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                        October 6, 1994

        Weekly Earthquake Report for Southern California
        ------------------------------------------------
                 September 29 - October 5, 1994

    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, September 29, Pacific Daylight Time, to midnight Wednesday
    night, October 5, Pacific Daylight Time.  We recorded only 255
    earthquakes of M1.0 or larger this week.
        The most widely felt event this week occurred just south
    of the area shown on the map.  It was a M4.6 in northern Baja,
    about 55 mi. SSE of Mexicali, at 7:00 am on Tuesday morning.
    It was felt as far north as the Imperial Valley and Yuma, Arizona.
    This area is the transition between the East Pacific Rise spreading
    ridge and the southern end of the San Andreas Fault at the Salton
    Sea, and is very active seismically.
        The largest event inside our coverage area was a M3.1 in
    the Solvang area, early Monday morning.  Although it was certainly
    large enough to feel, no-one called us about it.
        The only quake that was reported felt was a M2.7 Northridge
    aftershock on Friday morning.
        Notice the low number of events this week.  Although,
    statistically, the number of quakes varies from week to week,
    a slow overall decline is apparent with the decline of the two
    major aftershock sequences (Landers/Big Bear and Northridge).
    For statistics buffs, we present a summary of the events processed
    so far from these sequences (through September 30):

    Northridge
        ----------
            All events      10,314+
            3.0 - 3.9          409
            4.0 - 4.9           49
            5.0 and up           9

    GMT date    GMT time     Latitude  Longitude  Depth Mag
        1994  1 17  12 30 55.39  34 12.80 -118 32.22  18.40 6.7
        1994  1 17  12 31 57.82  34 16.76 -118 28.43   0.00 5.9
        1994  1 17  12 40 35.71  34 20.49 -118 36.10   0.01 5.2
        1994  1 17  23 33 30.69  34 19.58 -118 41.90   9.83 5.6
        1994  1 18   0 43  8.89  34 22.59 -118 41.89  11.34 5.2
        1994  1 19  21  9 28.61  34 22.71 -118 42.64  14.44 5.1
        1994  1 19  21 11 44.90  34 22.65 -118 37.06  11.33 5.1
        1994  1 29  11 20 35.95  34 18.32 -118 34.76   1.04 5.1
        1994  3 20  21 20 12.26  34 13.88 -118 28.50  13.09 5.3

    We are almost, but not quite, finished with the preliminary
    data processing of the Northridge sequence.

    Landers/Big Bear
        ----------------
            All events      44,117+
            3.0 - 3.9        1,462
            4.0 - 4.9          157
            5.0 and up          21

        GMT date    GMT time     Latitude  Longitude  Depth Mag
        1992  4 23   4 50 23.22  33 57.67 -116 19.05  12.38 6.1
        1992  5 18  15 44 17.97  33 57.06 -116 20.25   6.57 5.0
        1992  6 28  11 57 34.13  34 12.03 -116 26.14   1.03 7.3
        1992  6 28  12  0 45.00  34  7.84 -116 24.49   0.01 5.6
        1992  6 28  12  1 16.19  34  7.19 -116 19.39   6.00 5.4
        1992  6 28  12 36 40.64  34  8.09 -116 26.06   7.39 5.3
        1992  6 28  12 40 53.82  34 19.83 -116 32.84   6.00 5.4
        1992  6 28  14 43 21.85  34  9.71 -116 51.13  11.06 5.5
        1992  6 28  15  5 30.73  34 12.16 -116 49.61   5.32 6.2
        1992  6 28  17  1 31.92  34 10.71 -116 55.35  13.72 5.1
        1992  6 28  17  5 57.56  34 15.31 -116 54.72   7.66 5.0
        1992  6 29  14  8 37.73  34  6.27 -116 24.19  10.35 5.5
        1992  6 29  14 13 38.78  34  6.49 -116 24.23   9.88 5.0
        1992  7  1   7 40 29.90  34 19.84 -116 27.76   8.28 5.3
        1992  7  5  21 18 27.14  34 34.95 -116 19.07   0.11 5.4
        1992  8 17  20 41 52.12  34 11.70 -116 51.76  11.27 5.0
        1992  9 15   8 47 11.29  34  3.82 -116 21.64   8.30 5.1
        1992 11 27  16  0 57.49  34 20.40 -116 54.00   1.44 5.4
        1992 12  4   2  8 57.50  34 22.12 -116 53.88   2.97 5.2
        1993  8 21   1 46 38.40  34  1.76 -116 19.27   9.05 5.0
        1994  6 16  16 24 27.52  34 16.07 -116 24.09   3.43 5.0

    The total numbers of quakes in our area are:

        1990    10,738
        1991     9,355
        1992    50,672+
        1993    20,190
        1994    22,217 so far

    The years prior to 1990 had similar numbers to 1990, about 10,000
    per year.  The increase in the past 3 years has been due
    exclusively to the aftershocks of Landers/Big Bear and Northridge.
    The plus sign means that we aren't finished with that part of
    the Landers sequence, and there are likely to have been more quakes
    than the estimate given.
        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 Daylight
    Time listed.

    Table 1
    -------
    Date  Time      N Lat.   W Long.   Mag
    -------------------------------------------------------------
         9/29 12:21 am  36 46.0  118 11.6  2.3  2 mi. S of Independence
         9/29  1:05 am  34 14.4  118 34.7  2.5  2 mi. W of Northridge
         9/29  1:27 am  33 59.6  116 16.3  2.4  13 mi. SE of Yucca Valley
         9/29  5:07 am  34 47.2  116 18.0  2.5  35 mi. SSW of Baker
         9/29  9:30 am  34 47.0  116 18.1  2.0      "
         9/29 12:26 pm  34 21.5  118 39.1  2.1  5 mi. SW of Magic Mtn.
         9/29  2:26 pm  32 57.4  117 39.1  2.0  22 mi. SW of Oceanside
         9/29  8:33 pm  34 34.5  116 37.1  2.0  20 mi. ENE of Lucerne Valley
         9/29 11:44 pm  34 46.5  116 17.5  2.1  36 mi. SSW of Baker
         9/30  2:24 am  34 21.4  116 28.5  2.0  16 mi. N of Yucca Valley
         9/30 10:22 am  34 16.8  118 30.5  2.7  3 mi. NNE of Northridge; FELT
         9/30  5:05 pm  34 48.7  120 58.3  2.2  24 mi. NW of Pt. Arguello
         9/30  6:09 pm  34 46.6  117 13.6  2.1  13 mi. SW of Barstow
         9/30  7:42 pm  35  3.2  116 59.3  2.6  11 mi. N of Barstow
        10/1   9:41 am  34 47.4  116 18.3  2.4  35 mi. SSW of Baker
        10/1  10:15 am  33 14.7  115 37.4  2.0  Obsidian Butte area, 6 mi.
                        W of Niland
        10/1   1:58 pm  34 22.1  118 36.3  2.3  3 mi. SSW of Magic Mtn.
        10/1   5:02 pm  33 59.9  116 34.5  2.0  4 mi. WNW of Desert Hot
                        Springs
        10/1   6:54 pm  34  2.5  117 31.1  2.1  Fontana, 2 mi. SE of the
                        I10/I15 interchange
        10/2   3:56 am  34  9.0  116 25.4  2.1  2 mi. NNE of Yucca Valley
        10/2   8:19 am  34 12.1  116 49.6  2.7  4 mi. SSE of Big Bear City
        10/2   6:09 pm  35  1.4  116 58.5  2.2  9 mi. NNE of Barstow
        10/2   6:19 pm  35  1.3  116 58.5  2.3      "
        10/2   8:25 pm  34 21.1  118 33.5  2.3  2 mi. SW of Newhall
        10/3   1:28 am  34 34.1  120  3.1  3.1  5 mi. ESE of Solvang
        10/3   5:34 am  34 36.8  116 38.5  2.3  20 mi. NE of Lucerne Valley
        10/3  10:14 am  33 41.8  120  6.9  2.1  17 mi. S of Santa Rosa Is.
        10/3   4:50 pm  35 44.7  118  0.6  2.3  20 mi. S of Coso Junction
        10/3   5:25 pm  33 11.7  115 34.1  2.8  Obsidian Butte area, 4 mi.
                        SW of Niland
        10/3  11:06 pm  34 15.7  116 35.5  2.0  12 mi. NW of Yucca Valley
        10/4   3:31 am  33 47.7  117 38.7  2.0  7 mi. SW of Corona
        10/4   7:22 am  34 21.0  118 33.5  2.4  2 mi. SW of Newhall
        10/4  11:29 am  33 54.1  118 33.4  2.2  Offshore, 7 mi. WSW of Los
                        Angeles Airport
        10/4   1:39 pm  34 33.4  116 24.5  2.1  30 mi. N of Yucca Valley
        10/4   2:37 pm  34 30.6  116 31.3  2.0  27 mi. N of Yucca Valley
        10/4   3:54 pm  34 22.2  116 27.3  2.1  17 mi. N of Yucca Valley
        10/4   6:45 pm  34 24.2  116 28.3  2.0  19 mi. N of Yucca Valley
        10/4   7:57 pm  32 55.4  116 20.5  2.2  18 mi. SE of Julian
        10/5   4:16 am  34 19.3  118 32.7  2.1  4 mi. SSW of Newhall
        10/5   5:03 am  35 21.4  118 34.2  2.1  17 mi. NNW of Tehachapi
        10/5  11:22 pm  36 46.0  118 12.0  2.4  2 mi. S of Independence
        -------------------------------------------------------------

        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.

    -------------------------------------------------------------

                                 CDMG ONLINE
                   California Division of Mines and Geology
                        Computer Bulletin Board System


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