Fault trace complexity, cumulative slip, and the shape of the magnitude-frequency
distribution for strike-slip faults: a global survey
Geophysical Journal International, 124 (3):
833--868 (March 1996)DOI: 10.1111/j.1365-246X.1996.tb05641.x
Abstract
We examine whether the shape of the magnitude-frequency distribution
for strike-slip faults is described by the Gutenburg-Richter relationship
(log n=a - bM) or by the characteristic earthquake model, by analysing
a data set of faults from California. Mexico, Japan, New Zealand,
China and Turkey. For faults within regional seismic networks, curves
of the form log n yr-1=a-bM, where n yr-1 is the number of events
per year equal to magnitude M, are fit to the instrumental record
of seismicity and geological data are used to estimate independently
the size and recurrence rate of the largest expected earthquakes
that would rupture the total length of the fault. Extrapolation of
instrumentally derived curves to larger magnitudes agrees with geological
estimates of the recurrence rate of the largest earthquakes for only
four of the 22 faults if uncertainties in curve slope are considered,
and significantly underestimates the geological recurrence rates
in the remaining cases. Also, if we predict the seismicity of the
faults as a function of fault length and slip rate, and the predicted
seismicity is distributed in accord with the Gutenburg-Richter relationship,
we find the predicted recurrence rate to be greater than the observed
recurrence rates of smaller earthquakes along most faults. If individual
fault zones satisfy the Gutenburg-Richter relationship over the long
term, our observations imply that, during the recurrence interval
of the largest expected earthquakes, the recurrence of lesser-sized
events is not steady but, rather, strongly clustered in time. However,
if the instrumental records provide an estimate of the long-term
rate of small to moderate earthquakes along the faults, our observations
imply that the faults generally exhibit a magnitude-frequency distribution
consistent with the characteristic earthquake model. Aiso, we observe
that the geometrical complexity of strike-slip faults is a decreasing
function of cumulative strike-slip offset. The four faults we observe
to be consistent with the Gutenburg-Richter relationship are among
those characterized by the least amount of cumulative slip and greatest
fault-trace complexity. We therefore suggest that the ratio of the
recurrence rate of small to large earthquakes along a fault zone
may decrease as slip accumulates and the fault becomes smoother.