SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey February 1, 1996 Weekly Earthquake Report for Southern California ------------------------------------------------ January 25 - 31, 1996 Prepared by: Kate Hutton, Seismological Laboratory (kate@bombay.gps.caltech.edu) Lucy Jones, U. S. Geological Survey California Institute of Technology 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, January 25, Universal Time (ie. GMT), to midnight Wednesday night, January 31 Universal Time. In local time, the period of coverage is from 4 p.m., January 24 to 4 p.m., January 31, Pacific Standard Time. We detected and processed 431 earthquakes during the 7-day period covered. The week's largest quake was a member of the Ridgecrest sequence: a M4.1 early Friday morning. It was felt in the Ridgecrest area. Several M3+ quakes were also felt in their respective epicentral regions. The one that attracted the most public attention was a ML3.8 Northridge of aftershock (of the January 17, 1994 Mw6.7) on Tuesday morning. It was located in the mountains about a mile north of the 210 freeway and a couple of miles east of the 14 freeway, and was felt as far away as Pasadena. Our station at Sylmar (SYL) recorded a peak acceleration of 3.37% g. This means that the ground moved with an acceleration of 3.37% of that of gravity, which is about the most one would expect near the epicenter of a M3.8. Statistically speaking, we can expect one or two more M4+ aftershocks in the Northridge sequence in the next year, the third year of the sequence. Also in the next year, there should be about 12 M3's, and perhaps 100 M2's, and so forth. By the tenth year of the sequence, the aftershock rate will have decayed to the point where we expect a M3 only once a year. At that point, practically speaking, one might say the sequence is over, although a "blob" of very small quakes will still be visible on the map. That will be in 2004. Last Wednesday night, a M3.5 Landers aftershock (of the June 28, 1992 Mw7.3) was felt in the Yucca Valley area. On Saturday afternoon, a M2.7 was felt by a few people in the Loma Linda area. There were two more M3+ quakes that apparently escaped public attention: a M3.1 on Saturday evening in the desert east of Goldstone Lake, and a M3.2 Ridgecrest quake late Tuesday afternoon. 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 Pacific Daylight Time or 8 hrs to the Pacific Standard Time listed. Table 1 ------- Date Time N Lat. W Long. Mag ------------------------------------------------------------- 1/24 6:59 pm 34 8.8 116 25.8 2.2 2 mi. NNE of Yucca Valley 1/24 9:35 pm 34 9.8 116 26.8 3.5 3 mi. N of Yucca Valley FELT in Yucca Valley 1/24 11:11 pm 35 44.8 117 38.1 2.1 8 mi. NNE of Ridgecrest 1/25 2:58 am 34 16.1 118 27.2 2.8 1 mi. SW of Pacoima 1/25 3:00 am 34 20.5 118 32.3 2.2 2 mi. SSW of Newhall 1/25 10:42 am 35 44.8 117 37.5 2.2 8 mi. NNE of Ridgecrest 1/25 5:24 pm 34 20.6 116 27.4 2.0 15 mi. N of Yucca Valley 1/25 9:24 pm 34 17.2 118 37.2 2.3 2 mi. NNW of Chatsworth 1/26 5:06 am 35 47.6 117 39.9 4.1 11 mi. N of Ridgecrest FELT in Ridgecrest 1/26 5:26 am 35 47.6 117 39.7 2.2 " 1/26 8:27 am 36 1.6 117 53.0 2.5 3 mi. ESE of Coso Junction 1/26 12:02 pm 35 43.8 117 37.5 2.2 7 mi. NNE of Ridgecrest 1/26 12:16 pm 35 47.4 117 39.5 2.1 11 mi. N of Ridgecrest 1/26 6:11 pm 35 45.3 117 38.1 2.1 9 mi. N of Ridgecrest 1/26 6:47 pm 35 47.5 117 39.9 2.8 11 mi. N of Ridgecrest 1/26 7:18 pm 32 43.4 115 54.8 2.0 4 mi. E of Ocotillo 1/26 8:45 pm 35 44.4 117 37.7 2.0 8 mi. NNE of Ridgecrest 1/27 4:45 am 35 1.9 117 0.2 2.0 10 mi. N of Barstow 1/27 8:09 am 34 11.3 116 26.2 2.5 4 mi. N of Yucca Valley 1/27 9:45 am 36 6.7 117 48.5 2.8 Coso Range, 7 mi. ESE of Haiwee Reservoir 1/27 11:17 am 36 6.2 117 49.0 2.1 " 1/27 1:52 pm 32 31.0 115 17.1 2.0 16 mi. SE of Calexico 1/27 2:42 pm 36 7.1 117 48.6 2.8 Coso Range, 7 mi. E of Haiwee Reservoir 1/27 6:47 pm 34 3.4 117 16.5 2.7 1 mi. WNW of Loma Linda FELT 1/27 8:09 pm 35 19.6 116 35.7 3.1 16 mi. E of Goldstone Lake 1/27 10:23 pm 35 44.8 117 37.6 2.5 8 mi. NNE of Ridgecrest 1/27 10:46 pm 33 46.4 116 6.8 2.0 7 mi. NE of Indio 1/27 11:22 pm 33 58.4 116 46.9 2.1 3 mi. N of Cabazon 1/28 11:39 am 35 42.0 117 42.6 2.8 5 mi. NNW of Ridgecrest 1/28 11:40 pm 33 22.2 116 19.4 2.2 8 mi. NNE of Borrego Springs 1/29 3:21 am 35 20.0 118 31.2 2.0 14 mi. NNW of Tehachapi 1/29 10:27 am 34 35.3 116 32.5 2.0 25 mi. ENE of Lucerne Valley 1/29 1:52 pm 34 8.6 116 25.1 2.0 2 mi. NE of Yucca Valley 1/29 2:06 pm 36 0.5 117 48.6 2.1 Coso Range, 8 mi. ESE of Coso Junction 1/29 2:26 pm 36 1.8 117 53.4 2.3 Coso Range, 3 mi. ESE of Coso Junction 1/29 6:35 pm 33 24.8 119 6.0 2.3 4 mi. SSW of Santa Barbara Is. 1/29 9:22 pm 36 19.6 120 16.8 2.5 13 mi. NNE of Coalinga 1/30 1:36 am 36 37.5 117 43.7 2.2 18 mi. E of Lone Pine 1/30 7:30 am 35 47.5 117 39.6 2.7 11 mi. N of Ridgecrest 1/30 10:34 am 34 20.2 118 28.6 3.8 4 mi. SE of Newhall Widely FELT 1/30 11:12 am 34 29.3 116 30.6 2.1 25 mi. N of Yucca Valley 1/30 11:14 am 36 1.7 117 53.0 2.5 3 mi. ESE of Coso Junction 1/30 3:35 pm 33 31.0 116 30.9 2.1 9 mi. ESE of Anza 1/30 5:35 pm 35 46.3 117 37.2 3.2 10 mi. NNE of Ridgecrest 1/30 11:36 pm 34 17.6 118 29.7 2.2 1 mi. NNE of Granada Hills 1/31 2:30 am 34 22.8 118 40.3 2.5 7 mi. NNE of Simi Valley 1/31 3:11 pm 34 38.0 116 30.0 2.1 28 mi. ENE of Lucerne Valley -------------------------------------------------------------