SOUTHERN CALIFORNIA
SEISMOGRAPHIC NETWORK
A Cooperative Project of
Caltech and the U.S. Geological Survey
September 4, 1997
Weekly Earthquake Report for Southern California
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August 28 - September 3, 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 626-395-6327. For daily
updates, call our Earthquake Information Hotline: 626-395-6977.
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This week's Report covers the time period from midnight Thursday
morning, August 28, Universal Time (ie. UTC), to midnight
Wednesday night, September 3, Universal Time. In local time,
the period of coverage is from 5 p.m., August 27, Pacific Daylight
Time, to 5 p.m., September 3, Pacific Daylight Time. We detected
218 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 largest quake of the week was a M3.5 in the
Tehachapi Mtns. near Lake Isabella. It occurred on Sunday
evening and attracted no attention from the public. It had a
mostly strike-slip focal mechanism.
There were two smaller quakes that were felt. The first
was a member of the on-going cluster in the Cajon Pass. It has
a magnitude of M3.1 and occurred early Tuesday morning. Like the
other cluster members, this quake had a 'normal' or tensional
focal mechanism, associated with the graben that forms the
San Bernardino Basin between the San Andreas and San Jacinto
Faults.
The other felt quake occurred on Tuesday evening, in
the channel between Orange County and Catalina Island. It was
a M3.1 that was felt in Avalon. The focal mechanism is poorly
determined, since our network is sparse in the offshore areas
and because the onset of this quake was 'emergent', but the
mechanism is probably thrust.
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
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Date Time N Lat. W Long. Mag
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8/28 12:44 am 34 20.4 116 28.4 2.3 15 mi. N of Yucca Valley
8/28 12:20 pm 35 47.0 117 36.6 2.2 11 mi. NNE of Ridgecrest
8/29 12:04 am 32 39.2 115 55.4 2.1 6 mi. SE of Ocotillo
8/29 7:48 am 32 38.7 115 54.9 2.3 7 mi. SE of Ocotillo
8/29 11:31 am 32 39.0 115 55.3 2.3 "
8/29 12:16 pm 34 9.4 117 20.4 2.0 3 mi. NNE of Rialto
8/29 7:09 pm 35 14.9 114 58.1 2.2 34 mi. NW of Needles
8/30 5:00 am 34 18.1 118 25.7 2.5 1 mi. NNE of San Fernando
8/30 5:00 am 34 18.4 118 25.5 2.5 "
(yes, there were two)
8/30 6:51 am 35 43.4 118 17.3 2.3 11 mi. ENE of town of Lake
Isabella
8/30 8:40 am 36 26.6 117 2.2 2.1 10 mi. W of Furnace Creek
8/30 3:39 pm 34 54.1 116 55.6 2.7 5 mi. E of Barstow
8/31 1:31 am 32 38.1 115 55.2 2.3 8 mi. SSE of Ocotillo
8/31 12:19 pm 32 9.9 115 40.3 2.9 36 mi. SSW of Calexico
8/31 5:36 pm 35 27.0 118 26.0 3.5 13 mi. S of town of Lake
Isabella
8/31 7:36 pm 32 10.0 115 39.6 2.6 36 mi. SSW of Calexico
9/1 3:12 pm 33 9.6 115 38.5 2.2 Underneath Obsidian Butte
9/1 3:15 pm 33 10.1 115 38.2 2.2 "
9/2 6:47 am 34 9.0 117 20.1 3.1 3 mi. NE of Rialto; FELT
9/2 8:32 am 34 8.8 117 19.9 2.7 3 mi. NW of San Bernardino
9/2 8:47 am 33 21.1 116 22.7 2.1 6 mi. N of Borrego Springs
9/2 5:49 pm 36 1.7 117 45.9 2.5 10 mi. E of Coso Junction
9/2 8:46 pm 33 27.6 118 11.7 3.1 10 mi. NE of Avalon,
Catalina Island; FELT
9/3 3:03 am 33 14.3 119 9.7 2.5 17 mi. SSW of Santa
Barbara Is.
9/3 8:19 am 33 53.2 118 36.1 2.2 11 mi. SSE of Malibu
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