DEVINE -
Seismic Hazard
Seismic Hazard
Where will the
next major earthquake be?
It is not possible to predict where the next major earthquake will be,
but it is possible to estimate where probable source regions are based
on our geological and geophysical knowledge.
The most important clues are the locations of
How big will it
be?
The size of an earthquake is directly related to the length of fault that
ruptures and the relative displacement between the two sides of the fault.
It is currently impossible to predict what portion of the known, or subsurface
unknown (!), fault will rupture.
A characteristic size may be deduced based on
-
the size of previous ruptures along a well-studied fault,
-
the total strain accumulating in a region from long-term tectonic motion,
and
-
the number and size of earthquakes that have occurred in that zone in the
past.
More importantly, it is important to be able to estimate the probable ground
motion which depends on the
-
distance from the source, and the
-
near surface geologic properties.
When will it occur?
The earthquake process, though unpredictable, follows certain empirical
laws governing the relative distribution of small and large earthquakes.
Constant surveillance of the rate of occurence of small earthquakes allows
extrapolation to the rate of occurence of large earthquakes.
The question that can currently technologically be answered is, What
is the probability that given magnitude earthquake will occur in
a fixed amount of time?
In metropolitan France, there are on the order of 20 earthquakes of
magnitude greater than 3.0 each year (approximately the limit of human
perceptability) and a couple of hundred earthquakes less than 3.0
each year.
Dernier modification 29-Jan-1999
Email: jh@acri.fr
