May 26, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ May 19 - 25, 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, May 19, Pacific Daylight Time, to midnight Wednesday night, May 25, Pacific Daylight Time. We recorded 401 earthquakes this week. All of the earthquakes felt this week were Northridge aftershocks. The largest was, of course, the M4.2 at 5:56 am on yesterday, Wednesday. It woke many people up as far away as Ventura and Pasadena. The focal mechanism was thrust, on a nearly east-west striking fault plane, as most Northridge aftershocks have been. M4.2 is slightly smaller than the M4.5 we gave it at the time; this is because we've had the time to consider more data. As our readers know well, it is common for us to revise magnitudes in the first few days after a quake. This quake had a few aftershocks of its own, but all were too small to feel. Later on Wednesday, at 2:41 pm, a M3.0 occurred about four miles away, and was also felt. Earlier, a M2.8 in the Canoga Park area, on Sunday morning, was felt. On Tuesday afternoon, a M3.1 in the San Fernando area was also felt. This all goes to show that the Northridge aftershock sequence is behaving quite normally. At this point, four months after the mainshock, we should be having two to three M3.0 or larger events per week, and one M4.0 or larger about once a month. The last aftershock above M4.0 was the M5.3 on Sunday, March 20, somewhat more than two months ago. 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 ------------------------------------------------------------- 5/19 12:09 am 33 31.5 114 33.1 2.6 6 mi. SSE of Blythe 5/19 1:13 am 34 19.8 118 25.7 2.0 3 mi. N of San Fernando 5/19 2:20 am 34 19.7 118 26.1 2.1 " 5/19 6:29 am 34 4.2 116 21.9 2.2 5 mi. SE of Yucca Valley 5/19 7:28 am 36 0.8 117 25.5 2.0 17 mi. N of Trona 5/19 7:44 am 34 13.7 117 28.5 2.2 Lytle Creek, 3 mi. W of the I15/I215 interchange 5/19 10:22 am 34 21.1 118 29.2 2.1 2 mi. SE of Newhall 5/19 1:52 pm 32 49.1 116 5.3 2.0 7 mi. NW of Ocotillo 5/19 7:26 pm 34 19.1 118 28.3 2.0 3 mi. NW of San Fernando 5/19 8:37 pm 32 46.7 115 26.4 2.0 6 mi. E of El Centro 5/20 1:24 am 34 18.1 118 28.0 2.0 2 mi. NW of San Fernando 5/20 2:22 am 35 23.9 117 49.8 2.5 18 mi. SSW of Ridgecrest 5/20 3:09 am 33 0.5 117 46.4 2.6 26 mi. WSW of Oceanside 5/20 11:37 am 34 22.5 116 27.9 2.1 17 mi. N of Yucca Valley 5/20 12:38 pm 34 23.5 116 27.9 2.1 " 5/20 1:19 pm 34 56.5 116 46.4 2.3 14 mi. ENE of Barstow 5/20 3:24 pm 34 9.2 116 24.8 2.0 3 mi. NE of Yucca Valley 5/20 11:48 pm 34 13.6 118 33.8 2.7 1 mi. WSW of Northridge 5/21 1:33 am 32 53.1 116 15.5 2.0 19 mi. SSW of Ocotillo Wells 5/21 8:56 am 34 31.4 116 33.3 2.0 24 mi. NE of Big Bear City 5/21 3:31 pm 33 57.8 116 18.7 2.2 10 mi. E of Desert Hot Springs 5/21 3:31 pm 34 28.0 118 37.9 2.4 3 mi. SSW of Castaic Lake dam 5/21 3:32 pm 34 28.1 118 37.8 2.0 " 5/21 3:34 pm 33 57.7 116 18.9 2.1 10 mi. E of Desert Hot Springs 5/21 5:39 pm 34 18.6 116 26.2 2.0 13 mi. N of Yucca Valley 5/21 6:46 pm 34 14.8 118 29.2 2.6 2 mi. ENE of Northridge 5/21 9:47 pm 34 17.8 118 29.3 2.4 3 mi. WNW of San Fernando 5/22 12:05 am 34 22.4 118 35.1 2.2 3 mi. S of Magic Mtn. 5/22 7:27 am 34 15.6 118 36.5 2.4 4 mi. N of Canoga Park 5/22 8:34 am 34 16.0 118 36.4 2.8 " FELT 5/22 9:14 am 35 54.9 117 18.9 2.0 10 mi. NNE of Trona 5/22 9:44 am 34 5.2 116 22.8 2.0 4 mi. ESE of Yucca Valley 5/22 2:55 pm 34 19.0 119 45.4 2.2 7 mi. SSW of Santa Barbara 5/22 4:14 pm 34 23.1 118 38.8 2.6 4 mi. SW of Magic Mtn. 5/22 6:36 pm 34 23.4 118 38.8 2.2 " 5/22 6:54 pm 34 16.1 118 35.5 2.2 4 mi. WNW of Northridge 5/22 9:28 pm 34 29.1 116 30.8 2.4 25 mi. N of Yucca Valley 5/23 1:33 am 35 1.6 116 58.5 2.3 9 mi. NNE of Barstow 5/23 1:54 am 34 22.1 118 44.4 2.4 6 mi. NNW of Simi Valley 5/23 2:14 am 34 14.9 118 33.3 2.5 1 mi. NW of Northridge 5/23 3:18 am 34 21.7 118 44.3 2.1 6 mi. NNW of Simi Valley 5/23 7:11 am 34 19.2 118 28.3 2.5 3 mi. NW of San Fernando 5/23 8:26 am 34 22.0 118 44.8 2.5 6 mi. NNW of Simi Valley 5/23 9:24 am 33 10.3 115 35.2 2.0 5 mi. NW of Calipatria 5/23 2:53 pm 34 17.8 118 28.4 2.0 2 mi. WNW of San Fernando 5/23 7:36 pm 34 57.5 116 45.8 2.1 15 mi. ENE of Barstow 5/23 11:20 pm 34 19.6 118 25.7 2.0 3 mi. N of San Fernando 5/24 5:59 am 34 11.2 116 25.9 2.0 4 mi. N of Yucca Valley 5/24 8:41 am 34 37.4 116 33.2 2.9 25 mi. ENE of Lucerne Valley 5/24 1:56 pm 34 15.7 118 28.1 3.1 2 mi. SW of San Fernando FELT 5/24 2:14 pm 33 57.9 116 19.5 2.0 10 mi. E of Desert Hot Springs 5/24 11:31 pm 34 16.7 118 35.9 2.7 4 mi. NW of Northridge 5/25 4:01 am 34 19.6 118 36.0 2.1 5 mi. SW of Newhall 5/25 5:52 am 34 33.2 116 32.3 2.1 24 mi. ENE of Lucerne Valley 5/25 5:56 am 34 18.7 118 23.6 4.2 3 mi. NE of San Fernando FELT 5/25 6:02 am 34 18.5 118 23.1 2.0 " 5/25 6:02 am 34 19.2 118 23.4 2.1 " 5/25 6:03 am 34 18.5 118 23.4 2.2 " 5/25 6:05 am 34 18.6 118 23.4 2.1 " 5/25 6:06 am 34 18.6 118 24.3 2.0 " 5/25 6:25 am 34 19.1 118 23.3 2.1 " 5/25 6:27 am 34 19.1 118 23.2 2.2 " 5/25 6:32 am 34 59.5 116 56.8 2.7 8 mi. NNE of Barstow 5/25 6:32 am 34 18.8 118 23.9 2.5 3 mi. NE of San Fernando 5/25 7:06 am 35 20.9 117 54.3 2.1 23 mi. SW of Ridgecrest 5/25 7:13 am 34 37.6 116 35.0 2.2 24 mi. ENE of Lucerne Valley 5/25 7:23 am 34 19.0 118 23.3 2.1 3 mi. NE of San Fernando 5/25 10:03 am 33 54.1 116 17.4 2.1 13 mi. NNW of Indio 5/25 11:01 am 34 18.6 118 26.3 2.2 1 mi. N of San Fernando 5/25 11:05 am 34 19.3 118 23.0 2.5 4 mi. NE of San Fernando 5/25 11:54 am 36 2.5 117 48.3 2.3 7 mi. E of Coso Junction 5/25 11:56 am 34 23.1 116 27.3 2.4 18 mi. N of Yucca Valley 5/25 2:25 pm 35 55.5 117 37.5 2.0 17 mi. NW of Trona 5/25 2:41 pm 34 16.2 118 27.5 3.0 1 mi. SW of San Fernando FELT 5/25 8:29 pm 34 37.3 116 29.9 2.2 28 mi. ENE of Lucerne 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.