July 7, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ June 30 - July 6, 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, June 30, Pacific Daylight Time, to midnight Wednesday night, July 6, Pacific Daylight Time. We recorded 362 earthquakes this week, which is close to the average for the past few months. This week's seismicity is very typical of what we've seen this year so far: mostly Northridge and Landers aftershocks. The largest event (M3.5) was actually in Nevada. The second largest was a M3.3 Northridge aftershock on Saturday evening. We got public inquiries about both these events. The beginning of July is a good time to summarize activity. In fact, we plan to introduce some (hopefully interesting) statistics into the Weekly Earthquake Report on a quarterly basis. Here goes: in the first quarter of 1994 there were more than 10,182 earthquakes in southern California. In the second quarter there were 6,023. Before the Landers sequence started in 1992, quarterly averages were about 2,500. The current high rates are due completely to the Northridge and Landers/Big Bear sequences. The Northridge sequence itself has chalked up the following totals since it began on January 1, 1994: All events 8,750+ 3.0 - 3.9 381 4.0 - 4.9 48 5.0 and up 8 The largest event was, of course, the M6.7 Northridge earthquake on January 17. The Landers/Big Bear has produced the following, since it started with the Joshua Tree sequence in April of 1992. All events 52,342+ 3.0 - 3.9 1,454 4.0 - 4.9 155 5.0 and up 21 The largest event was the M7.3 Landers quake on June 28, 1992, and the second largest was the M6.4 Big Bear quake the same day. 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 ------------------------------------------------------------- 6/30 9:23 am 34 18.9 118 23.5 2.4 3 mi. NE of San Fernando 6/30 2:50 pm 34 57.5 116 56.3 2.0 6 mi. NE of Barstow 6/30 7:58 pm 34 19.9 118 30.1 2.3 3 mi. SSE of Newhall 7/1 2:17 am 34 59.7 116 57.2 2.0 8 mi. NNE of Barstow 7/1 10:57 am 36 44.3 116 16.4 3.5 37 mi. ENE of Furnace Creek, Death Valley; FELT 7/1 2:32 pm 33 16.8 118 19.1 2.6 4 mi. S of Avalon, Catalina Island 7/1 5:10 pm 35 1.5 116 59.6 2.1 9 mi. N of Barstow 7/1 6:46 pm 34 20.3 116 28.0 2.6 15 mi. N of Yucca Valley 7/1 7:27 pm 34 11.6 118 39.2 2.1 2 mi. W of Canoga Park 7/2 12:45 am 34 55.9 116 55.7 2.0 6 mi. ENE of Barstow 7/2 2:51 am 34 9.3 116 25.8 2.1 2 mi. NNE of Yucca Valley 7/2 3:53 am 32 35.8 117 5.2 2.1 4 mi. NW of San Ysidro 7/2 11:18 am 34 20.7 116 27.8 2.1 15 mi. N of Yucca Valley 7/2 11:53 am 33 41.7 118 2.5 2.0 4 mi. SE of Seal Beach 7/2 2:39 pm 34 37.5 116 38.2 2.4 21 mi. NE of Lucerne Valley 7/2 4:25 pm 34 20.4 116 28.1 2.2 15 mi. N of Yucca Valley 7/2 5:54 pm 34 14.5 118 28.2 2.8 3 mi. SSW of San Fernando 7/2 6:25 pm 34 16.6 116 24.8 2.1 11 mi. N of Yucca Valley 7/2 7:13 pm 34 17.4 118 27.4 3.3 1 mi. WNW of San Fernando FELT 7/2 7:13 pm 34 19.0 118 28.5 2.8 3 mi. NW of San Fernando 7/2 10:05 pm 34 20.2 116 28.0 2.9 15 mi. N of Yucca Valley 7/3 12:16 am 34 19.8 116 52.6 2.3 4 mi. NNW of Big Bear City 7/3 12:31 am 36 1.0 119 51.0 2.8 29 mi. ESE of Coalinga 7/3 12:53 am 34 54.8 116 55.0 2.3 6 mi. ENE of Barstow 7/3 1:23 pm 34 18.4 116 26.6 2.3 12 mi. N of Yucca Valley 7/3 2:51 pm 34 47.1 116 17.6 2.5 35 mi. SSW of Baker 7/3 4:11 pm 34 15.3 116 47.2 2.0 3 mi. E of Big Bear City 7/3 6:19 pm 36 4.6 117 52.3 2.7 4 mi. ENE of Coso Junction 7/3 9:45 pm 33 42.0 119 41.4 2.1 24 mi. SSW of Santa Cruz Is. 7/3 11:37 pm 35 54.9 117 25.7 2.3 10 mi. NNW of Trona 7/4 5:43 am 34 43.1 120 37.5 2.0 9 mi. N of Pt. Arguello 7/4 7:53 am 34 18.8 118 23.2 2.1 3 mi. NE of San Fernando 7/4 7:54 am 34 18.8 118 23.2 2.1 " 7/4 10:27 am 34 3.0 116 19.5 2.3 8 mi. SE of Yucca Valley 7/4 10:30 am 33 40.4 117 59.1 2.0 5 mi. NW of Newport Beach 7/4 12:36 pm 34 15.9 118 57.4 2.0 5 mi. NE of Camarillo 7/4 5:38 pm 34 27.8 116 29.7 2.0 24 mi. N of Yucca Valley 7/4 7:30 pm 34 16.9 118 27.8 2.0 1 mi. W of San Fernando 7/4 7:37 pm 34 14.7 118 33.5 2.3 1 mi. WNW of Northridge 7/4 8:09 pm 34 47.3 116 17.8 2.1 35 mi. SSW of Baker 7/5 1:08 am 34 18.5 118 31.9 2.1 4 mi. N of Northridge 7/5 3:31 am 34 16.9 118 27.6 2.1 1 mi. W of San Fernando 7/5 3:42 am 34 16.8 118 27.8 2.3 " 7/5 3:44 am 34 17.5 118 27.9 2.1 " 7/5 5:44 am 34 17.7 116 56.6 2.5 4 mi. NNW of town of Big Bear Lake 7/5 10:30 am 34 15.5 118 28.9 2.2 2 mi. WSW of San Fernando 7/5 2:02 pm 34 0.0 118 1.9 2.0 Rose Hills Memorial Park, 4 mi. SSW of the I10/I605 interchange 7/5 4:10 pm 34 23.1 116 27.3 2.1 18 mi. N of Yucca Valley 7/5 7:53 pm 34 9.3 116 26.2 2.1 2 mi. N of Yucca Valley 7/5 8:35 pm 33 48.8 117 38.1 2.0 5 mi. SW of Corona 7/6 12:41 am 34 15.9 118 27.6 2.3 1 mi. SW of San Fernando 7/6 12:41 am 34 11.7 117 24.3 2.0 Under Glen Helen Regional Park, Cajon Pass 7/6 1:24 am 34 23.4 116 27.7 2.2 18 mi. N of Yucca Valley 7/6 6:15 am 34 25.0 116 30.3 2.2 20 mi. N of Yucca Valley 7/6 9:08 am 33 59.7 117 4.1 2.2 7 mi. NW of Beaumont 7/6 5:57 pm 34 14.9 116 25.8 2.3 8 mi. N of Yucca Valley 7/6 6:58 pm 34 47.0 116 17.7 2.2 35 mi. SSW of Baker 7/6 7:19 pm 34 15.1 118 39.6 2.2 3 mi. ESE of Simi Valley ------------------------------------------------------------- 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.