SOUTHERN CALIFORNIA
SEISMOGRAPHIC NETWORK
A Cooperative Project of
Caltech and the U.S. Geological Survey
September 5, 1996
Weekly Earthquake Report for Southern California
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August 29 - September 4, 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.
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This week's Report covers the time period from midnight Thursday
morning, August 29, Universal Time (ie. GMT), to midnight Wednesday
night, September 4, Universal Time. In local time, the period of
coverage is from 5 p.m., August 28, Pacific Daylight Time, to
5 p.m., September 4, Pacific Daylight Time. We detected and
processed 409 earthquakes during the seven-day period covered.
This week's seismicity showed an increase over recent
weeks, although, of course, it is still within expected statistical
fluctuations. The largest event (M4.0) occurred last Thursday
evening, south of the U.S./Mexico border, but it was felt in the
Imperial Valley area.
Most of the increased activity this week is accounted
for by a swarm in the Coso Range, east of Haiwee Reservoir.
This swarm started on Tuesday morning and culminated with a M3.5
in the wee hours of the morning on Wednesday. Following the M3.5,
the seismicity rate slowed down but has not gone away entirely,
as of the writing of this report (Thursday morning). The Coso
Range is a seismic and geothermal area north and east of
Ridgecrest, where large swarms occurred late last year and early
this year. The M3.5 showed north-striking normal faulting. Both
normal and strike-slip faulting are common in this extensional
region.
Also on Wednesday morning, about an hour and a half after
the Coso M3.5, a M3.2 occurred in the Mojave Desert near Boron.
This earthquake showed strike-slip faulting, by far the most
common type of faulting in the Mojave desert. It produced only
three tiny aftershocks. This activity is clearly separate from
the Landers aftershock zone.
There was also a Barstow event, which was a Landers
aftershock, on Wednesday afternoon. It has a magnitude of M3.3.
As for all of the Barstow aftershocks, this one showed
right-lateral strike-lip on a northwest-striking fault. If any of
this activity Tuesday and Wednesday was felt by the public, we got
no inquiries.
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 7:05 pm 33 28.5 116 31.1 2.2 10 mi. ESE of Anza
8/28 7:05 pm 33 28.6 116 31.5 2.3 "
8/28 7:07 pm 33 28.5 116 31.0 2.3 "
8/28 8:36 pm 32 21.6 115 20.7 2.1 21 mi. SSE of Calexico
8/29 11:24 pm 32 22.5 115 22.7 4.0 " FELT
8/29 11:31 pm 32 22.4 115 22.4 2.0 "
8/29 11:40 pm 32 21.4 115 22.4 2.2 "
8/30 5:10 am 32 22.5 115 21.6 3.0 "
8/30 5:31 am 32 22.8 115 21.8 2.1 "
8/30 4:41 pm 35 19.7 116 23.2 2.6 18 mi. WNW of Baker
8/31 5:45 am 34 22.9 116 27.3 2.4 18 mi. N of Yucca Valley
8/31 10:29 am 34 55.8 116 41.4 2.0 19 mi. E of Barstow
8/31 1:16 pm 35 58.5 117 39.0 2.1 17 mi. ESE of Coso
Junction
8/31 4:36 pm 32 22.6 115 22.5 2.7 21 mi. SSE of Calexico
9/1 12:39 am 34 2.0 117 15.7 2.4 1 mi. SSW of Loma Linda
9/1 6:15 am 34 30.5 116 32.0 2.7 27 mi. N of Yucca Valley
9/1 8:47 am 34 56.5 116 48.0 2.6 13 mi. ENE of Barstow
9/1 9:31 am 34 17.6 118 27.6 2.0 1 mi. WNW of Pacoima
9/1 1:34 pm 35 44.7 117 37.3 3.0 8 mi. NNE of Ridgecrest
9/1 2:09 pm 35 44.6 117 37.4 2.2 "
9/1 7:56 pm 34 2.4 117 11.3 2.5 1 mi. SSW of Redlands
9/2 9:17 am 34 28.4 116 30.4 2.2 24 mi. N of Yucca Valley
9/2 12:02 pm 36 9.9 120 6.6 2.3 14 mi. E of Coalinga
9/2 12:43 pm 32 59.9 117 44.1 2.1 24 mi. WSW of Oceanside
9/2 1:04 pm 33 10.1 115 38.3 2.3 Under Obsidian Butte
9/2 5:49 pm 34 20.3 116 28.5 2.2 15 mi. N of Yucca Valley
9/2 5:56 pm 32 16.6 115 14.1 2.6 31 mi. SSE of Calexico
9/3 12:27 am 34 19.1 116 27.8 2.5 13 mi. N of Yucca Valley
9/3 12:50 am 35 1.3 119 11.3 2.2 13 mi. W of Wheeler Ridge
9/3 1:41 am 34 23.5 116 27.6 2.2 18 mi. N of Yucca Valley
9/3 6:02 am 34 18.0 116 27.1 2.1 12 mi. N of Yucca Valley
9/3 6:59 am 36 7.0 117 50.9 2.2 Coso Range, 5 mi. ESE of
Haiwee Reservoir
9/3 7:05 am 36 6.8 117 51.3 2.4 "
9/3 7:06 am 36 6.5 117 50.9 2.2 "
9/3 7:08 am 36 6.9 117 51.0 2.2 "
9/3 8:26 am 36 6.6 117 51.1 2.0 "
9/3 8:27 am 36 6.3 117 51.0 2.1 "
9/3 8:30 am 36 6.5 117 51.3 2.8 "
9/3 9:05 am 36 6.5 117 51.2 2.5 "
9/3 9:57 am 36 6.7 117 51.3 2.6 "
9/3 10:02 am 36 6.6 117 50.9 2.5 "
9/3 6:31 pm 36 6.0 117 51.6 2.2 "
9/3 10:07 pm 36 6.6 117 51.2 2.1 "
9/4 1:09 am 36 5.9 117 51.8 2.3 "
9/4 1:17 am 36 6.9 117 50.8 2.1 "
9/4 1:31 am 35 45.2 117 38.1 2.0 9 mi. NNE of Ridgecrest
9/4 1:39 am 36 7.2 117 51.0 2.6 5 mi. ESE of Haiwee
Reservoir
9/4 2:00 am 36 7.0 117 51.3 3.5 "
9/4 3:32 am 35 6.1 117 29.7 3.2 11 mi. NE of Boron
9/4 3:52 am 36 6.8 117 51.3 2.3 5 mi. ESE of Haiwee
Reservoir
9/4 3:53 am 36 6.8 117 50.9 2.1 "
9/4 4:05 am 36 6.2 117 51.5 2.6 "
9/4 7:06 am 36 6.5 117 50.8 2.1 "
9/4 9:10 am 36 7.3 117 51.0 2.4 "
9/4 9:35 am 34 15.8 116 36.8 2.2 15 mi. N of Morongo
Valley
9/4 10:11 am 36 6.4 117 51.2 2.0 5 mi. ESE of Haiwee
Reservoir
9/4 2:28 pm 36 6.9 117 50.8 2.0 "
9/4 3:48 pm 34 58.7 116 57.1 3.3 7 mi. NNE of Barstow
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