SOUTHERN CALIFORNIA SEISMOGRAPHIC NETWORK A Cooperative Project of Caltech and the U.S. Geological Survey June 26, 1997 Weekly Earthquake Report for Southern California ------------------------------------------------ June 19 - 25, 1997 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 818-395-6327. For daily updates, call our Earthquake Information Hotline: 818-395-6977. -------------------------------- This week's Report covers the time period from midnight Thursday morning, June 19, Universal Time (ie. GMT), to midnight Wednesday night, June 25, Universal Time. In local time, the period of coverage is from 5 p.m., June 18, Pacific Daylight Time, to 5 p.m., June 25, Pacific Daylight Time. We detected 249 earthquakes during the seven-day period covered. These Weekly Reports should not be used for archival purposes. Further data processing often changes the magnitudes slightly and, especially during times of high seismicity, sometimes changes the estimates of total seismicity. For the best earthquake catalog currently available, see: http://scec.gps.caltech.edu/catalog-search.html The most excitement this week occurred southeast of San Clemente Island. Last Thursday evening and Friday morning, there were three quakes out there that measured M4 or larger: a M4.7, a M4.2, and a M4.6. The largest two were felt in the Orange County area and in San Diego. There were also two after- shocks in this sequence that were in the M3+ range, and many M2's. Because our station density is low in the offshore region, basically limited to the major islands, we cannot make as precise statements about these quakes as we can for onshore events. It appears, however, that the focal mechanisms were oblique strike-slip, with a strike consistent with the San Clemente Fault, which is the major fault you see on the map going through that area. The epicenters are probably more tightly clustered that they appear to be, since, in that area, the uncertainty in our locations is significant. The only other earthquakes above M3 were: a M3.5 very early Monday morning in Imperial Valley, and a M3.4 in the Tehachapi area on Monday evening. The Imperial Valley quake had a strike-slip mechanism, as one would expect along the nearby Imperial Fault. The Tehachapi quake also appears to have been mostly strike slip. It occurred near the famous White Wolf Fault, which was responsible for the 1952 Kern County earthquake (Mw7.5), the largest earthquake in the region so far this century. 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 ------------------------------------------------------------- 6/18 7:34 pm 34 22.3 116 28.2 2.3 17 mi. N of Yucca Valley 6/18 9:47 pm 32 37.1 115 53.9 2.0 9 mi. SE of Ocotillo 6/19 12:45 am 35 47.0 117 39.5 2.3 11 mi. N of Ridgecrest 6/19 6:31 pm 32 49.0 115 36.6 2.3 3 mi. WNW of El Centro 6/19 9:35 pm 32 40.8 118 6.5 4.7 16 mi. SE of San Clemente Is. (SE tip) WIDELY FELT 6/19 9:53 pm 32 38.3 118 9.9 2.6 " 6/19 10:13 pm 34 27.8 119 18.5 2.0 3 mi. WNW of Ojai 6/19 10:38 pm 32 41.1 118 8.2 4.2 15 mi. SE of San Clemente Is. (SE tip) 6/20 1:04 am 32 37.5 118 9.0 4.6 17 mi. SE of San Clemente Is. (SE tip) FELT 6/20 2:17 am 32 46.6 118 6.8 2.6 13 mi. ESE of San Clemente Is. (SE tip) 6/20 3:51 am 32 38.7 118 8.5 2.9 16 mi. SE of San Clemente Is. (SE tip) 6/20 4:17 am 32 43.3 118 7.9 3.5 14 mi. ESE of San Clemente Is. (SE tip) 6/20 5:42 am 32 37.4 118 10.0 3.0 17 mi. SE of San Clemente Is. (SE tip) 6/20 12:12 pm 32 44.4 118 5.8 2.3 15 mi. ESE of San Clemente Is. (SE tip) 6/20 3:56 pm 32 26.9 115 27.8 2.9 15 mi. S of Calexico 6/20 4:26 pm 32 40.6 117 8.0 2.3 3 mi. SSE of San Diego 6/20 6:03 pm 32 42.8 118 9.6 2.5 13 mi. SE of San Clemente Is. (SE tip) 6/20 7:38 pm 32 45.7 118 8.5 2.2 12 mi. ESE of San Clemente Is. (SE tip) 6/20 9:57 pm 32 44.4 118 7.8 2.0 13 mi. ESE of San Clemente Is. (SE tip) 6/21 1:59 am 34 21.7 116 28.1 2.1 16 mi. N of Yucca Valley 6/21 8:21 am 33 37.8 116 42.3 2.0 5 mi. NNW of Anza 6/21 9:05 am 32 9.3 115 48.0 2.7 39 mi. SSW of Calexico 6/21 1:29 pm 32 39.2 118 8.9 2.2 16 mi. SE of San Clemente Is. (SE tip) 6/21 1:33 pm 35 58.8 117 40.7 2.3 15 mi. ESE of Coso Junction 6/21 3:18 pm 34 58.5 116 48.5 2.0 13 mi. ENE of Barstow 6/22 7:08 am 32 43.4 118 8.8 2.9 13 mi. ESE of San Clemente Is. (SE tip) 6/22 8:58 am 35 58.9 117 40.6 2.0 15 mi. ESE of Coso Junction 6/22 9:54 am 32 42.3 118 7.9 2.3 14 mi. ESE of San Clemente Is. (SE tip) 6/22 1:17 pm 33 57.5 119 54.4 2.0 7 mi. S of Santa Cruz Is. 6/22 1:24 pm 32 41.2 118 7.3 2.0 15 mi. SE of San Clemente Is. (SE tip) 6/22 1:57 pm 33 57.8 116 56.6 2.1 3 mi. NE of Beaumont 6/22 5:57 pm 34 23.0 119 31.8 2.1 1 mi. SW of Carpinteria 6/23 12:40 am 34 22.8 118 38.6 2.1 4 mi. WSW of Valencia 6/23 12:57 am 32 44.0 115 25.9 3.5 5 mi. NE of Calexico 6/23 2:27 am 32 45.3 115 26.0 2.1 6 mi. NNE of Calexico 6/23 6:12 am 33 10.5 115 35.3 2.0 2 mi. E of Obsidian Butte 6/23 8:13 am 33 1.6 117 47.2 2.0 29 mi. SSW of San Clemente 6/23 8:44 am 32 30.1 115 17.2 2.1 16 mi. SE of Calexico 6/23 1:22 pm 33 11.0 115 35.3 2.0 2 mi. ENE of Obsidian Butte 6/23 3:47 pm 34 4.4 117 17.7 2.2 2 mi. S of San Bernardino 6/23 8:25 pm 35 59.0 117 39.9 2.1 16 mi. ESE of Coso Junction 6/23 8:59 pm 35 35.7 118 21.9 2.4 6 mi. ESE of town of Lake Isabella 6/23 9:48 pm 35 16.5 118 35.7 3.4 13 mi. NW of Tehachapi 6/23 9:52 pm 35 16.4 118 35.7 2.2 " 6/23 11:07 pm 34 0.2 116 51.6 2.3 5 mi. N of Banning 6/24 1:06 am 34 1.4 116 25.9 2.1 5 mi. NE of Desert Hot Springs 6/24 9:50 am 32 12.8 115 47.7 2.5 35 mi. SSW of Calexico 6/24 10:44 am 32 39.8 118 7.8 2.3 16 mi. SE of San Clemente Is. (SE tip) 6/24 1:28 pm 35 47.5 117 38.0 2.0 11 mi. N of Ridgecrest 6/24 1:56 pm 33 49.2 116 37.9 2.2 4 mi. W of Palm Springs 6/24 4:03 pm 36 37.6 119 18.6 2.5 20 mi. N of Visalia 6/24 5:55 pm 33 10.5 115 35.4 2.4 2 mi. E of Obsidian Butte 6/24 10:04 pm 34 3.0 117 13.8 2.2 1 mi. E of Loma Linda 6/24 11:37 pm 33 15.7 116 0.4 2.2 2 mi. WSW of Salton City 6/25 1:44 am 34 24.1 116 28.1 2.1 19 mi. N of Yucca Valley 6/25 1:45 am 34 24.3 116 28.5 2.0 " 6/25 7:42 am 34 11.3 116 48.1 2.3 6 mi. NNE of Mt. San Gorgonio 6/25 4:11 pm 35 58.8 117 40.5 2.3 15 mi. ESE of Coso Junction -------------------------------------------------------------