January 5, 1995 Weekly Earthquake Report for Southern California ------------------------------------------------ December 29, 1994 - January 4, 1995 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, December 29, 1994, Pacific Standard Time, to midnight Wednesday night, January 4, 1995, Pacific Standard Time. We recorded 269 earthquakes of M1.0 or larger during the 7-day period covered. It was another quiet week. There were only two M3+ quakes in our monitoring area, excluding the two in northern Baja. The largest event was a M3.3 Northridge aftershock early Friday morning. It was felt, as was a much smaller event (M2.6) yesterday (Wednesday) evening. The other M3+ was in the Coso Range east of Haiwee Reservoir: a M3.0 on Friday morning. The latter was part of a small swarm, which is a common occurence in the Coso area. With the New Year, comes the quarterly statistical summary. 1994 was an active year, with a total of 27,349 quakes recorded (all magnitudes). This is between twice and three times what a "quiet" year would be. 556 of these were M3.0 or larger, the largest one being, of course, Mw6.7 (the Northridge earthquake). As of the end of the year, the breakdown by magnitude of the Northridge sequence itself was as follows: All events 11,031 3.0 - 3.9 367 4.0 - 4.9 48 5.0 and up 9 A similar breakdown for the Landers sequence (April 23, 1992 through the end of 1994) was as follows: All events 45,000+ 3.0 - 3.9 1,474 4.0 - 4.9 158 5.0 and up 21 We still aren't finished with the data processing, hence the lower limit on the total number of events. As for the coming year, statistically speaking, the Northridge sequence should produce about 17 M3's, about two M4's, and has about a 25% chance of producing another M5. The expected number of aftershocks for the Landers/Big Bear sequence is similar: about 32 M3's, about 3 M4's, and about a 25% chance of another M5. By comparison, the chance of an independent M5+ earthquake somewhere in southern California (including all the sparsely populated areas) is about 80%. 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 ------------------------------------------------------------- 12/29 9:16 am 33 47.5 117 6.0 2.4 8 mi. WNW of Hemet 12/29 9:45 am 34 19.3 118 46.2 2.0 4 mi. NW of Simi Valley 12/29 10:45 am 34 6.3 116 44.7 2.2 4 mi. E of Mt. San Gorgonio 12/29 1:57 pm 34 20.0 118 49.9 2.0 6 mi. SE of Fillmore 12/29 3:03 pm 33 46.0 116 8.8 2.2 5 mi. NE of Indio 12/29 5:37 pm 34 11.7 116 51.5 2.3 4 mi. S of Big Bear City 12/29 6:22 pm 34 19.5 118 28.4 2.1 3 mi. NNW of San Fernando 12/30 2:03 am 34 19.1 118 24.3 3.3 3 mi. NE of San Fernando; FELT 12/30 7:21 am 34 44.3 120 7.8 2.0 9 mi. N of Solvang 12/30 7:24 am 34 19.4 118 28.1 2.0 3 mi. NNW of San Fernando 12/30 8:22 am 36 7.6 117 50.3 3.0 5 mi. E of Haiwee Reservoir 12/30 8:25 am 36 7.2 117 50.6 2.5 " 12/30 10:08 am 34 21.5 118 39.2 2.2 5 mi. SW of Magic Mtn. 12/30 12:40 pm 36 7.4 117 49.6 2.2 5 mi. E of Haiwee Reservoir 12/30 12:56 pm 36 7.2 117 50.4 2.1 " 12/30 4:07 pm 32 21.9 115 21.6 3.6 22 mi. SSE of Calexico 12/31 1:39 am 34 47.5 116 17.8 2.0 35 mi. SSW of Baker 12/31 3:51 am 34 23.5 119 22.0 2.2 8 mi. NNW of Ventura 12/31 7:21 am 34 27.9 119 21.6 2.7 6 mi. WNW of Ojai 12/31 5:01 pm 33 43.6 118 49.7 2.2 18 mi. S of Pt. Dume 12/31 7:27 pm 34 23.6 119 21.5 2.1 7 mi. WSW of Ojai 1/1 6:05 am 34 15.7 116 27.1 2.1 9 mi. N of Yucca Valley 1/1 7:13 am 34 9.5 116 26.2 2.0 2 mi. N of Yucca Valley 1/1 1:45 pm 33 55.8 117 54.8 2.2 1 mi. NW of Brea 1/1 3:41 pm 33 0.8 116 22.2 2.0 14 mi. ESE of Julian 1/1 8:04 pm 34 14.9 116 25.9 2.2 9 mi. N of Yucca Valley 1/2 12:55 am 35 2.4 116 59.6 2.0 10 mi. N of Barstow 1/2 3:32 am 32 8.6 115 2.7 3.2 44 mi. SE of Calexico 1/2 7:49 am 34 16.1 118 27.6 2.2 1 mi. SW of San Fernando 1/2 7:00 pm 34 0.8 116 19.3 2.3 10 mi. SE of Yucca Valley 1/2 7:23 pm 34 16.2 118 27.9 2.1 1 mi. WSW of San Fernando 1/3 7:37 am 32 16.1 115 19.5 2.6 29 mi. SSE of Calexico 1/3 8:03 am 34 23.9 119 22.3 2.6 7 mi. WSW of Ojai 1/3 4:26 pm 34 27.6 116 31.1 2.9 24 mi. N of Yucca Valley 1/3 6:23 pm 35 2.1 116 60.0 2.3 10 mi. N of Barstow 1/3 6:30 pm 35 59.9 117 47.8 2.6 9 mi. ESE of Coso Junction 1/3 8:05 pm 33 38.9 118 33.5 2.3 11 mi. SW of Palos Verdes Point 1/3 8:09 pm 34 14.6 118 33.4 2.6 2 mi. NW of Northridge, FELT ------------------------------------------------------------- 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.