SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey January 29, 1998 Weekly Earthquake Report for Southern California ------------------------------------------------ January 22 - 28, 1998 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 626-395-6327. For daily updates, call our Earthquake Information Hotline: 626-395-6977. -------------------------------- ****************************************************************** As many of you know by now, the U.S. Geological Survey in Menlo Park, the office which originates the Northern California Earthquake Report, is planning to discontinue the paper (and faxed) Report at the end of February 1998. We plan to follow their initiative. As of the beginning of March 1998, we will be replacing our weekly 'treeware' product with a Web site, which will include the same map, table, and commentary as the current Weekly Report, plus other features. The Web page will be updated more often than once per week. You will be able to get to this web site form the following home pages: http://www.gps.caltech.edu/seismo/ http://www-socal.wr.usgs.gov/ http://www.scecdc.scec.org/ http://www.trinet.org/ (The last one does not exist yet, but will soon.) There will be no paper copy or usenet distribution. We hope we are giving our Users sufficient notice to obtain World Wide Web access for themselves. At minimum, most public libraries now provide Web access, along with the capability to print copies of Web pages. ****************************************************************** This week's Report covers the time period from midnight Wednesday morning, January 22, Universal Time (ie. UTC), to midnight Wednesday night, January 28, Universal Time. In local time, the period of coverage is from 4 p.m., January 21, Pacific Standard Time, to 4 p.m., January 28, Pacific Standard Time. We detected 207 earthquakes during the seven-day period covered. Note that we have decided to extend the production of the Weekly Report through February, or until we have thoroughly tested some of our newest software. There were actually several M3+ quakes this week. The first one occurred last Thursday night along the Elsinore Fault near Julian. It had a magnitude of M3.1 and a strike-slip focal mechanism, and was felt in the epicentral area. There were two M3+ Landers aftershocks: a M3.2 on Monday afternoon north of Lucerne Valley, and a M3.0 near Barstow on Monday evening. Both mechanisms are consistent with the known strike-slip motion of the Landers earthquake sequence. In between these two Landers quakes, time wise, there was a M3.5 (the week's largest) along the U.S./Mexico border near the town of Ocotillo. This is a fairly common source of small quakes, but is not part of an aftershock sequence. In addition to all these M3's, there was a pair of M2.9's in Orange County early Friday morning, which were reported felt. Curiously, the two had different focal mechanisms, the first one being pure thrust and the second one having oblique slip. Table 1 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 ------------------------------------------------------------- 1/22 12:02 am 34 22.8 118 36.9 2.0 3 mi. WSW of Valencia 1/22 10:37 pm 33 14.5 118 42.6 2.1 15 mi. NNW of San Clemente Is. (NW tip) 1/22 11:50 pm 32 58.5 116 27.0 3.1 11 mi. SE of Julian FELT 1/23 4:49 am 33 48.1 117 48.6 2.9 2 mi. ENE of Orange FELT in Orange County 1/23 5:04 am 33 48.2 117 48.6 2.9 " also FELT 1/23 10:14 am 33 10.7 115 33.6 2.0 4 mi. NW of Calipatria 1/23 10:38 am 36 20.3 117 57.2 2.0 4 mi. NE of Olancha 1/23 4:16 pm 33 47.2 117 49.6 2.2 1 mi. E of Orange 1/24 12:25 am 32 47.9 115 27.6 2.3 5 mi. E of El Centro 1/24 1:01 am 36 20.3 117 57.4 2.7 4 mi. NE of Olancha 1/24 2:11 am 32 58.4 116 26.9 2.0 11 mi. SE of Julian 1/24 10:05 am 32 40.2 115 56.0 2.1 5 mi. SE of Ocotillo 1/24 3:53 pm 32 36.3 116 6.8 2.1 11 mi. SW of Ocotillo 1/24 4:23 pm 34 7.3 116 56.5 2.0 6 mi. WNW of Mt. San Gorgonio 1/24 6:46 pm 36 26.0 117 53.1 2.3 12 mi. NNE of Olancha 1/26 9:24 am 34 58.4 116 48.6 2.1 13 mi. ENE of Barstow 1/26 11:27 am 34 58.8 116 56.8 2.8 7 mi. NE of Barstow 1/26 3:27 pm 34 37.4 116 40.3 3.2 19 mi. NE of Lucerne Valley 1/26 4:03 pm 32 39.0 116 13.6 3.5 14 mi. WSW of Ocotillo 1/26 8:11 pm 34 58.9 116 56.8 3.0 7 mi. NE of Barstow 1/26 8:13 pm 34 58.8 116 56.8 2.6 " 1/26 8:16 pm 34 58.8 116 56.8 2.3 " 1/26 10:59 pm 34 58.8 116 56.9 2.2 " 1/27 3:03 am 36 11.4 118 18.6 2.0 18 mi. WSW of Olancha 1/27 6:56 am 35 31.3 118 25.5 2.3 8 mi. SSE of town of Lake Isabella 1/27 7:29 am 33 46.7 116 11.3 2.2 4 mi. NNE of Indio 1/27 1:37 pm 33 17.1 117 50.5 2.0 14 mi. SSW of Dana Point 1/27 5:23 pm 35 5.1 117 30.4 2.3 10 mi. NE of Boron 1/27 7:46 pm 36 4.9 117 38.1 2.2 17 mi. E of Coso Junction 1/28 12:07 am 35 1.4 118 25.2 2.2 7 mi. S of Tehachapi 1/28 12:56 pm 34 0.6 117 33.2 2.6 7 mi. SSE of Rancho Cucamonga -------------------------------------------------------------