SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey May 29, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ May 21 - 28, 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, May 21, Universal Time (ie. GMT), to midnight Wednesday night, May 28, Universal Time. In local time, the period of coverage is from 5 p.m., May 20, Pacific Daylight Time, to 5 p.m., May 28, Pacific Daylight Time. We detected 355 earthquakes during the eight-day period covered. This week's Report covers an eight-day period because last week's Report mistakenly covered only six days. We apologize for the mistake, although, judging from small number of complaints (ie. none), not many readers noticed. This Report 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 available, see http://scec.gps.caltech.edu/catalog-search.html. Southern California experienced moderately high seismic activity this week, including one M4.0 and six M3+ events in our reporting area (two other M3+ events were recorded by our network in northern Baja California and a M3.0 near Parkfield. See the report from the U.S.G.S. Menlo Park for information on the latter event). In spite of all this activity, we received no public inquiries. The M4.0 was a Ridgecrest earthquake on Friday evening. It occurred in the same area as the Ridgecrest swarms of 1995 and 1996, which included two M5+ events. It is a problematic as to whether we should call this an aftershock, because the rate of earthquakes in this region is only a factor of two or three higher than it was before the mainshock. This week's focal mechanism was similar to the 1995 aftershocks, with right-lateral strike-slip motion on a plane striking 20 degrees west of north. Four of the M3+ events were Landers aftershocks (of the Mw7.3 on June 28, 1992), in the Barstow area. These were: a M3.6 on Thursday night, a M3.5 and a M3.3 on Friday morning, and a M3.0 near noon on Friday. All, like most Landers aftershocks, were strike-slip. Another M3.0 Landers aftershock, at a different location near the center of the Landers rupture, occurred last Wednesday afternoon. We also had a M3.5 near Julian on Friday morning. This quake was very near the Elsinore Fault and had a strike-slip mechanism consistent with that fault. 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 ------------------------------------------------------------- 5/20 5:37 pm 35 43.7 119 15.9 2.1 27 mi. SSW of Porterville 5/20 9:53 pm 35 59.7 120 32.2 2.6 8 mi. NW of Parkfield 5/21 7:07 am 32 11.5 115 46.3 3.3 36 mi. SSW of Calexico 5/21 7:30 am 33 11.8 115 34.6 2.0 3 mi. ENE of Obsidian Butte 5/21 2:49 pm 33 30.6 116 19.8 2.2 14 mi. SSE of Palm Desert 5/21 4:32 pm 34 37.8 116 32.3 3.0 26 mi. ENE of Lucerne Valley 5/21 4:45 pm 34 37.7 116 32.4 2.2 " 5/21 4:46 pm 34 37.9 116 32.5 2.1 " 5/21 4:55 pm 34 37.7 116 32.3 2.2 " 5/21 5:01 pm 34 37.6 116 32.3 2.2 " 5/21 6:11 pm 33 55.5 116 58.6 2.1 Under Beaumont 5/21 8:23 pm 36 16.0 120 20.5 2.6 8 mi. N of Coalinga 5/22 12:25 pm 32 16.1 116 40.0 3.2 29 mi. SE of San Ysidro 5/22 8:01 pm 32 33.5 115 48.6 2.7 16 mi. SE of Ocotillo 5/22 11:48 pm 34 58.3 116 48.6 3.6 13 mi. ENE of Barstow 5/23 4:12 am 34 14.9 119 39.8 2.1 12 mi. S of downtown Santa Barbara 5/23 4:42 am 34 14.7 119 38.3 2.3 " 5/23 5:22 am 34 57.9 116 49.0 3.5 13 mi. ENE of Barstow 5/23 6:22 am 34 58.4 116 48.4 3.3 " 5/23 6:43 am 34 58.3 116 48.7 2.1 " 5/23 6:52 am 34 58.3 116 48.6 2.0 " 5/23 7:38 am 33 4.2 116 27.5 3.5 8 mi. E of Julian 5/23 12:01 pm 34 58.3 116 48.5 3.0 13 mi. ENE of Barstow 5/23 3:13 pm 35 41.2 118 23.6 2.3 5 mi. NE of town of Lake Isabella 5/23 4:29 pm 36 22.5 120 55.5 2.8 35 mi. WNW of Coalinga 5/23 9:36 pm 35 47.8 117 38.2 4.0 12 mi. N of Ridgecrest 5/23 9:57 pm 34 22.9 118 37.9 2.4 3 mi. WSW of Valencia 5/24 1:46 am 34 16.2 119 39.7 2.0 10 mi. SSE of downtown Santa Barbara 5/24 7:41 am 36 10.0 118 4.3 2.2 8 mi. SSW of Olancha 5/24 12:05 pm 35 47.8 117 38.2 2.2 12 mi. N of Ridgecrest 5/24 12:53 pm 34 12.9 116 26.7 2.2 6 mi. N of Yucca Valley 5/24 1:58 pm 33 19.7 117 44.7 2.2 9 mi. S of Dana Point 5/24 9:29 pm 34 16.0 119 39.4 2.1 10 mi. SSE of downtown Santa Barbara 5/24 10:52 pm 33 4.4 116 27.4 2.7 8 mi. E of Julian 5/25 1:57 am 34 29.5 116 31.6 2.1 26 mi. N of Yucca Valley 5/25 12:16 pm 36 21.2 117 28.6 2.2 25 mi. SW of Stovepipe Wells 5/26 6:00 am 34 58.3 116 49.0 2.1 13 mi. ENE of Barstow 5/26 6:27 am 35 56.0 120 30.4 3.0 4 mi. WNW of Parkfield 5/26 6:47 am 34 9.7 116 26.0 2.1 3 mi. NNE of Yucca Valley 5/26 7:49 am 36 9.4 118 4.5 2.7 9 mi. SSW of Olancha 5/26 10:08 am 35 58.9 120 28.7 2.3 6 mi. NNW of Parkfield 5/26 3:00 pm 34 59.0 116 57.0 2.4 7 mi. NNE of Barstow 5/26 3:18 pm 34 58.2 116 48.5 2.0 13 mi. ENE of Barstow 5/27 10:15 am 34 22.6 118 40.5 2.0 7 mi. NNE of Simi Valley 5/27 1:00 pm 34 10.0 117 20.5 2.1 4 mi. NNE of Rialto 5/27 7:44 pm 34 16.7 116 26.8 2.0 11 mi. N of Yucca Valley 5/28 2:13 am 34 31.9 119 1.1 2.3 10 mi. NNW of Fillmore -------------------------------------------------------------