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1995-01-14
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January 5, 1995
Weekly Earthquake Report for Southern California
------------------------------------------------
December 29, 1994 - January 4, 1995
Prepared by: Kate Hutton, Seismological Laboratory
(kate@bombay.gps.caltech.edu)
Lucy Jones, U.S. Geological Survey
California Institute of Technology
This document is a commentary on current seismic activity. The
earthquakes discussed have been detected and processed
automatically. All epicenters and magnitudes have been reviewed
to exclude obvious blunders; however, they must still be
considered preliminary. 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, December 29, 1994, Pacific Standard Time, to midnight
Wednesday night, January 4, 1995, Pacific Standard Time. We
recorded 269 earthquakes of M1.0 or larger during the 7-day period
covered.
It was another quiet week. There were only two M3+ quakes
in our monitoring area, excluding the two in northern Baja.
The largest event was a M3.3 Northridge aftershock early
Friday morning. It was felt, as was a much smaller event (M2.6)
yesterday (Wednesday) evening. The other M3+ was in the Coso Range
east of Haiwee Reservoir: a M3.0 on Friday morning. The latter was
part of a small swarm, which is a common occurence in the Coso area.
With the New Year, comes the quarterly statistical summary.
1994 was an active year, with a total of 27,349 quakes recorded
(all magnitudes). This is between twice and three times what a
"quiet" year would be. 556 of these were M3.0 or larger, the largest
one being, of course, Mw6.7 (the Northridge earthquake). As of the
end of the year, the breakdown by magnitude of the Northridge
sequence itself was as follows:
All events 11,031
3.0 - 3.9 367
4.0 - 4.9 48
5.0 and up 9
A similar breakdown for the Landers sequence (April 23, 1992 through
the end of 1994) was as follows:
All events 45,000+
3.0 - 3.9 1,474
4.0 - 4.9 158
5.0 and up 21
We still aren't finished with the data processing, hence the lower
limit on the total number of events.
As for the coming year, statistically speaking, the
Northridge sequence should produce about 17 M3's, about two M4's,
and has about a 25% chance of producing another M5. The expected
number of aftershocks for the Landers/Big Bear sequence is similar:
about 32 M3's, about 3 M4's, and about a 25% chance of another M5.
By comparison, the chance of an independent M5+ earthquake somewhere
in southern California (including all the sparsely populated areas)
is about 80%.
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
-------------------------------------------------------------
12/29 9:16 am 33 47.5 117 6.0 2.4 8 mi. WNW of Hemet
12/29 9:45 am 34 19.3 118 46.2 2.0 4 mi. NW of Simi Valley
12/29 10:45 am 34 6.3 116 44.7 2.2 4 mi. E of Mt. San Gorgonio
12/29 1:57 pm 34 20.0 118 49.9 2.0 6 mi. SE of Fillmore
12/29 3:03 pm 33 46.0 116 8.8 2.2 5 mi. NE of Indio
12/29 5:37 pm 34 11.7 116 51.5 2.3 4 mi. S of Big Bear City
12/29 6:22 pm 34 19.5 118 28.4 2.1 3 mi. NNW of San Fernando
12/30 2:03 am 34 19.1 118 24.3 3.3 3 mi. NE of San Fernando; FELT
12/30 7:21 am 34 44.3 120 7.8 2.0 9 mi. N of Solvang
12/30 7:24 am 34 19.4 118 28.1 2.0 3 mi. NNW of San Fernando
12/30 8:22 am 36 7.6 117 50.3 3.0 5 mi. E of Haiwee Reservoir
12/30 8:25 am 36 7.2 117 50.6 2.5 "
12/30 10:08 am 34 21.5 118 39.2 2.2 5 mi. SW of Magic Mtn.
12/30 12:40 pm 36 7.4 117 49.6 2.2 5 mi. E of Haiwee Reservoir
12/30 12:56 pm 36 7.2 117 50.4 2.1 "
12/30 4:07 pm 32 21.9 115 21.6 3.6 22 mi. SSE of Calexico
12/31 1:39 am 34 47.5 116 17.8 2.0 35 mi. SSW of Baker
12/31 3:51 am 34 23.5 119 22.0 2.2 8 mi. NNW of Ventura
12/31 7:21 am 34 27.9 119 21.6 2.7 6 mi. WNW of Ojai
12/31 5:01 pm 33 43.6 118 49.7 2.2 18 mi. S of Pt. Dume
12/31 7:27 pm 34 23.6 119 21.5 2.1 7 mi. WSW of Ojai
1/1 6:05 am 34 15.7 116 27.1 2.1 9 mi. N of Yucca Valley
1/1 7:13 am 34 9.5 116 26.2 2.0 2 mi. N of Yucca Valley
1/1 1:45 pm 33 55.8 117 54.8 2.2 1 mi. NW of Brea
1/1 3:41 pm 33 0.8 116 22.2 2.0 14 mi. ESE of Julian
1/1 8:04 pm 34 14.9 116 25.9 2.2 9 mi. N of Yucca Valley
1/2 12:55 am 35 2.4 116 59.6 2.0 10 mi. N of Barstow
1/2 3:32 am 32 8.6 115 2.7 3.2 44 mi. SE of Calexico
1/2 7:49 am 34 16.1 118 27.6 2.2 1 mi. SW of San Fernando
1/2 7:00 pm 34 0.8 116 19.3 2.3 10 mi. SE of Yucca Valley
1/2 7:23 pm 34 16.2 118 27.9 2.1 1 mi. WSW of San Fernando
1/3 7:37 am 32 16.1 115 19.5 2.6 29 mi. SSE of Calexico
1/3 8:03 am 34 23.9 119 22.3 2.6 7 mi. WSW of Ojai
1/3 4:26 pm 34 27.6 116 31.1 2.9 24 mi. N of Yucca Valley
1/3 6:23 pm 35 2.1 116 60.0 2.3 10 mi. N of Barstow
1/3 6:30 pm 35 59.9 117 47.8 2.6 9 mi. ESE of Coso Junction
1/3 8:05 pm 33 38.9 118 33.5 2.3 11 mi. SW of Palos Verdes
Point
1/3 8:09 pm 34 14.6 118 33.4 2.6 2 mi. NW of Northridge, FELT
-------------------------------------------------------------
Figure 1. A map of southern California showing the earthquakes
recorded during the past week by the Caltech/USGS Seismic
Network. Major faults are marked, as well as the metropolitan
areas of Los Angeles (L.A.), Palm Springs (P.S.), San Diego
(S.D.), and Santa Barbara (S.B.). The circles denote the
earthquakes, the size of the circle indicating the magnitude.