December 21, 1993 Weekly Earthquake Report for Southern California ------------------------------------------------ December 16 - 20, 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 16, Pacific Standard Time, to midnight Monday night, December 20, Pacific Standard Time. The Weekly Report is being issued early this week because of the Holidays. 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 245 this time. There were no quakes reported felt this time. The swarm in Mexico continued, including one M4.0 this week, on Monday morning. That one was the week's largest. The largest one inside our true coverage area was the M3.4 off Catalina Island on Friday morning. In fact, a fairly unusual lineation of quakes occurred offshore, between the location of the 1986 Oceanside quake (ML5.3) and Catalina Island, late last week and over the weekend. This lineation is parallel to the trend of our major strike-slip faults, and has shown up in past seismicity. All this week's quakes were small, so no anxiety seems warranted. Also somewhat unusual is the pair of quakes in the Carrizo Plain, southeast of Simmler. They were M2.0 and M1.7, and occurred on Friday. They are on a segment of the San Andreas Fault which is normally quiet. Again, however, they were small and haven't provoked any anxiety. 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 ------------------------------------------------------------- 12/16 7:49 am 33 28.3 118 17.8 2.1 8 mi. N of Avalon, Catalina Island 12/16 12:49 pm 33 27.4 118 16.9 2.0 " 12/16 1:20 pm 33 1.5 117 46.4 2.4 25 mi. WSW of Oceanside 12/16 1:33 pm 34 58.3 116 57.1 2.0 7 mi. NE of Barstow 12/16 3:10 pm 33 27.1 118 15.9 2.5 8 mi. NNE of Avalon, Catalina Island 12/16 3:11 pm 33 27.7 118 17.0 2.3 " 12/16 3:23 pm 33 24.9 118 16.5 2.1 5 mi. NNE of Avalon, Catalina Island 12/16 4:52 pm 34 22.6 116 27.2 2.0 17 mi. N of Yucca Valley 12/16 6:56 pm 33 25.3 118 16.9 2.3 5 mi. NNE of Avalon, Catalina Island 12/17 12:52 am 34 23.3 116 27.9 2.4 18 mi. N of Yucca Valley 12/17 6:28 am 33 14.0 118 1.5 3.4 18 mi. ESE of Avalon, Catalina Island 12/17 7:39 am 34 8.9 116 50.7 2.0 3 mi. NNW of Mt. San Gorgonio 12/17 11:21 am 34 9.1 116 25.6 2.6 2 mi. NNE of Yucca Valley 12/17 11:22 am 34 8.9 116 25.8 2.7 " 12/17 1:30 pm 35 15.9 119 49.9 2.0 11 mi. ESE of Simmler 12/17 6:55 pm 34 21.8 116 27.7 2.0 16 mi. N of Yucca Valley 12/18 1:03 am 34 36.7 116 37.6 2.5 21 mi. ENE of Lucerne Valley 12/18 4:01 am 33 25.9 118 20.1 2.0 6 mi. N of Avalon, Catalina Island 12/18 4:06 am 33 24.5 118 17.4 2.0 4 mi. NNE of Avalon, Catalina Island 12/18 5:34 am 34 14.3 116 26.5 2.1 8 mi. N of Yucca Valley 12/18 7:40 am 32 20.1 115 20.7 2.8 24 mi. SSE of Calexico 12/18 7:44 am 32 21.9 115 21.8 3.2 " 12/18 7:50 am 32 17.9 115 22.0 3.0 " 12/18 7:59 am 32 19.0 115 21.0 3.1 " 12/18 8:00 am 32 22.2 115 21.0 3.3 " 12/18 8:12 am 32 20.3 115 21.1 3.1 " 12/19 1:06 am 34 15.3 116 25.9 2.5 9 mi. N of Yucca Valley 12/19 1:37 am 34 37.7 116 38.3 2.1 21 mi. NE of Lucerne Valley 12/19 3:40 am 33 22.6 116 24.7 2.2 8 mi. NNW of Borrego Springs 12/19 4:47 am 34 11.6 117 32.1 2.1 8 mi. N of the I10/I15 inter- change, Rancho Cucamonga 12/19 7:07 am 32 22.1 115 20.5 2.5 22 mi. SSE of Calexico 12/19 6:25 pm 34 1.6 116 59.9 2.5 6 mi. N of Beaumont 12/19 9:03 pm 34 22.9 116 26.8 2.8 18 mi. N of Yucca Valley 12/19 9:29 pm 34 33.2 116 31.9 2.7 24 mi. ENE of Lucerne Valley 12/19 10:07 pm 34 34.9 116 32.3 2.0 " 12/19 10:16 pm 34 34.6 116 32.6 2.8 " 12/19 10:17 pm 35 29.6 118 26.8 2.3 9 mi. S of the town of Lake Isabella 12/20 6:36 am 34 24.4 116 27.9 2.0 19 mi. N of Yucca Valley 12/20 9:37 am 32 21.9 115 21.5 4.0 24 mi. SSE of Calexico 12/20 9:46 am 32 19.3 115 21.6 2.7 " 12/20 9:59 am 32 22.4 115 21.2 2.9 " 12/20 1:23 pm 32 20.8 115 20.8 2.9 " 12/20 2:33 pm 34 18.0 116 26.1 2.4 12 mi. N of Yucca Valley 12/20 5:55 pm 34 33.5 116 31.6 2.0 25 mi. ENE 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.