SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey October 9, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ October 2 - 8, 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, October 2, Universal Time (ie. UTC), to midnight Wednesday night, October 8, Universal Time. In local time, the period of coverage is from 5 p.m., October 1, Pacific Daylight Time, to 5 p.m., October 8, Pacific Daylight Time. We detected 219 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 Aside from the two M3 events in Parkfield, for which the reader should refer to the Northern California Earthquake Report, there were three M3+ quakes in our region this week. The first occurred on Friday night in the San Gabriel Mtns., between San Fernando and Elizabeth Lake (eight miles away from the San Andreas Fault). It has a magnitude of M3.1 and a strike-slip focal mechanism, with a north-south or east-west fault plane. (Remember that the seismological focal mechanism is always ambiguous, unless you know something else about the quake; there are always two possible fault planes.) Because the epicentral area is unpopulated, there were no 'felt' reports. The second event was in the late morning on Monday, in Death Valley. It had a magnitude of M3.4, making it the largest quake of the week. Our network is sparse in that region; however, the focal mechanism is consistent with strike-slip at an strike similar to mapped faults in the area. The third M3 (M3.1 to be exact) occurred the same day, in the afternoon, and was a Northridge aftershock. It had a thrust mechanism and was widely felt in San Fernando Valley and Hollywood. 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 ------------------------------------------------------------- 10/1 5:23 pm 36 5.9 117 53.6 2.3 4 mi. NE of Coso Junction 10/1 9:52 pm 35 47.2 116 38.6 2.0 24 mi. WSW of Shoshone 10/2 1:34 am 34 20.7 116 27.7 2.3 15 mi. N of Yucca Valley 10/2 2:22 am 35 47.2 117 39.6 2.0 11 mi. N of Ridgecrest 10/2 11:33 am 34 15.5 119 22.4 2.6 4 mi. WSW of Ventura 10/2 4:27 pm 33 4.1 115 34.9 2.0 3 mi. NE of Westmorland 10/2 9:36 pm 32 47.6 115 26.6 2.4 6 mi. E of El Centro 10/2 11:28 pm 36 6.8 117 52.1 2.0 6 mi. NE of Coso Junction 10/3 3:49 am 33 11.8 115 34.0 2.1 3 mi. SW of Niland 10/3 9:41 am 34 21.3 116 27.6 2.2 16 mi. N of Yucca Valley 10/3 3:02 pm 32 42.8 115 54.5 2.0 5 mi. ESE of Ocotillo 10/3 8:52 pm 34 8.6 117 20.1 2.5 3 mi. NE of Rialto 10/3 8:55 pm 36 4.2 119 51.0 2.5 28 mi. E of Coalinga 10/3 10:10 pm 34 30.0 118 19.4 3.1 11 mi. SSE of Elizabeth Lake 10/4 1:41 am 33 42.2 116 50.8 2.2 7 mi. ESE of Hemet 10/4 12:36 pm 34 38.9 116 31.1 2.9 28 mi. ENE of Lucerne Valley 10/4 2:08 pm 34 20.5 116 28.2 2.3 15 mi. N of Yucca Valley 10/5 12:06 am 34 6.8 117 19.8 2.2 2 mi. WNW of San Bernardino 10/5 7:06 am 34 16.9 116 46.0 2.3 5 mi. ENE of Big Bear City 10/5 7:37 am 33 33.9 118 20.7 2.1 10 mi. SSW of Pt. Fermin, San Pedro 10/5 7:55 am 34 10.2 117 19.6 2.1 4 mi. NNW of San Bernardino 10/5 9:08 am 33 41.7 117 59.4 2.4 2 mi. SW of Fountain Valley 10/5 4:10 pm 33 46.9 116 58.9 2.1 2 mi. NNW of Hemet 10/5 4:28 pm 35 57.3 120 31.5 3.0 6 mi. NW of Parkfield 10/6 8:07 am 34 28.1 116 30.9 2.2 24 mi. N of Yucca Valley 10/6 11:29 am 35 46.8 116 38.8 3.4 24 mi. WSW of Shoshone 10/6 2:27 pm 34 15.9 118 28.3 3.1 1 mi. ESE of Granada Hills FELT in S.F. Valley, Hollywood 10/7 7:36 pm 35 58.0 117 58.6 2.2 5 mi. SSW of Coso Junction 10/7 8:25 pm 33 1.1 117 51.0 2.1 31 mi. SSW of Dana Point 10/7 8:34 pm 35 56.2 120 32.2 3.1 6 mi. WNW of Parkfield 10/8 1:24 am 33 41.9 115 57.0 2.1 11 mi. N of North Shore 10/8 9:59 am 33 33.1 118 7.8 2.1 10 mi. SSW of Bolsa Chica Beach 10/8 1:10 pm 33 30.3 116 26.4 2.0 15 mi. S of Palm Desert -------------------------------------------------------------