Abstract
Source parameters for historical earthquakes worldwide are compiled
to develop a series of empirical relationships among moment magnitude
(M), surface rupture length, subsurface rupture length, downdip rupture
width, rupture area, and maximum and average displacement per event.
The resulting data base is a significant update of previous compilations
and includes the additional source parameters of seismic moment,
moment magnitude, subsurface rupture length, downdip rupture width,
and average surface displacement. Each source parameter is classified
as reliable or unreliable, based on our evaluation of the accuracy
of individual values. Only the reliable source parameters are used
in the final analyses. In comparing source parameters, we note the
following trends: (1) Generally, the length of rupture at the surface
is equal to 75\% of the subsurface rupture length; however, the ratio
of surface rupture length to subsurface rupture length increases
with magnitude; (2) the average surface displacement per event is
about one-half the maximum surface displacement per event; and (3)
the average subsurface displacement on the fault plane is less than
the maximum surface displacement but more than the average surface
displacement. Thus, for most earthquakes in this data base, slip
on the fault plane at seismogenic depths is manifested by similar
displacements at the surface. Log-linear regressions between earthquake
magnitude and surface rupture length, subsurface rupture length,
and rupture area are especially well correlated, showing standard
deviations of 0.25 to 0.35 magnitude units. Most relationships are
not statistically different (at a 95\% significance level) as a function
of the style of faulting: thus, we consider the regressions for all
slip types to be appropriate for most applications. Regressions between
magnitude and displacement, magnitude and rupture width, and between
displacement and rupture length are less well correlated and have
larger standard deviation than regressions between magnitude and
length or area. The large number of data points in most of these
regressions and their statistical stability suggest that they are
unlikely to change significantly in response to additional data.
Separating the data according to extensional and compressional tectonic
environments neither provides statistically different results nor
improves the statistical significance of the regressions. Regressions
for cases in which earthquake magnitude is either the independent
or the dependent parameter can be used to estimate maximum earthquake
magnitudes both for surface faults and for subsurface seismic sources
such as blind faults, and to estimate the expected surface displacement
along a fault for a given size earthquake.
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