SOUTHERN CALIFORNIA
SEISMOGRAPHIC NETWORK
A Cooperative Project of
Caltech and the U.S. Geological Survey
August 24, 1995
Weekly Earthquake Report for Southern California
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August 17 - 23, 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, August 17, Pacific Daylight Time, to midnight
Wednesday night, August 23, 1995, Pacific Daylight Time. We
recorded 1,568 earthquakes of during the 7-day period covered.
The biggest excitement of the week was the M5.4 that
occurred last Thursday afternoon, north of Ridgecrest. It was
felt as far away as the L.A. area to the south, and Bishop to
the north. The mechanism was mostly "normal" (dip slip with
extension of the crust), with a component of strike-slip,
right in line with what we know about the area. The second figure
shows a map view and a cross section, which clearly shows the
dipping fault. Glenn Roquemore and Kerry Sieh believe this to
be part of the Airport Lake fault system.
The earthquake produced a robust aftershock sequence,
that is dying off in a predictable manner. The rate of decay is
close to the average rate of California earthquakes. There are,
however, relatively more small aftershocks compared to the number
of large ones. This leads to a slope of the magnitude-frequency
distribution (called the b-value) of about 1.2, higher than the
California averge of 0.9 (The highest ever seen in a California
aftershock sequence is 1.4, the 1986 Oceanside sequence.). The
tally for the sequence so far is 1,294 events. Since Mother
Nature was kind to us by allowing almost a week to process the
data, these figures are more reliable than what sometimes appears
for the early days of a sequence.
Because the sequence is decaying at a normal rate, and
because almost one week has already passed since the mainshock,
coupled with the relatively few larger aftershocks, the
probability of further large aftershocks is small. The chances
of another M4.5 or greater is less than 10%.
Eclipsed but not forgotten, a M3.2 was felt in Barstow
earlier on August 17th. It was an aftershock of the June 28,
1992 Landers earthquake.
The table lists the quakes this week that were M2.0 or
larger in the central part of the coverage area. Only quakes
M2.5 or larger are listed for the Ridgecrest sequence. 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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8/17 5:34 am 33 12.7 115 38.6 2.5 2 mi. N of Obsidian Butte
8/17 6:55 am 34 8.9 116 26.3 2.2 2 mi. NNE of Yucca Valley
8/17 8:06 am 34 20.6 118 34.1 2.4 3 mi. S of Valencia
8/17 8:26 am 34 55.9 116 54.9 3.2 6 mi. ENE of Barstow
FELT
8/17 11:12 am 34 19.7 116 50.8 2.4 4 mi. N of Big Bear City
8/17 12:47 pm 34 12.1 117 36.6 2.1 6 mi. SSE of Mt. Baldy
8/17 3:39 pm 35 46.6 117 39.7 5.4 10 mi. N of Ridgecrest
FELT
8/17 3:41 pm 35 47.4 117 40.7 4.2 11 mi. N of Ridgecrest
8/17 3:43 pm 35 47.0 117 39.8 3.9 "
8/17 3:47 pm 35 47.5 117 40.2 2.5 "
8/17 3:49 pm 35 47.2 117 40.5 2.8 "
8/17 3:49 pm 35 46.9 117 40.7 3.2 "
8/17 3:55 pm 35 46.6 117 40.1 2.7 10 mi. N of Ridgecrest
8/17 3:59 pm 35 45.9 117 40.1 2.6 9 mi. N of Ridgecrest
8/17 3:59 pm 35 45.8 117 40.2 2.5 "
8/17 3:59 pm 35 46.2 117 40.3 2.6 10 mi. N of Ridgecrest
8/17 4:03 pm 35 45.8 117 39.0 2.7 9 mi. N of Ridgecrest
8/17 4:06 pm 35 47.0 117 39.3 2.5 11 mi. N of Ridgecrest
8/17 4:17 pm 35 45.8 117 39.2 2.7 9 mi. N of Ridgecrest
8/17 4:18 pm 35 47.2 117 39.8 2.5 11 mi. N of Ridgecrest
8/17 4:19 pm 35 47.2 117 39.8 2.7 "
8/17 4:28 pm 35 47.2 117 40.0 2.7 "
8/17 4:33 pm 35 45.8 117 39.6 3.6 9 mi. N of Ridgecrest
8/17 4:34 pm 35 46.7 117 40.2 2.7 10 mi. N of Ridgecrest
8/17 4:36 pm 35 46.6 117 40.4 3.2 "
8/17 4:37 pm 35 46.0 117 39.8 2.5 "
8/17 4:43 pm 35 46.9 117 40.4 3.0 11 mi. N of Ridgecrest
8/17 4:45 pm 35 46.4 117 39.3 2.5 10 mi. N of Ridgecrest
8/17 4:46 pm 35 47.0 117 40.1 2.7 11 mi. N of Ridgecrest
8/17 4:46 pm 35 48.2 117 40.7 2.9 12 mi. N of Ridgecrest
8/17 4:54 pm 35 45.8 117 39.1 2.7 9 mi. N of Ridgecrest
8/17 4:59 pm 35 46.8 117 39.5 3.0 11 mi. N of Ridgecrest
8/17 5:05 pm 35 46.3 117 39.5 2.7 10 mi. N of Ridgecrest
8/17 5:10 pm 35 46.3 117 39.3 2.6 "
8/17 5:29 pm 35 46.3 117 39.3 3.0 "
8/17 5:40 pm 35 46.1 117 39.3 2.5 "
8/17 5:42 pm 35 45.8 117 39.7 2.5 9 mi. N of Ridgecrest
8/17 6:00 pm 35 46.1 117 39.3 2.5 10 mi. N of Ridgecrest
8/17 6:10 pm 34 1.6 118 58.9 2.0 2 mi. WSW of Leo Carrillo
State Beach
8/17 6:51 pm 35 46.3 117 39.2 2.5 10 mi. N of Ridgecrest
8/17 6:56 pm 35 47.4 117 39.8 3.2 11 mi. N of Ridgecrest
8/17 7:01 pm 35 46.3 117 39.0 2.7 10 mi. N of Ridgecrest
8/17 7:05 pm 35 47.4 117 39.9 2.6 11 mi. N of Ridgecrest
8/17 7:11 pm 35 46.3 117 40.1 2.8 10 mi. N of Ridgecrest
8/17 7:12 pm 35 47.3 117 39.7 2.5 11 mi. N of Ridgecrest
8/17 7:33 pm 35 47.0 117 39.9 3.3 "
8/17 8:08 pm 35 47.4 117 39.7 2.5 "
8/17 8:13 pm 35 47.0 117 40.0 2.7 "
8/17 8:22 pm 35 47.0 117 39.8 3.1 "
8/17 8:27 pm 35 47.2 117 40.0 2.6 "
8/17 8:28 pm 35 47.0 117 39.7 2.5 "
8/17 8:33 pm 35 46.0 117 39.4 2.7 10 mi. N of Ridgecrest
8/17 8:34 pm 35 46.0 117 39.3 2.5 "
8/17 8:37 pm 35 46.5 117 39.1 2.6 "
8/17 8:51 pm 35 46.2 117 39.2 3.5 "
8/17 9:54 pm 35 46.4 117 40.0 3.0 "
8/17 10:03 pm 35 47.2 117 39.4 3.5 11 mi. N of Ridgecrest
8/17 11:26 pm 32 42.2 117 33.7 2.2 18 mi. WSW of Mission
Beach
8/17 11:50 pm 35 47.0 117 40.3 3.1 11 mi. N of Ridgecrest
8/18 1:37 am 35 45.8 117 39.7 2.5 9 mi. N of Ridgecrest
8/18 2:03 am 35 45.7 117 39.2 2.5 "
8/18 2:15 am 35 47.3 117 38.6 2.9 11 mi. N of Ridgecrest
8/18 2:45 am 33 26.3 117 3.7 2.0 11 mi. ENE of Fallbrook
8/18 3:00 am 34 16.2 116 26.5 2.4 10 mi. N of Yucca Valley
8/18 4:31 am 35 46.9 117 39.6 2.7 11 mi. N of Ridgecrest
8/18 5:13 am 35 46.4 117 40.0 3.0 10 mi. N of Ridgecrest
8/18 5:29 am 35 46.5 117 40.0 2.5 "
8/18 7:16 am 35 46.5 117 38.3 2.7 "
8/18 7:18 am 35 46.5 117 38.3 2.6 "
8/18 7:24 am 35 47.0 117 39.5 2.6 11 mi. N of Ridgecrest
8/18 7:58 am 35 46.1 117 39.4 2.6 10 mi. N of Ridgecrest
8/18 8:57 am 35 46.5 117 38.2 2.5 "
8/18 10:07 am 35 46.0 117 39.5 2.5 9 mi. N of Ridgecrest
8/18 12:11 pm 35 45.3 117 39.4 3.0 "
8/18 1:53 pm 35 46.4 117 39.5 2.5 10 mi. N of Ridgecrest
8/18 3:13 pm 35 46.1 117 39.2 2.5 "
8/18 4:07 pm 35 46.1 117 39.0 2.5 "
8/18 8:54 pm 35 45.0 117 38.8 2.8 8 mi. N of Ridgecrest
8/18 9:01 pm 33 24.2 116 26.0 3.2 10 mi. NNW of Borrego
Springs
8/19 5:11 am 35 46.7 117 39.0 3.2 10 mi. N of Ridgecrest
8/19 6:29 am 32 57.2 117 45.0 2.2 27 mi. SW of Oceanside
8/19 6:59 am 35 46.6 117 38.7 2.6 10 mi. N of Ridgecrest
8/19 7:29 am 35 46.3 117 39.1 2.5 "
8/19 8:52 am 35 46.5 117 38.6 2.5 "
8/19 5:46 pm 35 46.8 117 39.2 2.5 "
8/19 7:30 pm 35 46.5 117 38.8 2.7 "
8/19 8:26 pm 35 46.6 117 39.1 2.5 "
8/19 11:28 pm 35 45.6 117 40.5 2.7 9 mi. N of Ridgecrest
8/20 12:16 am 34 35.5 116 36.6 2.3 21 mi. ENE of Lucerne
Valley
8/20 2:17 am 35 28.5 120 45.3 2.6 4 mi. W of Atascadero
8/20 2:31 am 34 50.1 117 13.2 2.4 11 mi. WSW of Barstow
8/20 9:23 am 33 24.2 116 26.3 2.8 10 mi. NNW of Borrego
Springs
8/20 11:42 am 35 27.6 120 46.0 2.4 5 mi. WSW of Atascadero
8/20 12:39 pm 35 47.4 117 38.1 2.6 11 mi. N of Ridgecrest
8/20 2:07 pm 34 54.7 117 23.6 2.1 21 mi. W of Barstow
8/20 7:43 pm 35 46.2 117 39.7 2.5 10 mi. N of Ridgecrest
8/20 8:07 pm 35 47.1 117 39.9 2.8 11 mi. N of Ridgecrest
8/20 9:44 pm 35 46.7 117 39.0 2.5 10 mi. N of Ridgecrest
8/21 3:15 am 34 25.7 116 31.0 2.0 21 mi. N of Yucca Valley
8/21 6:09 am 34 22.4 116 27.9 2.3 17 mi. N of Yucca Valley
8/21 8:02 am 35 47.5 117 40.0 2.6 11 mi. N of Ridgecrest
8/21 9:42 am 35 47.6 117 40.0 2.6 "
8/21 12:52 pm 35 45.7 117 39.4 2.6 9 mi. N of Ridgecrest
8/22 8:01 am 33 10.4 115 36.6 2.5 1 mi. E of Obsidian Butte
8/22 8:08 am 33 10.5 115 36.1 2.4 2 mi. E of Obsidian Butte
8/22 9:20 am 34 37.9 116 39.1 2.2 21 mi. NE of Lucerne
Valley
8/22 9:26 am 33 10.6 115 36.5 2.8 1 mi. ENE of Obsidian
Butte
8/22 9:57 am 33 40.8 116 43.5 2.2 4 mi. S of Idyllwild
8/22 10:14 am 33 10.6 115 36.3 2.6 1 mi. ENE of Obsidian
Butte
8/23 12:57 am 35 46.5 117 39.3 3.4 10 mi. N of Ridgecrest
8/23 4:13 am 34 53.1 117 44.7 2.0 20 mi. SE of California
City
8/23 8:49 am 33 35.6 117 16.4 2.3 6 mi. SSE of Lake Elsinore
8/23 12:11 pm 33 30.7 116 30.3 2.2 10 mi. ESE of Anza
8/23 8: 8 pm 34 36.4 116 37.9 2.2 21 mi. ENE of Lucerne
Valley
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