SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey June 15, 1995 Weekly Earthquake Report for Southern California ------------------------------------------------ June 8 - 14, 1995 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, June 8, Pacific Daylight Time, to midnight Wednesday night, June 14, 1995, Pacific Daylight Time. We recorded 312 earthquakes of M1.0 or larger during the 7-day period covered. We had a fairly active week, with almost 50% more quakes than we have been seeing recently. The increase occurred at several different locations around the region. One area of interest was the Obsidian Butte area in the Imperial Valley, along the southeastern coast of the Salton Sea. Obsidian Butte has produced numerous swarms in the past, and this week's was fairly minor by comparison. There were, however, 19 events above M1, the largest of which was a M2.8 early Monday afternoon. As far as we know, it was not felt. Another area that showed itself was the section of the Landers aftershock zone northeast of Barstow. The largest of these, M3.5 last Thursday afternoon, was felt. It's mechanism was mostly strike-slip, consistent with what we've seen so far from the Landers sequence. There were 33 events total in this area, and three of them (including the M3.5) had magnitudes of M3 or above. The largest quake of the week occurred 15 minutes after the Obsidian Butte M2.8 early Monday afternoon, along the eastern front of the Sierra Nevada, northwest of Olancha. It had a magnitude of M3.6, but we did not get any inquiries about it. The second largest quake of the week was a M3.4 near Lake Henshaw, in the Elsinore Fault zone. It occurred early Friday afternoon and was felt. The focal mechanism shows a combination of strike-slip and normal (tensional) faulting. Another minor swarm occurred in the Wheeler Ridge area, near Grapevine. Although there were 24 members above M1, none were larger than M2.0. The Northridge sequence did not seem to show any particular increase. The largest event there was a M2.9 on Monday evening in the Northridge area, that was felt. Not surprisingly, it had a thrust mechanism. 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 ------------------------------------------------------------- 6/8 7:35 am 34 16.2 118 32.0 2.0 2 mi. N of Northridge 6/8 2:09 pm 32 36.8 115 20.0 2.0 10 mi. ESE of Calexico 6/8 3:12 pm 36 3.9 117 42.3 2.2 13 mi. E of Coso Junction 6/8 3:32 pm 34 59.3 116 56.5 3.5 8 mi. NNE of Barstow FELT 6/8 10:02 pm 34 37.3 116 34.1 2.0 24 mi. ENE of Lucerne Valley 6/8 10:51 pm 36 2.4 120 34.7 2.5 12 mi. NW of Parkfield 6/9 1:45 am 34 55.8 116 55.2 3.1 6 mi. ENE of Barstow 6/9 3:25 am 34 56.0 116 55.2 2.7 " 6/9 9:07 am 33 11.6 115 34.9 2.1 Obsidia Butte area, 4 mi. SW of Niland 6/9 9:30 am 35 2.5 116 58.7 2.6 10 mi. NNE of Barstow 6/9 12:44 pm 33 16.4 116 48.7 3.4 3 mi. NW of Lake Henshaw FELT 6/9 4:11 pm 34 23.4 116 28.1 2.0 18 mi. N of Yucca Valley 6/9 6:05 pm 34 2.2 117 14.7 2.0 1 mi. SE of Loma Linda 6/9 8:50 pm 33 21.7 116 21.3 2.0 7 mi. N of Borrego Springs 6/10 2:51 am 34 14.6 118 27.5 2.0 2 mi. SSW of San Fernando 6/10 4:37 am 33 42.2 116 49.3 2.7 6 mi. WSW of Idyllwild 6/10 11:28 am 34 16.2 118 29.0 2.0 2 mi. WSW of San Fernando 6/10 5:38 pm 33 10.9 115 36.3 2.2 Obsidian Butte area, 6 mi. SW of Niland 6/10 9:42 pm 34 56.4 116 53.2 2.9 8 mi. ENE of Barstow 6/10 10:20 pm 34 56.4 116 53.1 3.0 " 6/10 10:31 pm 34 21.5 116 27.3 2.0 16 mi. N of Yucca Valley 6/10 10:48 pm 34 56.3 116 53.3 2.0 8 mi. ENE of Barstow 6/11 1:14 am 34 38.0 120 48.2 2.2 9 mi. WNW of Pt. Arguello 6/11 4:48 am 34 56.3 116 53.2 2.0 8 mi. ENE of Barstow 6/11 8:38 am 34 39.4 120 50.0 2.1 11 mi. WNW of Pt. Arguello 6/11 4:05 pm 34 27.3 117 47.8 2.1 11 mi. NW of Wrightwood 6/12 7:59 am 33 31.8 117 59.8 2.2 7 mi. SSW of Newport Beach 6/12 8:08 am 34 3.4 117 15.6 2.0 1 mi. N of Loma Linda 6/12 10:19 am 32 38.9 115 49.5 2.1 11 mi. ESE of Ocotillo 6/12 12:16 pm 34 56.3 116 53.8 2.1 7 mi. ENE of Barstow 6/12 12:34 pm 33 54.1 119 19.5 2.3 14 mi. SE of Santa Cruz Is. 6/12 2:08 pm 33 10.8 115 36.1 2.8 Obsidian Butte area, 6 mi. SW of Niland; FELT 6/12 2:23 pm 36 20.4 118 4.9 3.6 5 mi. NW of Olancha 6/12 2:35 pm 36 19.5 118 5.1 2.4 " 6/12 2:48 pm 34 10.7 116 48.9 2.5 5 mi. N of Mt. San Gorgonio 6/12 5:34 pm 35 3.0 119 2.7 2.0 Wheeler Ridge, 5 mi. WNW of the I5/99 interchange 6/12 9:53 pm 34 15.9 118 30.5 2.9 2 mi. NE of Northridge FELT 6/13 10:02 am 34 3.3 117 15.8 2.1 1 mi. N of Loma Linda 6/13 12:53 pm 34 13.7 116 44.6 2.4 6 mi. ESE of Big Bear City 6/13 7:35 pm 34 13.2 118 35.6 2.2 1 mi. NNE of Canoga Park 6/13 8:33 pm 33 42.7 116 50.4 2.1 7 mi. WSW of Idyllwild 6/13 10:02 pm 34 7.2 116 52.0 2.3 2 mi. WNW of Mt. San Gorgonio 6/14 12:48 am 34 21.2 116 27.8 2.5 16 mi. N of Yucca Valley 6/14 5:06 am 34 37.4 116 35.8 2.7 23 mi. ENE of Lucerne Valley 6/14 9:05 am 33 47.9 117 7.9 2.1 9 mi. WNW of Hemet 6/14 11:37 am 33 9.8 116 4.9 2.1 3 mi. ENE of Ocotillo Wells 6/14 12:41 pm 33 52.4 116 51.5 2.0 3 mi. SSE of Banning 6/14 6:09 pm 35 4.0 119 2.5 2.0 Wheeler Ridge, 5 mi. WNW of the I5/99 interchange -------------------------------------------------------------