January 13, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ January 6 - 12, 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 Tuesday morning, January 6, Pacific Standard Time, to midnight Wednesday night, January 12, Pacific Standard Time. The map includes a virtually complete set of earthquakes of M2.0 or larger, plus many smaller ones that happen to have made it through the data processing. There are 320 this time. The week's largest event, and probably the most exciting from the public point of view, was the M3.7 just offshore of Venice Beach on Sunday afternoon. (We hope no-one dropped a barbell on their toe!) It was widely felt in west L.A. and the San Fernando Valley. As the table shows, there was one foreshock and a number of aftershocks, some of which were also felt. In fact, the staff was amazed at the sensitivity of West Side residents, many of them apparently news reporters, to the small tremors! The second largest member of the sequence was a M3.5 on Tuesday evening. Technically, the Santa Monica sequence is a swarm, and not a mainshock/aftershock sequence, because the largest 2 events were of similar size, and because the earthquake rate stayed about constant for 2 or 3 days, rather than decaying with time as after- shocks normally do. The quakes occurred on an offshore thrust fault, with a nearly east-west stike and possibly a steep dip to the south. Because precise location of earthquakes in a noisy bowl of mud like the L.A. Basin is very difficult, we are unsure of the depth. However, they must be within a few kilometers of the surface, for people to be feeling M2.2's. A map showing the details of the sequence is included. On Friday evening, there was a Landers aftershock with a magnitude of M3.5. It occurred in a sparsely populated area NE of Lucerne Valley and was not reported felt. The table lists the quakes that were M2.0 or larger in the central part of the coverage area. Only M2.5 and larger events are listed for south of the U.S./Mexico border, and for the Coalinga/Parkfield area. For more information on the latter, see the Northern California Report issued by the U.S.G.S. in Menlo Park. Times are local times; if you want Greenwich Mean Time, add 8 hrs, to the Pacific Standard Time listed. Table 1 ------- Date Time N Lat. W Long. Mag ------------------------------------------------------------- 1/6 12:53 am 34 25.2 116 28.6 2.1 20 mi. N of Yucca Valley 1/6 7:15 am 34 16.8 116 46.2 2.8 4 mi. ENE of Big Bear City 1/6 8:23 am 34 55.0 116 55.5 2.3 5 mi. ENE of Barstow 1/6 11:21 am 34 37.0 117 16.0 2.1 5 mi. NNE of Victorville 1/6 1:44 pm 33 48.4 120 19.5 2.2 15 mi. S of San Miguel Is. 1/6 7:53 pm 36 1.3 120 0.0 3.4 21 mi. ESE of Coalinga 1/7 12:24 am 34 15.6 117 3.0 2.1 4 mi. NE of Running Springs 1/7 5:01 am 35 8.7 119 6.0 2.1 12 mi. NW of the I5/99 interchange 1/7 5:33 am 32 19.5 115 13.2 2.8 28 mi. SE of Calexico 1/7 7:21 am 36 10.2 117 56.1 2.1 2 mi. NNE of south end of Haiwee Reservoir 1/7 7:47 am 34 34.6 116 36.3 2.3 21 mi. ENE of Lucerne Valley 1/7 8:13 am 34 22.0 116 27.3 2.0 17 mi. N of Yucca Valley 1/7 11:22 am 34 20.0 116 27.1 2.1 14 mi. N of Yucca Valley 1/7 1:04 pm 34 52.2 116 39.3 2.1 20 mi. E of Barstow 1/7 5:42 pm 34 21.2 116 27.9 2.1 16 mi. N of Yucca Valley 1/7 11:06 pm 34 40.3 116 42.0 3.5 20 mi. NE of Lucerne Valley 1/8 2:13 am 34 40.0 116 42.1 2.1 " 1/8 2:16 am 34 40.5 116 42.3 3.0 " 1/8 3:31 am 35 59.6 118 2.3 2.0 6 mi. SW of Coso Junction 1/8 5:02 am 34 11.0 117 22.9 2.0 2 mi. SE of Glen Helen Re- gional Park, Cajon Pass 1/8 6:09 am 35 27.5 118 2.9 2.5 24 mi. WSW of Ridgecrest 1/8 7:08 am 34 2.1 116 22.4 2.0 7 mi. SE of Yucca Valley 1/8 4:38 pm 35 58.5 117 40.3 2.2 16 mi. ESE of Coso Junction 1/9 2:40 am 34 40.0 116 42.2 2.1 20 mi. NE of Lucerne Valley 1/9 5:43 am 33 55.5 118 34.6 2.5 8 mi. SW of Santa Monica 1/9 11:03 am 32 59.2 117 46.7 2.2 27 mi. WSW of Oceanside 1/9 1:49 pm 34 9.0 116 41.4 2.3 8 mi. ENE of Mt. San Gor- gonio 1/9 2:34 pm 33 22.7 116 24.3 2.0 8 mi. NNW of Borrego Springs 1/9 3:00 pm 33 59.3 118 30.2 3.7 2 mi. SSW of Santa Monica Widely FELT in West L.A. area 1/9 3:50 pm 34 0.3 116 50.7 2.0 5 mi. NNE of Banning 1/9 3:58 pm 35 58.4 117 40.1 2.0 16 mi. ESE of Coso Junction 1/9 6:33 pm 34 7.0 116 52.3 2.1 2 mi. WNW of Mt. San Gor- gonio 1/9 6:34 pm 34 6.8 116 52.3 2.1 " 1/9 6:34 pm 34 6.9 116 52.2 2.2 " 1/9 10:12 pm 33 59.6 118 29.5 3.1 1 mi. S of Santa Monica; FELT 1/9 11:27 pm 33 35.3 118 20.7 2.0 8 mi. SSW of Pt. Fermin, San Pedro 1/9 11:32 pm 34 2.2 116 19.3 2.2 9 mi. SE of Yucca Valley 1/10 5:07 am 35 33.0 120 49.1 2.8 9 mi. SW of Paso Robles 1/10 6:55 am 34 6.1 117 56.0 2.0 4 mi. NE of the I10/I605 interchange, Irwindale 1/10 10:55 am 33 60.0 118 29.4 2.2 1 mi. S of Santa Monica; FELT 1/10 12:47 pm 33 59.3 118 30.2 2.5 2 mi. SSW of Santa Monica 1/10 3:21 pm 33 49.4 115 39.5 2.1 10 mi. W of Eagle Mtn. 1/10 3:40 pm 33 11.8 115 33.5 2.1 3 mi. SW of Niland 1/10 4:59 pm 35 29.3 118 27.3 2.4 10 mi. S of the town of Lake Isabella 1/10 6:11 pm 34 15.4 116 26.4 2.0 9 mi. N of Yucca Valley 1/10 8:38 pm 35 2.0 116 58.3 2.4 10 mi. NNE of Barstow 1/11 1:38 am 34 23.2 117 1.0 2.0 5 mi. SW of Lucerne Valley 1/11 2:33 am 34 37.0 116 39.2 2.5 20 mi. NE of Lucerne Valley 1/11 2:33 am 34 16.5 116 46.7 2.6 4 mi. E of Big Bear City 1/11 12:45 pm 34 2.1 116 21.6 2.0 7 mi. SE of Yucca Valley 1/11 3:13 pm 34 21.7 116 27.2 2.2 16 mi. N of Yucca Valley 1/11 7:26 pm 34 26.4 116 29.8 2.0 22 mi. N of Yucca Valley 1/11 9:08 pm 33 59.3 118 30.0 2.2 2 mi. SSW of Santa Monica FELT 1/11 11:27 pm 33 59.0 118 30.3 3.5 2 mi. SSW of Santa Monica FELT 1/12 12:23 am 33 59.4 118 31.2 2.1 2 mi. SW of Santa Monica 1/12 1:41 am 34 28.8 116 30.1 2.3 25 mi. N of Yucca Valley 1/12 10:41 am 33 59.1 118 29.4 2.0 2 mi. S of Santa Monica 1/12 10:45 am 34 26.6 116 28.6 2.1 22 mi. N of Yucca Valley 1/12 11:03 am 32 41.7 115 55.8 2.2 4 mi. SE of Ocotillo 1/12 11:26 am 35 20.8 116 24.6 2.4 19 mi. WNW of Baker 1/12 11:28 am 33 59.1 118 30.5 3.1 2 mi. SSW of Santa Monica FELT 1/12 5:06 pm 36 13.1 117 33.4 2.3 9 mi. SSW of Panamint Springs 1/12 5:16 pm 36 2.5 117 47.5 2.3 8 mi. E of Coso Junction 1/12 7:44 pm 34 37.6 116 39.8 2.1 20 mi. NE of Lucerne Valley ------------------------------------------------------------- Figure. 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.