SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey October 24, 1996 Weekly Earthquake Report for Southern California ------------------------------------------------ October 17 - 24, 1996 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, October 17, Universal Time (ie. GMT), to midnight Wednesday night, October 24, Universal Time. In local time, the period of coverage is from 5 p.m., October 16, Pacific Daylight Time, to 5 p.m., October 24, Pacific Daylight Time. We detected and processed 302 earthquakes during the seven-day period covered. One reason that the weekly total is higher, than it has been, this week and the last two week is this: due to a bug still in our new software somewhere, mining blasts are still included. They usually are not. The seismicity was a little bit higher this week than we have been seeing over the past few weeks. There were two M4+ earthquakes. The first occurred late Saturday afternoon in the desert north of Yucca Valley, and had a magnitude of 4.1. Although this location is off the main trace of the Landers (June 28, 1992, Mw7.3) fault rupture, it is a spot where early aftershocks, including a M5.4 during the first week of the sequence, did occur. We are, therefore, counting this quake as a Landers aftershock. The aftershocks at this location may be associated with the Pisgah fault. This week's focal mechanism was strike- slip, consistent with motion on the Pisgah. The quake was felt. The second one was not an aftershock of any of our recent mainshocks, although there have also been earthquakes at the same spot before. This one (M4.2) happened on Wednesday (yesterday) afternoon in the Ojai area, and produced a handful of aftershocks of its own. It occurred about 11 miles below the surface and had a thrust focal mechanism. It and its largest aftershocks were felt in Ojai. Also of interest was a M3.3 the previous Wednesday evening near the Garlock fault south of Ridgecrest. This focal mechanism was mostly strike-slip, consistent with the Garlock fault. We did not receive any felt reports on it. 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 ------------------------------------------------------------- 10/16 8:19 pm 35 25.7 117 44.9 3.3 14 mi. SSW of Ridgecrest 10/17 4:46 am 33 40.5 116 44.8 2.0 5 mi. SSW of Idyllwild 10/17 2:21 pm 33 53.4 116 9.3 2.3 12 mi. NNE of Indio 10/17 3:34 pm 33 59.8 116 46.4 2.8 5 mi. N of Cabazon 10/17 4:25 pm 34 14.1 118 34.8 2.3 1 mi. SE of Chatsworth 10/17 7:31 pm 34 1.2 116 59.7 2.0 2 mi. ESE of Yucaipa 10/18 2:20 am 33 46.3 116 6.7 2.1 7 mi. ENE of Indio 10/18 2:45 pm 33 11.4 115 36.1 3.0 2 mi. ENE of Obsidian Butte 10/18 2:45 pm 33 11.4 115 35.9 2.8 " 10/18 9:24 pm 34 32.4 119 46.2 2.3 7 mi. NNE of Goleta 10/19 12:01 am 32 38.4 115 55.3 2.2 7 mi. SSE of Ocotillo 10/19 1:35 am 33 45.2 116 0.8 2.0 13 mi. NNE of Mecca 10/19 1:41 am 34 0.4 116 18.6 2.1 8 mi. S of Joshua Tree 10/19 2:34 pm 36 18.4 117 59.4 2.1 1 mi. NNE of Olancha 10/19 5:17 pm 34 36.3 116 16.7 4.1 31 mi. N of Joshua Tree 10/19 7:01 pm 34 35.5 116 16.0 2.0 " 10/19 7:56 pm 34 35.9 116 16.4 2.1 " 10/20 2:25 am 34 14.6 117 5.8 2.0 2 mi. N of Running Springs 10/20 2:26 am 34 14.8 117 5.8 2.0 " 10/21 12:09 am 34 36.1 116 16.7 2.4 32 mi. N of Joshua Tree 10/21 1:17 am 35 59.1 117 54.8 2.6 4 mi. SSE of Coso Junction 10/21 3:49 am 35 45.9 117 37.5 2.4 10 mi. NNE of Ridgecrest 10/21 7:44 am 34 21.9 116 27.6 2.3 17 mi. N of Yucca Valley 10/21 9:41 am 33 51.3 116 59.0 2.1 5 mi. S of Beaumont 10/21 11:30 am 34 9.3 116 25.3 2.0 2 mi. NNE of Yucca Valley 10/21 12:27 pm 34 1.1 116 53.4 2.7 6 mi. N of Banning 10/21 1:15 pm 33 17.8 117 52.8 2.1 14 mi. SW of Dana Point 10/21 10:58 pm 34 12.0 116 48.3 2.4 5 mi. SSE of Big Bear City 10/22 12:04 am 34 16.2 118 25.5 2.2 1 mi. SE of Pacoima 10/22 1:17 am 34 22.9 116 27.4 2.0 18 mi. N of Yucca Valley 10/22 3:26 am 34 22.9 116 27.4 2.0 " 10/22 5:01 am 34 23.0 116 27.2 2.1 " 10/22 11:38 am 34 22.8 116 27.5 2.4 " 10/22 4:56 pm 35 40.3 119 10.1 2.3 22 mi. NNW of Bakersfield 10/22 11:15 pm 32 59.7 117 45.6 2.1 25 mi. WSW of Oceanside 10/23 12:52 am 34 21.5 118 39.2 2.1 5 mi. WSW of Valencia 10/23 2:38 pm 34 0.8 116 19.1 2.2 8 mi. S of Joshua Tree 10/23 3:09 pm 34 29.3 119 22.0 4.2 7 mi. WNW of Ojai 10/23 3:14 pm 34 29.4 119 22.9 2.1 " 10/23 3:27 pm 34 29.7 119 22.3 3.0 " 10/23 3:34 pm 34 29.4 119 22.6 2.5 " 10/23 4:06 pm 34 29.1 119 21.8 2.4 " 10/23 4:18 pm 34 28.8 119 22.1 3.6 " 10/23 4:58 pm 34 29.5 119 22.6 2.3 " -------------------------------------------------------------