SOUTHERN CALIFORNIA
SEISMOGRAPHIC NETWORK
A Cooperative Project of
Caltech and the U.S. Geological Survey
October 9, 1997
Weekly Earthquake Report for Southern California
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October 2 - 8, 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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If you receive this Report by FAX and if you have recently had
a change of AREA CODE, please notify us ASAP. We have no other
way to know which fax numbers need to be changed!! Actually, if
your area code is 818 and it HASN'T changed, it would be helpful
to know that, too.
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This week's Report covers the time period from midnight Thursday
morning, October 2, Universal Time (ie. UTC), to midnight
Wednesday night, October 8, Universal Time. In local time,
the period of coverage is from 5 p.m., October 1, Pacific
Daylight Time, to 5 p.m., October 8, Pacific Daylight Time. We
detected 219 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
Aside from the two M3 events in Parkfield, for which
the reader should refer to the Northern California Earthquake
Report, there were three M3+ quakes in our region this week.
The first occurred on Friday night in the San Gabriel Mtns.,
between San Fernando and Elizabeth Lake (eight miles away from
the San Andreas Fault). It has a magnitude of M3.1 and a
strike-slip focal mechanism, with a north-south or east-west
fault plane. (Remember that the seismological focal mechanism
is always ambiguous, unless you know something else about the
quake; there are always two possible fault planes.) Because
the epicentral area is unpopulated, there were no 'felt' reports.
The second event was in the late morning on Monday,
in Death Valley. It had a magnitude of M3.4, making it the
largest quake of the week. Our network is sparse in that region;
however, the focal mechanism is consistent with strike-slip
at an strike similar to mapped faults in the area.
The third M3 (M3.1 to be exact) occurred the same day,
in the afternoon, and was a Northridge aftershock. It had a
thrust mechanism and was widely felt in San Fernando Valley and
Hollywood.
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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10/1 5:23 pm 36 5.9 117 53.6 2.3 4 mi. NE of Coso Junction
10/1 9:52 pm 35 47.2 116 38.6 2.0 24 mi. WSW of Shoshone
10/2 1:34 am 34 20.7 116 27.7 2.3 15 mi. N of Yucca Valley
10/2 2:22 am 35 47.2 117 39.6 2.0 11 mi. N of Ridgecrest
10/2 11:33 am 34 15.5 119 22.4 2.6 4 mi. WSW of Ventura
10/2 4:27 pm 33 4.1 115 34.9 2.0 3 mi. NE of Westmorland
10/2 9:36 pm 32 47.6 115 26.6 2.4 6 mi. E of El Centro
10/2 11:28 pm 36 6.8 117 52.1 2.0 6 mi. NE of Coso Junction
10/3 3:49 am 33 11.8 115 34.0 2.1 3 mi. SW of Niland
10/3 9:41 am 34 21.3 116 27.6 2.2 16 mi. N of Yucca Valley
10/3 3:02 pm 32 42.8 115 54.5 2.0 5 mi. ESE of Ocotillo
10/3 8:52 pm 34 8.6 117 20.1 2.5 3 mi. NE of Rialto
10/3 8:55 pm 36 4.2 119 51.0 2.5 28 mi. E of Coalinga
10/3 10:10 pm 34 30.0 118 19.4 3.1 11 mi. SSE of Elizabeth
Lake
10/4 1:41 am 33 42.2 116 50.8 2.2 7 mi. ESE of Hemet
10/4 12:36 pm 34 38.9 116 31.1 2.9 28 mi. ENE of Lucerne
Valley
10/4 2:08 pm 34 20.5 116 28.2 2.3 15 mi. N of Yucca Valley
10/5 12:06 am 34 6.8 117 19.8 2.2 2 mi. WNW of San
Bernardino
10/5 7:06 am 34 16.9 116 46.0 2.3 5 mi. ENE of Big Bear City
10/5 7:37 am 33 33.9 118 20.7 2.1 10 mi. SSW of Pt. Fermin,
San Pedro
10/5 7:55 am 34 10.2 117 19.6 2.1 4 mi. NNW of San
Bernardino
10/5 9:08 am 33 41.7 117 59.4 2.4 2 mi. SW of Fountain
Valley
10/5 4:10 pm 33 46.9 116 58.9 2.1 2 mi. NNW of Hemet
10/5 4:28 pm 35 57.3 120 31.5 3.0 6 mi. NW of Parkfield
10/6 8:07 am 34 28.1 116 30.9 2.2 24 mi. N of Yucca Valley
10/6 11:29 am 35 46.8 116 38.8 3.4 24 mi. WSW of Shoshone
10/6 2:27 pm 34 15.9 118 28.3 3.1 1 mi. ESE of Granada Hills
FELT in S.F. Valley,
Hollywood
10/7 7:36 pm 35 58.0 117 58.6 2.2 5 mi. SSW of Coso Junction
10/7 8:25 pm 33 1.1 117 51.0 2.1 31 mi. SSW of Dana Point
10/7 8:34 pm 35 56.2 120 32.2 3.1 6 mi. WNW of Parkfield
10/8 1:24 am 33 41.9 115 57.0 2.1 11 mi. N of North Shore
10/8 9:59 am 33 33.1 118 7.8 2.1 10 mi. SSW of Bolsa Chica
Beach
10/8 1:10 pm 33 30.3 116 26.4 2.0 15 mi. S of Palm Desert
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