April 14, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ April 7 - 13, 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, April 7, Pacific Daylight Time, to midnight Wednesday night, April 13, Pacific Daylight Time. There are 432 this week. The week was somewhat dull compared to last week. There were three quakes above M3, only one of which was a Northridge aftershock. The aftershock was a M3.2 in the Newhall area late Tuesday afternoon. The others were: a M3.6 near Fillmore on Friday, fairly widely felt, and a M3.0 in the Lake Arrowhead area, also on Friday. All three of these were felt. The Northridge aftershock zone is still expected to produce an average of three or four M3 or greater quakes per week, so we were a little under quota this week. The Fillmore quake was near, but not in, the Northridge aftershock zone. It had a thrust focal mechanism and was located such that it could have occurred on the San Cayatano fault. Since the Northridge earthquake, we have noticed as slight increase in activity near this fault (see, in particular, the Feb. 11 Weekly Report). The area has always been fairly active, however, so this activity is not considered anomalous. Some other very small quakes in the L.A. area escaped public notice, including: a M2.0 near Mt. Wilson, just south of the now-dead aftershock sequence of the '91 Sierra Madre quake; a M2.0 just north of La Brea tar pits, and a M1.5 under the bend in the 110 freeway in South Pasadena. These, along with the Fillmore quake, are sufficiently removed from the Northridge aftershocks to be considered independent quakes. All the rest was fairly ordinary. The table lists the quakes 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 ------------------------------------------------------------- 4/7 12:08 am 34 22.9 118 37.9 2.4 3 mi. SW of Magic Mtn. 4/7 2:55 am 34 16.2 118 38.9 2.4 3 mi. E of Simi Valley 4/7 5:17 am 34 56.0 115 35.4 2.2 35 mi. SE of Baker 4/7 6:31 am 34 19.8 116 38.9 2.0 12 mi. ENE of Big Bear City 4/7 6:35 am 34 23.4 118 35.2 2.4 2 mi. S of Magic Mtn. 4/7 7:15 am 34 13.5 117 57.5 2.0 5 mi. E of Mt. Wilson Observatory 4/7 8:32 am 34 19.6 116 28.1 2.6 14 mi. N of Yucca Valley 4/7 9:09 am 34 9.0 116 42.3 2.7 7 mi. ENE of Mt. San Gorgonio 4/7 11:24 am 34 59.0 116 56.8 2.9 7 mi. NNE of Barstow 4/7 11:28 am 33 15.3 116 1.2 2.7 3 mi. WSW of Salton City 4/7 11:48 am 34 57.8 116 56.2 2.7 7 mi. NE of Barstow 4/7 8:38 pm 34 20.5 116 28.5 2.0 15 mi. N of Yucca Valley 4/7 11:00 pm 34 2.5 117 15.1 2.9 1 mi. S of Loma Linda; FELT 4/8 2:06 am 34 21.1 118 31.5 2.0 1 mi. S of Newhall 4/8 5:54 am 33 46.5 116 8.1 2.1 6 mi. NE of Indio 4/8 6:45 am 34 19.5 118 26.6 2.3 2 mi. N of San Fernando 4/8 7:36 am 34 15.1 118 28.3 2.6 2 mi. SW of San Fernando 4/8 10:15 am 34 18.3 118 27.2 2.8 1 mi. NNW of San Fernando 4/8 10:53 am 34 27.9 118 57.3 3.6 5 mi. NNW of Fillmore; FELT 4/8 2:44 pm 35 32.8 118 29.7 2.0 6 mi. SSW of the town of Lake Isabella 4/8 3:17 pm 34 27.3 116 29.7 2.0 23 mi. N of Yucca Valley 4/8 4:57 pm 34 11.4 117 5.7 3.0 1 mi. SSE of Running Springs FELT 4/8 6:26 pm 34 59.2 116 57.4 2.6 7 mi. NNE of Barstow 4/8 7:51 pm 34 20.7 116 28.0 2.3 15 mi. N of Yucca Valley 4/8 7:53 pm 34 20.5 116 28.4 2.2 " 4/8 10:24 pm 33 10.4 115 37.2 2.2 6 mi. WNW of Calipatria 4/8 10:47 pm 36 8.4 118 7.3 2.5 9 mi. W of south end of Haiwee Reservoir 4/9 5:26 am 33 27.6 118 6.2 2.0 14 mi. SW of Newport Beach 4/9 5:29 am 34 15.5 118 40.8 2.6 2 mi. SE of Simi Valley 4/9 6:10 am 34 24.1 118 38.0 2.6 2 mi. WSW of Magic Mtn. 4/9 8:15 am 34 17.3 118 27.6 2.4 1 mi. WNW of San Fernando 4/9 12:15 pm 34 22.0 118 39.4 2.9 5 mi. SW of Magic Mtn.; FELT 4/9 12:17 pm 34 22.0 118 39.3 2.4 " 4/9 2:18 pm 34 16.3 118 26.4 2.6 Under San Fernando 4/9 2:37 pm 34 54.2 116 41.8 2.4 18 mi. E of Barstow 4/9 5:19 pm 33 28.7 116 29.7 2.1 11 mi. ESE of Anza 4/10 4:25 am 33 28.5 116 27.9 2.2 13 mi. ESE of Anza 4/10 8:24 am 34 4.4 118 21.6 2.0 1 mi. N of La Brea tar pits 4/10 9:01 am 34 20.2 118 28.6 2.6 4 mi. SE of Newhall 4/10 11:14 am 34 38.2 116 39.6 2.0 21 mi. NE of Lucerne Valley 4/10 2:02 pm 34 16.8 118 28.0 2.0 1 mi. W of San Fernando 4/10 8:00 pm 34 33.7 119 10.6 2.9 8 mi. NNE of Ojai 4/10 9:08 pm 34 19.4 118 28.9 2.2 3 mi. NW of San Fernando 4/11 2:46 am 34 38.1 116 31.2 2.3 27 mi. ENE of Lucerne Valley 4/11 8:36 am 34 9.1 116 25.0 2.8 2 mi. NE of Yucca Valley 4/11 10:41 am 34 9.0 116 25.0 2.3 " 4/11 6:54 pm 34 7.0 116 55.2 2.5 5 mi. WNW of Mt. San Gorgonio 4/12 2:18 am 34 57.0 116 53.2 2.1 8 mi. ENE of Barstow 4/12 8:12 am 34 19.0 118 27.5 2.3 2 mi. NNW of San Fernando 4/12 10:37 am 34 22.2 116 27.1 2.4 17 mi. N of Yucca Valley 4/12 12:45 pm 34 42.6 116 52.8 2.0 14 mi. SSE of Barstow 4/12 4:27 pm 34 25.0 116 28.0 2.1 20 mi. N of Yucca Valley 4/12 5:43 pm 34 36.9 116 36.7 2.6 22 mi. ENE of Lucerne Valley 4/12 6:57 pm 34 20.0 118 35.6 3.2 4 mi. SW of Newhall; FELT 4/12 10:59 pm 34 18.3 118 26.1 2.0 1 mi. N of San Fernando 4/13 4:18 am 34 22.1 118 30.8 2.8 1 mi. SE of Newhall; FELT 4/13 5:15 am 34 1.9 116 13.3 2.0 12 mi. SW of Twentynine Palms 4/13 8:06 am 34 21.4 118 30.5 2.0 1 mi. SE of Newhall 4/13 8:07 am 34 25.0 116 28.6 2.4 20 mi. N of Yucca Valley 4/13 8:29 am 34 16.9 118 28.9 2.6 2 mi. W of San Fernando 4/13 2:42 pm 33 15.1 116 1.0 2.2 3 mi. WSW of Salton City 4/13 7:49 pm 34 29.5 118 42.3 2.5 6 mi. WSW of Castaic Lake dam 4/13 11:42 pm 34 19.0 118 33.1 2.6 4 mi. SSW of Newhall ------------------------------------------------------------- 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.