November 22, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ November 17 - 21, 1994 Prepared by: Kate Hutton, Seismological Laboratory (kate@bombay.gps.caltech.edu) Lucy Jones, U.S. Geological Survey California Institute of Technology This document is a commentary on current seismic activity. The earthquakes discussed have been detected and processed automatically. All epicenters and magnitudes have been reviewed to exclude obvious blunders; however, they must still be considered preliminary. 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, November 17, Pacific Standard Time, to midnight Monday night, November 21, Pacific Standard Time. Because of the holiday, the Weekly Report is being porduced early this week. We recorded 206 earthquakes of M1.0 or larger during the 5-day period covered. There were two events felt this week, one aftershock each in the Landers and Northridge sequences. The week's largest event was the M4.2 Landers aftershock that was felt in Yucca Valey. It occurred on Saturday night. It was the largest Landers aftershock since a M4.9 in August 1994. Like the M7.3 mainshock and most of the aftershocks, it had a strike-slip mechanism, with right-lateral slip along a north-northwest plane. Three to five more aftershocks above M4.0 will probably occur in the Landers sequence in the next year. Although the number of aftershocks dies off with time, the ratio of small to large aftershocks stays the same. Therefore, as long as we continue to have many small aftershocks each week, we can expect to see an occasional larger one. The second largest event, and the only other one of M3 or larger, was the Northridge aftershock that occurred on Sunday night. It had a magnitude of M3.0. Otherwise, there was nothing even slightly exciting. The table 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 ------------------------------------------------------------- 11/17 12:33 am 35 33.1 120 51.7 2.2 13 mi. N of Morro Bay 11/17 12:57 am 34 20.7 118 33.8 2.5 3 mi. SW of Newhall 11/17 3:49 am 34 13.6 116 44.9 2.0 6 mi. ESE of Big Bear City 11/17 4:09 am 34 24.9 117 2.8 2.3 6 mi. WSW of Lucerne Valley 11/17 2:39 pm 34 15.3 118 28.2 2.1 2 mi. SW of San Fernando 11/18 5:26 am 34 40.1 116 29.0 2.0 30 mi. ENE of Lucerne Valley 11/18 10:14 am 36 6.6 117 51.9 2.6 4 mi. ESE of Haiwee Reservoir 11/18 3:29 pm 33 26.6 116 24.0 2.0 13 mi. N of Borrego Springs 11/18 4:38 pm 35 36.7 118 21.8 2.1 6 mi. ESE of the town of Lake Isabella 11/18 5:50 pm 34 15.6 118 36.0 2.1 4 mi. N of Canoga Park 11/18 8:43 pm 32 40.2 115 54.3 2.1 6 mi. SE of Ocotillo 11/18 9:12 pm 33 21.4 116 22.6 2.2 7 mi. N of Borrego Springs 11/18 11:54 pm 36 50.0 118 9.4 2.8 3 mi. NE of Independence 11/19 1:33 am 34 49.3 116 19.6 2.0 33 mi. SSW of Baker 11/19 10:49 am 34 9.4 116 25.4 2.4 2 mi. NNE of Yucca Valley 11/19 4:25 pm 34 0.8 116 19.2 2.6 10 mi. SE of Yucca Valley 11/19 5:43 pm 33 59.7 116 16.3 2.7 13 mi. SE of Yucca Valley 11/19 8:31 pm 34 0.7 116 19.1 4.2 10 mi. SE of Yucca Valley FELT 11/19 9:02 pm 34 1.1 116 19.2 2.0 " 11/19 11:11 pm 34 0.7 116 19.1 2.3 " 11/20 12:14 am 34 1.0 116 19.2 2.4 " 11/20 3:34 am 34 37.0 116 39.4 2.2 20 mi. NE of Lucerne Valley 11/20 5:06 am 35 3.1 117 7.5 2.3 12 mi. NNW of Barstow 11/20 8:03 am 36 53.3 118 10.7 2.7 5 mi. N of Independence 11/20 11:04 am 34 47.5 116 17.7 2.7 35 mi. SSW of Baker 11/20 3:11 pm 34 21.3 118 41.3 2.2 5 mi. NNE of Simi Valley 11/20 4:14 pm 34 1.0 116 19.5 2.0 9 mi. SE of Yucca Valley 11/20 8:14 pm 34 16.9 118 33.7 2.0 3 mi. NNW of Northridge 11/20 10:07 pm 34 15.9 118 34.1 3.0 2 mi. NW of Northridge FELT 11/21 3:24 am 32 43.5 115 55.5 2.0 4 mi. E of Ocotillo 11/21 10:48 am 36 14.1 120 48.7 2.7 26 mi. WNW of Coalinga 11/21 6:03 pm 33 30.4 117 3.4 2.1 15 mi. NW of Palomar Observatory 11/21 7:09 pm 36 7.3 118 56.5 2.2 5 mi. ENE of Porterville 11/21 7:33 pm 34 29.4 116 30.6 2.2 25 mi. N of Yucca Valley 11/21 8:56 pm 34 18.8 118 24.1 2.2 3 mi. NE of San Fernando 11/21 9:11 pm 34 0.7 116 19.4 2.0 10 mi. SE of Yucca Valley ------------------------------------------------------------- Figure 1. A map of southern California showing the earthquakes recorded during the past week by the Caltech/USGS Seismic Network. Major faults are marked, as well as the metropolitan areas of Los Angeles (L.A.), Palm Springs (P.S.), San Diego (S.D.), and Santa Barbara (S.B.). The circles denote the earthquakes, the size of the circle indicating the magnitude.