December 16, 1993 Weekly Earthquake Report for Southern California ------------------------------------------------ December 9 - 15, 1993 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 9, Pacific Standard Time, to midnight Wednesday night, December 15, 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 357 this time. It was a fairly uneventful week. There were four M3+ quakes, two of which were well inside the network. None of them were felt by the public. The week's largest was a M3.3 near Redlands very early Friday morning. The two events which were felt were: a Ridgecrest quake at a more reasonable hour on Friday morning (M2.8), and a Big Bear quake (aftershock of June 28, 1992) early Monday morning. The swarm of earthquakes in northern Baja California is continuing. The largest earthquake this week was M3.0. The geology of this region is complex, involving the transference of plate motion from the strike-slip faults of southern California to the ocean ridge of the Gulf of California. In general, the region is characterized by alternating strike-slip faults (such as the Imperial Valley and Superstition Hills faults) and extensional regions such as the Brawley seismic zone. This swarm, however, is located between the ends of the Cerro Prieto and Laguna Salada faults, a "left step" rather than the usual "right step". This implies a more compressional environment. We do not have adequate focal mechanisms this far south of our stations to determine if this is indeed the case. 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 ------------------------------------------------------------- 12/9 1:11 am 32 21.3 115 21.0 2.9 23 mi. SSE of Calexico 12/9 3:23 am 32 39.5 115 54.3 2.0 7 mi. SE of Ocotillo 12/9 5:23 am 34 29.5 118 41.0 2.4 5 mi. WSW of Castaic Lake dam 12/9 5:59 am 36 15.3 120 22.0 2.5 8 mi. N of Coalinga 12/9 7:40 am 34 30.1 116 31.4 2.1 26 mi. N of Yucca Valley 12/9 8:07 am 34 0.7 116 19.1 2.1 10 mi. SE of Yucca Valley 12/9 8:08 am 34 59.3 116 57.6 2.1 7 mi. NNE of Barstow 12/9 12:21 pm 34 13.4 116 26.1 2.1 7 mi. N of Yucca Valley 12/9 12:21 pm 34 13.3 116 26.3 2.1 " 12/9 2:09 pm 32 21.9 115 20.2 3.0 22 mi. SSE of Calexico 12/9 7:37 pm 36 8.1 118 4.2 2.2 6 mi. W of south end of Haiwee Reservoir 12/9 7:37 pm 32 34.3 117 40.9 2.5 31 mi. SW of La Jolla 12/9 9:47 pm 35 13.7 120 42.3 2.0 4 mi. SW of San Luis Obispo 12/10 2:06 am 35 38.9 117 38.2 2.7 2 mi. NE of Ridgecrest 12/10 2:10 am 34 1.1 117 6.5 3.3 4 mi. ESE of Redlands 12/10 2:14 am 35 38.7 117 38.2 2.1 2 mi. NE of Ridgecrest 12/10 2:28 am 34 16.3 116 43.3 2.2 7 mi. E of Big Bear City 12/10 5:51 am 34 14.2 119 29.9 2.4 11 mi. S of Carpinteria 12/10 7:06 am 35 38.9 117 38.3 2.8 2 mi. NE of Ridgecrest; FELT 12/10 7:41 am 34 36.4 116 38.1 2.0 20 mi. ENE of Lucerne Valley 12/10 7:44 am 32 23.7 115 19.5 2.8 21 mi. SSE of Calexico 12/10 8:58 am 35 1.0 116 57.8 2.2 9 mi. NNE of Barstow 12/10 10:40 am 34 37.3 116 33.0 2.1 25 mi. ENE of Lucerne Valley 12/10 1:12 pm 32 50.8 116 5.7 2.0 9 mi. NW of Ocotillo 12/10 2:00 pm 34 36.3 116 37.0 2.2 21 mi. ENE of Lucerne Valley 12/10 3:51 pm 33 48.3 118 9.1 2.1 2 mi. NNE of downtown Long Beach 12/10 4:07 pm 33 59.1 116 47.9 2.2 4 mi. N of Cabazon 12/10 4:19 pm 34 34.3 116 41.6 2.2 16 mi. ENE of Lucerne Valley 12/10 8:11 pm 33 58.9 117 1.0 2.0 4 mi. NNW of Beaumont 12/10 9:37 pm 34 8.7 116 50.3 2.0 3 mi. NNW of Mt. San Gorgonio 12/10 10:31 pm 35 39.0 117 37.9 2.0 2 mi. NE of Ridgecrest 12/10 10:51 pm 34 6.1 116 59.7 2.0 9 mi. SE of Running Springs 12/11 6:05 am 36 10.3 118 1.3 2.2 4 mi. WNW of south end of Haiwee Reservoir 12/11 7:59 am 36 9.2 118 1.7 2.8 " 12/11 8:01 am 34 23.4 116 27.9 2.0 18 mi. N of Yucca Valley 12/11 10:57 am 32 22.2 115 20.9 2.7 22 mi. SSE of Calexico 12/11 11:54 am 32 24.6 115 20.0 2.6 " 12/11 1:42 pm 33 3.6 116 28.5 2.0 7 mi. E of Julian 12/11 4:45 pm 35 28.2 119 58.8 2.6 8 mi. N of Simmler 12/11 6:25 pm 34 22.8 116 27.4 2.1 18 mi. N of Yucca Valley 12/12 12:41 am 35 20.4 118 33.0 2.0 15 mi. NNW of Tehachapi 12/12 6:55 am 35 39.0 117 38.0 2.6 2 mi. NE of Ridgecrest 12/12 7:01 am 35 38.8 117 38.0 2.0 " 12/12 7:17 am 35 4.3 119 1.2 2.0 5 mi. NW of the I5/99 interchange 12/12 7:45 am 33 56.9 116 20.5 2.4 9 mi. E of Desert Hot Springs 12/12 11:35 am 34 22.4 116 27.3 2.0 17 mi. N of Yucca Valley 12/12 3:00 pm 32 26.6 115 19.7 2.8 18 mi. SSE of Calexico 12/12 7:25 pm 34 28.8 116 30.6 2.1 25 mi. N of Yucca Valley 12/13 2:46 am 35 20.5 118 33.1 2.2 15 mi. NNW of Tehachapi 12/13 3:00 am 35 39.0 117 38.0 2.2 2 mi. NE of Ridgecrest 12/13 6:00 am 34 18.4 117 0.6 2.9 7 mi. NW of town of Big Bear Lake; FELT 12/13 6:30 am 34 21.0 116 28.1 2.1 16 mi. N of Yucca Valley 12/13 3:25 pm 36 56.2 118 8.3 2.1 9 mi. NNE of Independence 12/13 3:35 pm 36 55.5 118 9.9 2.2 " 12/13 4:21 pm 36 56.0 118 9.3 2.3 " 12/13 5:42 pm 34 4.4 117 5.6 2.1 4 mi. ENE of Redlands 12/13 9:46 pm 34 20.1 116 28.3 2.1 15 mi. N of Yucca Valley 12/13 10:52 pm 36 25.2 117 52.7 2.8 11 mi. NE of Olancha 12/14 1:26 am 33 32.0 117 1.6 2.0 15 mi. SSW of Hemet 12/14 3:39 am 34 37.9 116 40.0 2.3 20 mi. NE of Lucerne Valley 12/14 7:56 am 35 59.5 117 41.5 2.2 14 mi. ESE of Coso Junction 12/14 10:04 am 36 4.6 117 43.2 3.2 12 mi. E of Coso Junction 12/14 7:01 pm 34 10.7 116 49.6 2.0 5 mi. N of Mt. San Gorgonio 12/15 1:23 am 34 26.5 116 30.4 2.4 22 mi. N of Yucca Valley 12/15 1:55 am 34 18.8 116 26.3 2.1 13 mi. N of Yucca Valley 12/15 2:26 am 36 11.4 120 10.8 3.0 10 mi. ENE of Coalinga 12/15 4:40 am 34 1.1 117 6.6 2.0 4 mi. ESE of Redlands 12/15 5:14 am 34 22.6 116 27.9 2.0 17 mi. N of Yucca Valley 12/15 1:24 pm 34 3.4 116 26.3 2.5 4 mi. S of Yucca Valley 12/15 2:47 pm 34 37.7 116 40.0 2.1 20 mi. NE of Lucerne Valley 12/15 4:23 pm 34 56.5 120 50.4 2.6 25 mi. SSW of San Luis Obispo 12/15 10:54 pm 34 7.1 116 38.4 2.2 10 mi. E of Mt. San Gorgonio ------------------------------------------------------------- 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.