0 115 7.3 2.6 " 8/10 4:45 pm 32 20.5 115 6.1 2.7 " 8/10 6:17 pm 33 51.9 117 50.2 2.1 2 mi. SW of Yorba Linda 8/10 6:54 pm 32 20.1 115 5.7 2.5 33 mi. SE of Calexico 8/11 3:17 am 32 18.0 115 7.8 2.7 " 8/11 4:30 am 32 18.6 115 7.4 2.7 " 8/11 11:44 am 32 20.0 115 7.3 2.8 " 8/11 1:34 pm 34 13.5 118 54.6 2.1 4 mi. SSW of Moorpark 8/11 5:43 pm 35 1.7 116 58.4 2.1 10 mi. NNE of Barstow 8/11 8:31 pm 34 13.8 118 54.1 2.2 3 mi. SSW of Moorpark 8/12 4:43 am 32 18.9 115 6.2 2.5 33 mi. SE of Calexico 8/12 5:34 am 32 50.1 118 23.8 3.7 3 mi. WNW of San Clemente Is. (SE tip) FELT 8/12 6:09 am 32 17.9 115 7.4 2.6 33 mi. SE of Calexico 8/12 8:13 pm 32 13.4 115 35.5 2.8 " 8/12 9:14 pm 35 56.0 117 37.4 2.1 18 mi. NW of Trona 8/13 4:48 am 32 51.1 118 22.2 2.6 2 mi. NNW of San Clemente Is. (SE tip) 8/13 7:43 am 34 9.0 117 20.0 3.1 3 mi. NW of San Bernardino; FELT 8/13 8:02 am 32 17.6 115 7.6 3.0 33 mi. SE of Calexico 8/13 9:02 am 36 3.9 117 38.4 2.0 17 mi. E of Coso Junction -------------------------------------------------------------