| By predicting the intensity of shaking due
to an earthquake before the earthquake occurs we can help plan
to prevent damage. Doing this rapidly after an earthquake can
help manage the emergency response efforts. Intensity is a measure
of the effects of earthquakes. Examples include damage to man-made
structures, ground failure and felt shaking. Intensity is not
the same as magnitude, although it is influenced by earthquake
magnitude.
Intensity is also influenced by distance from the fault,
ground conditions, and, sometimes, directivity. The most commonly
used intensity scale today is the Modified Mercalli Scale.
This is the scale we have used in the predictive models.
These predictive intensity maps have been generated following
the method described in the 1995 ABAG report "On Shaky Ground"
by Jeanne Perkins and John Boatwright. We have generated maps
for the 1868, 1906, and 1989 earthquakes as examples; these
maps show predicted, rather than historical, intensity. New
maps can be generated and posted in minutes after moderate
and large events occur in the Bay Area once the epicenter,
fault strike, and fault length or magnitude have been determined
for the event. These maps are designed to be useful for Emergency
Service Workers, indicating areas likely to have suffered
extensive shaking damage.
Three examples have been generated for historical major earthquakes
in the San Francisco Bay area:
Other
Shaking Hazard Maps
Using this method, maps showing the ground motion expected
for various possible earthquakes in the San Francisco Bay
area have been produced and are available on the WWW from
the Association of Bay Area Governments
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