SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey October 5, 1995 Weekly Earthquake Report for Southern California ------------------------------------------------ September 28 - October 4, 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, September 28, Pacific Daylight Time, to midnight Wednesday night, October 4, 1995, Pacific Daylight Time. We recorded 1,111 earthquakes during the 7-day period covered. The bulk of the activity this week again consists of aftershocks to the September 20th ML5.8 Ridgecrest quake. 847 of this week's 1,111 belong to that sequence, as did three of the four largerst events. These were a M3.5 and a M3.6 early last Thurday morning, and a M3.8 on Sunday afternoon. The only one of these that produced inquiries was the M3.8. Activity in the rest of the region seems normal. It is time again to summarize the quarterly earthquake statistics. This year, so far, can be compared to the last few preceding years in the following table: 1st quarter 2nd quarter 3rd quarter 4th quarter all 3.0+ all 3.0+ all 3.0+ all 3.0+ 1990 3,483 56 2,627 45 2,225 27 2,403 31 1991 2,041 11 2,218 32 2,445 23 2,651 29 1992 3,618 40 10,288 744 26,238 809 10,700+ 166 1993 4,939 43 5,370 61 5,298 48 4,583 35 1994 10,915 417 5,967 43 5,400 48 5,031 40 1995 3,815 28 3,982 39 8,373 95 The increase this quarter was due to the Ridgecrest sequence; Northridge and Landers/Big Bear aftershocks continued to decline in number as expected. A summary of the major sequences follow: Northridge ---------- 1/17/94 - 9/30/95 Latitude 34.1 - 34.5 North, Longitude 118.3 - 118.85 West All events 12,233 (366 of them this quarter) 3.0 - 3.9 380 4.0 - 4.9 48 5.0 and up 10 Landers/Big Bear ---------------- 4/23/92 - 9/30/95 Latitude 33.8 - 35.33 North, Longitude 116.0 - 117.05 West All events 57,500+ (1,644 of them this quarter) 3.0 - 3.9 1,552 4.0 - 4.9 164 5.0 and up 21 Ridgecrest ---------- 8/17/95 - 9/30/95 Latitude 35.65 - 35.85 North, Longitude 117.55 - 117.75 West All events 4,451 (all of them this quarter) 3.0 - 3.9 57 4.0 - 4.9 6 5.0 and up 2 The table lists the quakes this week that were M2.0 or larger in the central part of the coverage area, except for the Ridgecrest aftershocks since the ML5.8, which must be M2.5 or larger to be listed. 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 ------------------------------------------------------------- 9/28 2:35 am 35 44.0 117 37.6 3.5 8 mi. NNE of Ridgecrest 9/28 4:36 am 35 48.6 117 38.4 3.6 13 mi. N of Ridgecrest 9/28 4:42 pm 35 44.6 117 38.4 2.9 8 mi. N of Ridgecrest 9/28 5:15 pm 35 48.1 117 38.5 2.6 12 mi. N of Ridgecrest 9/28 8:20 pm 35 44.6 117 38.5 3.0 8 mi. N of Ridgecrest 9/28 8:40 pm 36 20.0 120 15.2 2.7 14 mi. NNE of Coalinga 9/29 2:21 am 35 44.4 117 39.0 2.9 8 mi. N of Ridgecrest 9/29 3:06 am 33 26.1 117 3.7 2.4 11 mi. ENE of Fallbrook 9/29 10:21 am 35 49.8 117 25.9 2.4 5 mi. NW of Trona 9/29 4:58 pm 36 4.2 117 43.0 2.1 13 mi. E of Coso Junction 9/29 6:44 pm 34 11.2 118 33.6 2.1 1 mi. SW of Reseda 9/29 11:43 pm 34 15.6 116 26.4 2.0 9 mi. N of Yucca Valley 9/29 11:44 pm 34 15.5 116 26.5 2.1 " 9/30 12:04 am 34 15.4 116 26.3 2.7 " FELT 9/30 5:35 am 36 4.1 117 42.9 2.1 13 mi. E of Coso Junction 9/30 5:46 am 34 56.2 116 45.8 3.5 15 mi. ENE of Barstow FELT 9/30 10:34 am 34 20.0 118 35.8 2.1 4 mi. SSW of Valencia 9/30 12:06 pm 35 48.4 117 38.2 2.5 12 mi. N of Ridgecrest 9/30 1:08 pm 35 47.3 117 40.3 2.5 11 mi. N of Ridgecrest 9/30 4:19 pm 33 59.5 116 41.3 2.0 7 mi. WSW of Morongo Valley 9/30 7:32 pm 34 29.2 120 42.8 2.2 7 mi. SSW of Pt. Arguello 10/1 2:30 am 32 20.7 115 7.0 2.6 31 mi. SE of Calexico 10/1 3:06 am 32 20.4 115 7.7 2.6 " 10/1 4:12 am 35 47.6 117 40.0 2.0 11 mi. N of Ridgecrest 10/1 7:18 am 35 44.3 117 37.4 2.8 8 mi. NNE of Ridgecrest 10/1 7:50 am 35 44.3 117 37.8 2.5 " 10/1 9:30 am 35 44.0 117 37.7 3.3 7 mi. NNE of Ridgecrest 10/1 2:27 pm 35 1.5 118 59.5 3.0 3 mi. WNW of Wheeler Ridge 10/1 3:02 pm 35 44.0 117 37.7 2.6 7 mi. NNE of Ridgecrest 10/1 4:42 pm 35 44.3 117 37.6 3.3 8 mi. NNE of Ridgecrest 10/1 5:10 pm 35 48.6 117 38.7 3.8 13 mi. N of Ridgecrest FELT 10/2 1:16 am 33 47.0 116 8.7 2.0 6 mi. NE of Indio 10/2 5:41 am 34 55.4 116 54.4 2.1 7 mi. ENE of Barstow 10/2 1:28 pm 35 44.1 117 37.5 2.6 8 mi. NNE of Ridgecrest 10/2 3:50 pm 35 45.8 117 38.1 2.5 9 mi. N of Ridgecrest 10/2 6:00 pm 35 30.0 119 14.6 2.0 16 mi. WNW of Bakersfield 10/2 6:33 pm 35 47.0 117 37.5 3.4 11 mi. NNE of Ridgecrest 10/2 10:00 pm 35 43.7 117 37.8 2.5 7 mi. NNE of Ridgecrest 10/3 3:08 am 35 44.7 117 38.4 2.7 8 mi. N of Ridgecrest 10/3 4:07 am 35 0.1 116 57.5 2.1 8 mi. NNE of Barstow 10/3 6:03 am 34 57.6 119 23.5 2.0 12 mi. SSE of Taft 10/3 6:52 am 32 27.0 115 15.6 2.3 20 mi. SE of Calexico 10/3 8:42 am 34 38.7 116 29.1 2.3 29 mi. ENE of Lucerne Valley 10/3 9:46 am 34 14.2 118 28.1 2.0 1 mi. NW of Panorama City 10/3 1:21 pm 34 21.4 116 26.9 2.0 16 mi. N of Yucca Valley 10/3 3:00 pm 32 59.8 116 23.1 2.9 13 mi. ESE of Julian 10/3 6:54 pm 33 33.3 117 10.9 2.4 12 mi. NNE of Fallbrook 10/3 7:01 pm 33 33.4 117 10.8 2.0 11 mi. SE of Lake Elsinore 10/3 9:33 pm 33 28.8 116 26.4 2.0 15 mi. NNW of Borrego Springs 10/3 9:56 pm 34 9.5 116 26.2 2.0 2 mi. N of Yucca Valley 10/4 4:38 am 35 48.4 117 38.5 2.8 12 mi. N of Ridgecrest 10/4 5:52 am 35 31.9 118 25.0 2.1 7 mi. SSE of town of Lake Isabella 10/4 3:45 pm 35 46.9 117 39.3 2.9 11 mi. N of Ridgecrest 10/4 6:06 pm 35 44.4 117 37.5 2.8 8 mi. NNE of Ridgecrest -------------------------------------------------------------