October 6, 1994 Weekly Earthquake Report for Southern California ------------------------------------------------ September 29 - October 5, 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, September 29, Pacific Daylight Time, to midnight Wednesday night, October 5, Pacific Daylight Time. We recorded only 255 earthquakes of M1.0 or larger this week. The most widely felt event this week occurred just south of the area shown on the map. It was a M4.6 in northern Baja, about 55 mi. SSE of Mexicali, at 7:00 am on Tuesday morning. It was felt as far north as the Imperial Valley and Yuma, Arizona. This area is the transition between the East Pacific Rise spreading ridge and the southern end of the San Andreas Fault at the Salton Sea, and is very active seismically. The largest event inside our coverage area was a M3.1 in the Solvang area, early Monday morning. Although it was certainly large enough to feel, no-one called us about it. The only quake that was reported felt was a M2.7 Northridge aftershock on Friday morning. Notice the low number of events this week. Although, statistically, the number of quakes varies from week to week, a slow overall decline is apparent with the decline of the two major aftershock sequences (Landers/Big Bear and Northridge). For statistics buffs, we present a summary of the events processed so far from these sequences (through September 30): Northridge ---------- All events 10,314+ 3.0 - 3.9 409 4.0 - 4.9 49 5.0 and up 9 GMT date GMT time Latitude Longitude Depth Mag 1994 1 17 12 30 55.39 34 12.80 -118 32.22 18.40 6.7 1994 1 17 12 31 57.82 34 16.76 -118 28.43 0.00 5.9 1994 1 17 12 40 35.71 34 20.49 -118 36.10 0.01 5.2 1994 1 17 23 33 30.69 34 19.58 -118 41.90 9.83 5.6 1994 1 18 0 43 8.89 34 22.59 -118 41.89 11.34 5.2 1994 1 19 21 9 28.61 34 22.71 -118 42.64 14.44 5.1 1994 1 19 21 11 44.90 34 22.65 -118 37.06 11.33 5.1 1994 1 29 11 20 35.95 34 18.32 -118 34.76 1.04 5.1 1994 3 20 21 20 12.26 34 13.88 -118 28.50 13.09 5.3 We are almost, but not quite, finished with the preliminary data processing of the Northridge sequence. Landers/Big Bear ---------------- All events 44,117+ 3.0 - 3.9 1,462 4.0 - 4.9 157 5.0 and up 21 GMT date GMT time Latitude Longitude Depth Mag 1992 4 23 4 50 23.22 33 57.67 -116 19.05 12.38 6.1 1992 5 18 15 44 17.97 33 57.06 -116 20.25 6.57 5.0 1992 6 28 11 57 34.13 34 12.03 -116 26.14 1.03 7.3 1992 6 28 12 0 45.00 34 7.84 -116 24.49 0.01 5.6 1992 6 28 12 1 16.19 34 7.19 -116 19.39 6.00 5.4 1992 6 28 12 36 40.64 34 8.09 -116 26.06 7.39 5.3 1992 6 28 12 40 53.82 34 19.83 -116 32.84 6.00 5.4 1992 6 28 14 43 21.85 34 9.71 -116 51.13 11.06 5.5 1992 6 28 15 5 30.73 34 12.16 -116 49.61 5.32 6.2 1992 6 28 17 1 31.92 34 10.71 -116 55.35 13.72 5.1 1992 6 28 17 5 57.56 34 15.31 -116 54.72 7.66 5.0 1992 6 29 14 8 37.73 34 6.27 -116 24.19 10.35 5.5 1992 6 29 14 13 38.78 34 6.49 -116 24.23 9.88 5.0 1992 7 1 7 40 29.90 34 19.84 -116 27.76 8.28 5.3 1992 7 5 21 18 27.14 34 34.95 -116 19.07 0.11 5.4 1992 8 17 20 41 52.12 34 11.70 -116 51.76 11.27 5.0 1992 9 15 8 47 11.29 34 3.82 -116 21.64 8.30 5.1 1992 11 27 16 0 57.49 34 20.40 -116 54.00 1.44 5.4 1992 12 4 2 8 57.50 34 22.12 -116 53.88 2.97 5.2 1993 8 21 1 46 38.40 34 1.76 -116 19.27 9.05 5.0 1994 6 16 16 24 27.52 34 16.07 -116 24.09 3.43 5.0 The total numbers of quakes in our area are: 1990 10,738 1991 9,355 1992 50,672+ 1993 20,190 1994 22,217 so far The years prior to 1990 had similar numbers to 1990, about 10,000 per year. The increase in the past 3 years has been due exclusively to the aftershocks of Landers/Big Bear and Northridge. The plus sign means that we aren't finished with that part of the Landers sequence, and there are likely to have been more quakes than the estimate given. The table lists the quakes this week 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 ------------------------------------------------------------- 9/29 12:21 am 36 46.0 118 11.6 2.3 2 mi. S of Independence 9/29 1:05 am 34 14.4 118 34.7 2.5 2 mi. W of Northridge 9/29 1:27 am 33 59.6 116 16.3 2.4 13 mi. SE of Yucca Valley 9/29 5:07 am 34 47.2 116 18.0 2.5 35 mi. SSW of Baker 9/29 9:30 am 34 47.0 116 18.1 2.0 " 9/29 12:26 pm 34 21.5 118 39.1 2.1 5 mi. SW of Magic Mtn. 9/29 2:26 pm 32 57.4 117 39.1 2.0 22 mi. SW of Oceanside 9/29 8:33 pm 34 34.5 116 37.1 2.0 20 mi. ENE of Lucerne Valley 9/29 11:44 pm 34 46.5 116 17.5 2.1 36 mi. SSW of Baker 9/30 2:24 am 34 21.4 116 28.5 2.0 16 mi. N of Yucca Valley 9/30 10:22 am 34 16.8 118 30.5 2.7 3 mi. NNE of Northridge; FELT 9/30 5:05 pm 34 48.7 120 58.3 2.2 24 mi. NW of Pt. Arguello 9/30 6:09 pm 34 46.6 117 13.6 2.1 13 mi. SW of Barstow 9/30 7:42 pm 35 3.2 116 59.3 2.6 11 mi. N of Barstow 10/1 9:41 am 34 47.4 116 18.3 2.4 35 mi. SSW of Baker 10/1 10:15 am 33 14.7 115 37.4 2.0 Obsidian Butte area, 6 mi. W of Niland 10/1 1:58 pm 34 22.1 118 36.3 2.3 3 mi. SSW of Magic Mtn. 10/1 5:02 pm 33 59.9 116 34.5 2.0 4 mi. WNW of Desert Hot Springs 10/1 6:54 pm 34 2.5 117 31.1 2.1 Fontana, 2 mi. SE of the I10/I15 interchange 10/2 3:56 am 34 9.0 116 25.4 2.1 2 mi. NNE of Yucca Valley 10/2 8:19 am 34 12.1 116 49.6 2.7 4 mi. SSE of Big Bear City 10/2 6:09 pm 35 1.4 116 58.5 2.2 9 mi. NNE of Barstow 10/2 6:19 pm 35 1.3 116 58.5 2.3 " 10/2 8:25 pm 34 21.1 118 33.5 2.3 2 mi. SW of Newhall 10/3 1:28 am 34 34.1 120 3.1 3.1 5 mi. ESE of Solvang 10/3 5:34 am 34 36.8 116 38.5 2.3 20 mi. NE of Lucerne Valley 10/3 10:14 am 33 41.8 120 6.9 2.1 17 mi. S of Santa Rosa Is. 10/3 4:50 pm 35 44.7 118 0.6 2.3 20 mi. S of Coso Junction 10/3 5:25 pm 33 11.7 115 34.1 2.8 Obsidian Butte area, 4 mi. SW of Niland 10/3 11:06 pm 34 15.7 116 35.5 2.0 12 mi. NW of Yucca Valley 10/4 3:31 am 33 47.7 117 38.7 2.0 7 mi. SW of Corona 10/4 7:22 am 34 21.0 118 33.5 2.4 2 mi. SW of Newhall 10/4 11:29 am 33 54.1 118 33.4 2.2 Offshore, 7 mi. WSW of Los Angeles Airport 10/4 1:39 pm 34 33.4 116 24.5 2.1 30 mi. N of Yucca Valley 10/4 2:37 pm 34 30.6 116 31.3 2.0 27 mi. N of Yucca Valley 10/4 3:54 pm 34 22.2 116 27.3 2.1 17 mi. N of Yucca Valley 10/4 6:45 pm 34 24.2 116 28.3 2.0 19 mi. N of Yucca Valley 10/4 7:57 pm 32 55.4 116 20.5 2.2 18 mi. SE of Julian 10/5 4:16 am 34 19.3 118 32.7 2.1 4 mi. SSW of Newhall 10/5 5:03 am 35 21.4 118 34.2 2.1 17 mi. NNW of Tehachapi 10/5 11:22 pm 36 46.0 118 12.0 2.4 2 mi. S of Independence ------------------------------------------------------------- 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.