SCSN (TriNet) Aftershock Forecast
                         == AFTERSHOCK FORECAST ==

 Southern California Seismic Network (TriNet) operated by Caltech and USGS

 Version 1: This report supersedes any earlier forecasts about this event.

 Magnitude   :   5.1  Ml
 Time        :   30 Oct 2001   11:56:16 PM PST
             :   31 Oct 2001   07:56:16 UTC
 Coordinates :   33 deg. 30.18 min. N,  116 deg. 31.20 min. W
 Event ID    :   9718013

 STRONG AFTERSHOCKS (Magnitude 5 and larger) -
 At this time (immediately after the mainshock) the probability of a
 strong and possibly damaging aftershock IN THE NEXT 7 DAYS is
 less than 10 PERCENT.

 Most likely, the recent mainshock will be the largest in the sequence.
 However, there is a small chance (APPROXIMATELY 5 TO 10 PERCENT) of an 
 earthquake equal to or larger than this mainshock in the next 7 days.

 WEAK AFTERSHOCKS (Magnitude 3 to 5) -
 In addition, approximately 2 to 12 SMALL AFTERSHOCKS are expected in
 the same 7-DAY PERIOD and may be felt locally.

 This forecast is based on the statistics of aftershocks typical for
 California.  This is not an exact prediction, but only a rough guide to
 expected aftershock activity. This forecast may be revised as more
 information becomes available.

                  Background Information About Aftershocks

 Like most earthquakes, the recent earthquake is expected to be followed
 by numerous aftershocks.  Aftershocks are additional earthquakes that
 occur after the mainshock and in the same geographic area.  Usually,
 aftershocks are smaller than the mainshock, but occasionally an
 aftershock may be strong enough to be felt widely throughout the area
 and may cause additional damage, particularly to structures already
 weakened in the mainshock.  As a rule of thumb, aftershocks of
 magnitude 5 and larger are considered potentially damaging.

 Aftershocks are most common immediately after the mainshock; their
 average number per day decreases rapidly as time passes.  Aftershocks
 are most likely to be felt in the first few days after the mainshock, but may be
 felt weeks, months, or even years afterwards.  In general,
 the larger the mainshock, the longer its aftershocks will be felt.

 Aftershocks tend to occur near the mainshock, but the exact geographic
 pattern of the aftershocks varies from earthquake to earthquake and is
 not predictable.  The larger the mainshock, the larger the area of
 aftershocks.  While there is no "hard" cutoff distance beyond which an
 earthquake is totally incapable of triggering an aftershock, the vast
 majority of aftershocks are located close to the mainshock.  As a rule
 of thumb, a magnitude 6 mainshock may have aftershocks up to 10 to 20
 miles away, while a magnitude 7 mainshock may have aftershocks as far
 as 30 to 50 miles away.

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