SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey July 10, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ July 2 - 9, 1997 Prepared by: Nick Scheckel, 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 Wednesday morning, July 2, Universal Time (ie. GMT), to midnight Wednesday night, July 9, Universal Time. In local time, the period of coverage is from 5 p.m., July 1, Pacific Daylight Time, to 5 p.m., July 9, Pacific Daylight Time. We detected 399 earthquakes during the eight-day period covered. The Weekly Report this week is longer in order to make up for a day lost due to last week's holiday. 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 largest earthquake this week, a M4.3, occurred near Ridgecrest on Thursday morning and was felt in the area. A pair of M3.5's occurred near the border town of Calexico, the first around noon on Thursday and the second, which was much closer, on Saturday morning. Caltech received no official word that either or both were felt though it's likely only the second one was due to it's proximity. Back up north, on the morning of Wednesday the 2nd, a M3.3 aftershock to the M5.3 Coso earthquake (November 27, 1996) shook the Little Lake area. No felt reports were received. We have a brief summary this week of the quarterly statistics: Totals listed below apply to the area within a polygon bounded by the following latitude, longitude pairs: 35.0N, 121.0W; 37.0N, 119.0W; 37.0N, 115.0W; 32.5N, 115.0W; and 32.5N, 121.0W. 1st quarter 2nd quarter 3rd quarter 4th quarter all 3.0+ all 3.0+ all 3.0+ all 3.0+ 1986 3,040 16 2,865 19 6,634 192 2,300 38 1987 1,679 24 1,887 36 2,341 38 5,748 198 1988 2,749 40 2,128 45 2,195 30 2,208 27 1989 2,528 46 2,340 21 2,323 19 2,335 26 1990 2,850 56 2,293 43 1,859 27 2,039 31 1991 1,679 10 1,843 32 2,081 21 2,337 27 1992 3,389 37 10,084 741 25,849 808 9,775 181 1993 4,799 41 5,152 58 5,039 46 4,419 34 1994 10,735 418 5,766 42 5,221 48 4,813 39 1995 3,639 28 3,788 37 8,252 88 7,733 49 1996 5,735 56 3,966 32 3,690 23 4,660 50 1997 3,699 39 3,276 54 Northridge ---------- 1/17/94 - 3/31/97 Latitude 34.1 - 34.5 North, Longitude 118.3 - 118.85 West All events 14,204 (519 of them this quarter) 3.0 - 3.9 405 (12 of them this quarter) 4.0 - 4.9 52 (1 of them this quarter) 4.8 on April 27 5.0 and up 11 (1 of them this quarter) 5.1 on April 26 Landers/Big Bear ---------------- 4/23/92 - 3/31/97 Latitude 33.8 - 35.33 North, Longitude 116.0 - 117.05 West All events 66,846 (715 of them this quarter) 3.0 - 3.9 1,631 (14 of them this quarter) 4.0 - 4.9 169 (none this quarter) 5.0 and up 23 (none this quarter) 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 ------------------------------------------------------------- 7/1 7:07 pm 35 47.6 117 38.0 2.2 12 mi. N of Ridgecrest 7/2 6:52 am 36 5.8 117 40.0 3.3 16 mi. ENE of Coso Junction 7/2 1:52 pm 33 18.4 118 19.0 2.1 2 mi. S of Avalon, Catalina Island 7/2 6:57 pm 35 35.8 118 21.8 2.6 6 mi. ESE of town of Lake Isabella 7/2 11:18 pm 34 58.4 116 48.6 2.8 13 mi. ENE of Barstow 7/3 2:13 am 32 30.3 118 12.3 2.4 23 mi. SSE of San Clemente Is. (SE tip) 7/3 10:49 am 35 47.5 117 38.3 4.3 11 mi. N of Ridgecrest FELT 7/3 10:50 am 35 47.8 117 38.5 2.5 12 mi. N of Ridgecrest 7/3 12:17 pm 32 11.6 115 24.7 3.5 33 mi. S of Calexico 7/3 1:53 pm 32 55.0 117 41.4 2.5 26 mi. SW of Oceanside 7/3 6:13 pm 35 47.9 117 38.2 2.0 12 mi. N of Ridgecrest 7/3 6:13 pm 33 42.5 116 45.8 2.0 3 mi. SW of Idyllwild 7/3 6:37 pm 33 56.1 118 42.7 2.3 7 mi. SSW of Malibu 7/4 2:09 am 35 55.2 116 10.0 2.0 7 mi. ESE of Shoshone 7/4 2:33 am 35 47.1 117 38.0 2.0 11 mi. N of Ridgecrest 7/5 12:05 am 34 12.9 117 28.0 2.0 3 mi. W of Devore 7/5 1:25 am 35 55.9 117 37.1 2.0 17 mi. NW of Trona 7/5 2:25 am 35 47.5 117 38.0 2.1 11 mi. N of Ridgecrest 7/5 5:41 am 32 42.9 115 24.9 2.5 5 mi. NE of Calexico 7/5 5:42 am 32 42.7 115 25.0 3.5 5 mi. ENE of Calexico 7/5 7:38 am 33 10.6 115 35.5 2.3 2 mi. E of Obsidian Butte 7/5 9:49 am 35 47.4 117 38.1 2.6 11 mi. N of Ridgecrest 7/5 9:37 pm 35 47.4 117 37.6 2.0 " 7/5 9:38 pm 35 47.2 117 37.9 2.4 " 7/7 2:27 am 35 2.2 116 59.0 2.1 10 mi. NNE of Barstow 7/7 5:59 am 34 33.0 116 32.5 2.3 24 mi. ENE of Lucerne Valley 7/7 9:45 am 34 8.4 116 26.0 2.1 1 mi. NNE of Yucca Valley 7/7 5:28 pm 34 9.9 117 20.0 2.1 4 mi. NNE of Rialto 7/8 2:01 am 33 11.0 115 35.3 2.0 2 mi. ENE of Obsidian Butte 7/8 3:05 am 32 36.6 115 54.7 2.0 9 mi. SSE of Ocotillo 7/8 4:17 pm 34 27.6 116 30.8 2.4 23 mi. N of Yucca Valley 7/8 8:37 pm 35 59.7 117 40.5 2.0 15 mi. ESE of Coso Junction 7/8 10:30 pm 34 26.1 118 36.9 2.7 4 mi. NW of Valencia 7/9 4:46 am 33 15.6 115 59.4 2.0 1 mi. SW of Salton City 7/9 4:19 pm 34 15.2 117 4.7 2.0 3 mi. NNE of Running Springs 7/9 4:44 pm 34 9.1 117 20.0 2.3 3 mi. NNE of Rialto -------------------------------------------------------------