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1995-04-19
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April 13, 1995
Weekly Earthquake Report for Southern California
------------------------------------------------
April 6 - 12, 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, April 6, Pacific Daylight Time, to midnight
Wednesday night, April 12, 1995, Pacific Daylight Time. We
recorded 271 earthquakes of M1.0 or larger during the 7-day
period covered.
There were four M3+ quakes this week, all of them
aftershocks of the June 28, 1992 Landers quake. The largest
one, M3.7, occurred early Monday morning. It might have been
felt, even though it was in a fairly unpopulated area; however,
we got no calls. Its focal mechanism showed strike-slip
faulting, like most of the Landers aftershocks. Last Thursday
evening, there was a M3.1 in the same general vicinity, also
apparently unnoticed by the public. On Sunday afternoon, a M3.3
nearer to Yucca Valley was felt, as was a M3.4 on Tuesday morning.
The latter was near the southern end of the Landers aftershock
zone. Its focal mechanism showed northeast-striking normal
faulting. This type of mechanism was common in all of the Little
San Bernardino Mountains before the Joshua Tree earthquake and is
similar to the mechanism of the M3.2 earthquake that occurred west
of the Landers/Joshua Tree aftershock zone on March 27.
This week, the largest Northridge aftershock was only
M2.3. Since the Northridge mainshock (Mw6.7) was quite a bit
smaller than the Landers aftershock (Mw7.3), the former's after-
shocks have overall been fewer and have been dying off more
quickly. We have already passed the point in time when the
weekly rate of Landers aftershocks is higher than that of
Northridge. Recent Weekly Reports have been reflecting this
trend. Given the present rates of aftershocks and their rates
of decay, we expect the Landers sequence to be noticeable on our
maps for another five years, while Northridge may have returned
to the background rate in another two years.
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
-------------------------------------------------------------
4/6 1:32 am 33 48.8 116 11.9 2.5 6 mi. N of Indio
4/6 11:38 am 35 4.9 119 4.0 2.8 7 mi. NW of the I5/99
interchange/Grapevine
4/6 11:39 am 35 4.8 119 5.0 2.1 "
4/6 5:22 pm 35 49.3 117 45.7 2.4 14 mi. NNW of Ridgecrest
4/6 7:01 pm 34 12.0 116 26.0 2.2 5 mi. N of Yucca Valley
4/6 7:04 pm 32 28.7 115 49.5 2.0 20 mi. SSE of Ocotillo
4/6 8:17 pm 34 21.9 116 28.2 3.1 17 mi. N of Yucca Valley
4/6 11:38 pm 34 12.2 118 38.2 2.0 1 mi. W of Canoga Park
4/7 5:50 am 35 58.6 117 18.8 2.4 14 mi. NNE of Trona
4/7 9:51 am 34 37.4 116 36.0 2.0 23 mi. ENE of Lucerne
Valley
4/7 11:00 am 34 23.2 118 37.2 2.0 3 mi. SW of Magic Mtn.
4/7 2:30 pm 34 37.9 116 30.4 2.4 28 mi. ENE of Lucerne
Valley
4/7 4:20 pm 35 43.5 118 29.5 2.3 6 mi. NNW of the town of
Lake Isabella
4/7 4:52 pm 33 0.6 116 5.4 2.1 9 mi. SSE of Ocotillo
Wells
4/7 8:06 pm 34 16.7 119 57.5 2.3 10 mi. SSW of Isla Vista
4/7 8:41 pm 33 11.6 115 33.9 2.2 4 mi. SW of Niland
Obsidian Butte
4/7 9:07 pm 34 17.1 119 56.9 2.0 10 mi. SSW of Isla Vista
4/8 2:27 am 34 16.2 119 56.6 2.4 "
4/8 9:29 am 34 24.8 116 28.4 2.3 20 mi. N of Yucca Valley
4/8 1:19 pm 34 22.3 116 28.1 2.1 17 mi. N of Yucca Valley
4/8 5:17 pm 33 10.3 115 37.0 2.0 6 mi. WNW of Calipatria
4/8 10:45 pm 36 15.2 120 16.2 2.5 9 mi. NNE of Coalinga
4/9 5:26 am 34 7.2 116 55.1 2.4 5 mi. WNW of Mt. San
Gorgonio
4/9 4:01 pm 34 2.4 116 19.3 3.3 8 mi. SE of Yucca Valley
FELT
4/9 7:46 pm 34 17.1 118 27.3 2.3 1 mi. WNW of San Fernando
4/9 7:55 pm 35 55.9 117 40.0 2.5 17 mi. ESE of Coso Junction
Coso Range
4/9 7:56 pm 35 55.9 117 40.0 2.7 "
4/9 9:57 pm 33 11.5 115 36.4 2.3 6 mi. WSW of Niland
Obsidian Butte
4/9 10:02 pm 33 11.4 115 36.8 2.9 "
4/9 11:58 pm 34 59.2 116 57.2 2.2 7 mi. NNE of Barstow
4/10 1:17 am 33 11.6 115 35.4 2.0 5 mi. SW of Niland
Obsidian Butte
4/10 2:26 am 33 11.4 115 35.5 2.0 "
4/10 2:41 am 34 10.1 116 26.2 2.0 3 mi. N of Yucca Valley
4/10 7:01 am 34 24.7 116 28.2 3.7 20 mi. N of Yucca Valley
4/10 7:10 am 36 1.7 118 13.4 2.0 15 mi. W of Coso Junction
Coso Range
4/10 9:27 am 34 28.5 116 29.7 2.1 24 mi. N of Yucca Valley
4/10 11:42 am 34 59.0 116 56.8 2.5 7 mi. NNE of Barstow
4/10 1:26 pm 34 14.8 118 29.0 2.1 2 mi. ENE of Northridge
4/10 5:00 pm 33 20.3 116 14.6 2.3 9 mi. NE of Borrego
Springs
4/11 2:27 am 34 23.1 116 27.4 2.0 18 mi. N of Yucca Valley
4/11 3:06 am 34 22.3 116 27.2 2.2 "
4/11 8:56 am 33 54.4 116 17.5 3.4 13 mi. NNW of Indio; FELT
4/11 10:30 am 34 22.1 116 27.5 2.1 17 mi. N of Yucca Valley
4/11 11:45 am 34 21.7 116 27.5 2.1 "
4/11 6:55 pm 36 5.5 117 40.2 2.6 15 mi. ESE of Haiwee Reservoir
Coso Range
4/12 3:23 am 33 54.4 116 17.5 2.5 13 mi. NNW of Indio
4/12 8:47 pm 34 18.3 118 25.6 2.1 1 mi. NNE of San Fernando
4/12 8:52 pm 33 32.9 115 54.3 2.4 2 mi. NE of North Shore
4/12 10:07 pm 34 56.5 116 46.7 2.0 14 mi. ENE of Barstow
4/12 11:53 pm 35 18.3 118 30.6 2.6 12 mi. NNW of Tehachapi
-------------------------------------------------------------