October 20, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ October 13 - 19, 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, October 13, Pacific Daylight Time, to midnight Wednesday night, October 19, Pacific Daylight Time. We recorded 298 earthquakes of M1.0 or larger this week. The largest event of the week (M4.3) occurred southeast of Ridgecrest, near the Garlock Fault, late Tuesday afternoon. It was part of a small swarm of 18 quakes, which also included a M3.5 later Tuesday evening. All but two of the 18 quakes were on Tuesday or Wednesday. The focal mechanisms for both the M4.3 and M3.5 events were strike-slip, compatible with left-lateral slip on the Garlock. Although not an extremely active fault, the Garlock has produced several other small earthquakes in the last few decades. This week's event is the same size as the previous largest event, a M4.3 that occurred in June '74. The locations are very close, too: the 1974 earthquake was within 5 kilometers of the location of this one. This week's location saw two M3's within a few months after the Landers quake of '92, but has been fairly quiet since. There were two events in the M3 range, both on Wednesday. The first was a Landers aftershock (M3.0) in the desert area north of Yucca Valley. The second was on Wednesday evening, also M3.0, near Ocotillo, along the U.S./Mexican border. We received public inquiries about two quakes this week, one of which was actually in Menlo Park's coverage area. That one was in the Morro Bay area last Thursday afternoon, M2.9. Another M2.9 was felt in the Big Bear area on Sunday morning. 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 Daylight Time listed. Table 1 ------- Date Time N Lat. W Long. Mag ------------------------------------------------------------- 10/13 12:37 am 35 29.7 120 51.8 2.6 9 mi. N of Morro Bay 10/13 3:31 am 34 10.6 116 49.5 2.1 5 mi. N of Mt. San Gorgonio 10/13 3:32 am 34 8.8 116 25.5 2.1 2 mi. NNE of Yucca Valley 10/13 6:09 am 34 17.8 116 53.1 2.4 2 mi. NW of Big Bear City 10/13 2:08 pm 34 47.3 116 18.2 2.3 35 mi. SSW of Baker 10/13 4:06 pm 35 29.9 120 51.2 2.9 9 mi. N of Morro Bay; FELT 10/13 8:24 pm 35 54.5 117 42.6 2.4 16 mi. SE of Coso Junction 10/13 10:08 pm 34 23.0 116 27.4 2.0 18 mi. N of Yucca Valley 10/13 10:25 pm 35 54.5 117 42.6 2.0 16 mi. SE of Coso Junction 10/13 11:45 pm 34 33.7 116 26.3 2.5 30 mi. N of Yucca Valley 10/13 11:55 pm 35 2.0 116 59.0 2.1 10 mi. NNE of Barstow 10/13 11:56 pm 35 2.0 116 58.8 2.1 " 10/14 5:58 am 33 59.9 116 55.3 2.0 5 mi. NNW of Banning 10/14 7:48 pm 33 54.1 118 54.9 2.5 9 mi. S of Leo Carrillo State Beach 10/15 1:46 am 35 0.8 116 57.8 2.4 9 mi. NNE of Barstow 10/15 5:58 am 34 20.4 116 28.0 2.7 15 mi. N of Yucca Valley 10/15 8:30 am 34 24.6 116 28.1 2.4 20 mi. N of Yucca Valley 10/15 8:43 am 34 2.4 117 30.9 2.4 Fontana, 2 mi. SE of the I10/I15 interchange 10/15 4:45 pm 34 37.2 118 37.8 2.3 7 mi. NNW of Castaic Lake dam 10/15 5:23 pm 33 45.1 116 50.4 2.2 7 mi. W of Idyllwild 10/15 8:25 pm 34 30.5 116 31.2 2.1 27 mi. N of Yucca Valley 10/16 7:07 am 34 7.1 117 0.3 2.1 8 mi. SE of Running Springs 10/16 9:02 am 32 32.2 115 51.8 2.0 15 mi. SSE of Ocotillo 10/16 9:29 am 34 13.8 116 45.2 2.9 6 mi. ESE of Big Bear City FELT 10/16 10:02 am 35 30.7 117 29.6 2.1 12 mi. SE of Ridgecrest 10/16 10:29 am 34 47.0 116 17.9 2.6 35 mi. SSW of Baker 10/16 2:17 pm 34 20.1 116 28.2 2.1 15 mi. N of Yucca Valley 10/16 2:22 pm 35 31.0 117 29.8 2.2 12 mi. SE of Ridgecrest 10/16 8:10 pm 34 11.5 116 49.7 2.2 5 mi. SSE of Big Bear City 10/16 10:29 pm 33 54.9 116 57.6 2.0 1 mi. SE of Beaumont 10/17 8:18 am 34 37.6 116 40.2 2.3 20 mi. NE of Lucerne Valley 10/17 1:40 pm 34 21.2 118 27.1 2.2 5 mi. N of San Fernando 10/17 10:37 pm 34 13.4 116 46.2 2.2 5 mi. ESE of Big Bear City 10/18 12:34 am 35 53.5 117 40.5 2.0 18 mi. N of Ridgecrest 10/18 12:34 am 35 40.2 118 58.9 2.2 19 mi. N of downtown Bakersfield 10/18 3:42 am 32 43.5 118 21.4 2.0 6 mi. S of San Clemente Is. 10/18 1:42 pm 34 18.1 116 29.8 2.2 12 mi. NNW of Yucca Valley 10/18 1:59 pm 33 4.2 114 59.3 2.0 33 mi. NW of Yuma, Arizona 10/18 3:11 pm 34 36.0 116 36.7 2.2 21 mi. ENE of Lucerne Valley 10/18 4:22 pm 32 39.8 115 54.3 2.0 7 mi. SE of Ocotillo 10/18 5:37 pm 34 5.8 116 26.6 2.4 1 mi. S of Yucca Valley 10/18 5:49 pm 35 30.7 117 29.6 4.3 12 mi. SE of Ridgecrest 10/18 7:49 pm 32 44.9 115 26.2 2.2 6 mi. NNE of Calexico 10/18 8:34 pm 35 30.7 117 29.5 3.5 12 mi. SE of Ridgecrest 10/18 9:55 pm 34 10.1 116 26.3 2.1 3 mi. N of Yucca Valley 10/18 10:03 pm 35 30.5 117 29.4 2.0 12 mi. SE of Ridgecrest 10/18 11:26 pm 35 29.0 119 26.8 2.1 23 mi. N of Taft 10/19 3:20 am 35 50.6 117 38.5 2.1 15 mi. N of Ridgecrest 10/19 4:28 am 34 2.2 117 13.9 2.0 3 mi. WSW of Redlands 10/19 4:35 am 35 31.9 117 29.7 2.1 11 mi. ESE of Ridgecrest 10/19 4:49 am 34 7.4 116 23.9 2.0 2 mi. E of Yucca Valley 10/19 6:14 am 34 17.1 118 27.3 2.0 Under San Fernando 10/19 6:28 am 34 16.2 118 27.8 2.0 1 mi. WSW of San Fernando 10/19 11:38 am 34 6.5 119 34.2 2.0 6 mi. NNW of Santa Cruz Is. 10/19 1:04 pm 34 27.0 116 29.9 3.0 23 mi. N of Yucca Valley 10/19 1:51 pm 35 30.7 117 29.5 2.2 12 mi. SE of Ridgecrest 10/19 7:37 pm 35 17.5 118 34.4 2.8 13 mi. NNW of Tehachapi 10/19 7:56 pm 32 43.4 115 55.7 3.0 3 mi. ESE of Ocotillo 10/19 10:34 pm 32 43.4 115 55.6 2.5 " ------------------------------------------------------------- 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.