SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey September 25, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ September 18 - 24, 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 626-395-6327. For daily updates, call our Earthquake Information Hotline: 626-395-6977. -------------------------------- ***************************************************************** If you receive this Report by FAX and if you have recently had a change of AREA CODE, please notify us ASAP. We have no other way to know which fax numbers need to be changed!! Actually, if your area code is 818 and it HASN'T changed, it would be helpful to know that, too. ***************************************************************** This week's Report covers the time period from midnight Thursday morning, September 18, Universal Time (ie. UTC), to midnight Wednesday night, September 24, Universal Time. In local time, the period of coverage is from 5 p.m., September 17, Pacific Daylight Time, to 5 p.m., September 24, Pacific Daylight Time. We detected 224 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 biggest excitement for this week was a M4.1 in the San Bernardino Mtns., south of Big Bear, on Friday afternoon. It was widely felt in the Big Bear and San Bernardino areas. There was a small foreshock (M2.2) an hour and a half beforehand, and a few small aftershocks. These quakes are within the after- shock zone of the 1992 Big Bear quake (Mw6.4), which was itself an aftershock of the Landers (Mw7.3) quake. The M4.1 had a strike-slip mechanism, which has been typical of events in that area. 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 ------------------------------------------------------------- 9/17 6:45 pm 34 59.0 116 56.7 2.5 7 mi. NE of Barstow 9/18 5:36 am 33 56.3 116 1.3 2.1 13 mi. S of Twentynine Palms 9/18 7:00 am 33 47.8 118 18.1 2.5 2 mi. SSW of Carson 9/18 7:41 am 33 56.2 116 1.4 2.0 13 mi. S of Twentynine Palms 9/19 5:06 am 34 36.0 116 16.4 2.5 32 mi. N of Joshua Tree 9/19 7:31 am 34 24.9 118 59.0 2.6 3 mi. WNW of Fillmore 9/19 1:40 pm 34 2.2 116 21.8 2.2 7 mi. SSW of Joshua Tree 9/19 2:07 pm 34 8.6 116 51.3 2.2 3 mi. NNW of Mt. San Gorgonio 9/19 3:37 pm 34 8.4 116 51.4 4.1 " FELT 9/19 3:39 pm 34 8.7 116 51.3 2.0 " 9/19 3:40 pm 33 1.4 117 49.3 2.6 30 mi. SSW of San Clemente 9/20 6:48 pm 34 15.1 117 49.5 2.6 8 mi. NNE of Glendora 9/20 9:05 pm 35 35.4 118 21.4 2.9 6 mi. ESE of town of Lake Isabella 9/20 11:45 pm 36 7.4 117 40.8 2.2 15 mi. ENE of Coso Junction 9/21 2:45 am 34 19.9 116 27.9 2.4 14 mi. N of Yucca Valley 9/21 2:55 am 32 32.5 115 38.7 2.3 12 mi. SW of Calexico 9/21 7:00 am 36 10.3 118 3.8 2.1 8 mi. SSW of Olancha 9/21 8:04 am 34 8.5 116 52.7 2.0 4 mi. NW of Mt. San Gorgonio 9/21 1:19 pm 34 18.5 118 33.5 2.3 4 mi. NW of Granada Hills 9/21 2:20 pm 35 47.2 117 39.7 2.2 11 mi. N of Ridgecrest 9/21 4:17 pm 35 47.4 117 39.2 2.0 " 9/21 5:10 pm 34 9.7 116 51.7 2.0 4 mi. NNW of Mt. San Gorgonio 9/21 6:03 pm 33 30.5 116 27.9 2.0 12 mi. ESE of Anza 9/21 8:22 pm 34 2.2 116 22.2 2.0 7 mi. SE of Yucca Valley 9/22 6:13 am 34 58.7 116 57.4 2.3 7 mi. NNE of Barstow 9/22 7:51 pm 34 9.1 117 20.0 2.2 3 mi. NE of Rialto 9/23 6:39 am 33 0.4 117 46.8 2.0 26 mi. WSW of Oceanside 9/23 6:54 am 34 8.5 116 51.1 2.1 3 mi. NNW of Mt. San Gorgonio 9/23 1:34 pm 33 33.1 118 19.0 2.1 10 mi. S of Pt. Fermin, San Pedro 9/24 4:52 am 34 7.8 117 28.4 2.0 2 mi. NW of Fontana 9/24 9:25 am 32 57.6 117 43.5 2.1 25 mi. SW of Oceanside 9/24 9:42 am 34 27.3 117 56.0 2.0 13 mi. SE of Palmdale -------------------------------------------------------------