Temporal clustering of major earthquakes along individual faults due to post-seismic reloading

Abstract

Palaeoseismic evidence suggests that earthquake recurrence intervals in some regions can be highly variable, with clusters of multiple large events separated by much longer periods of quiescence. Because post-seismic processes have a significant effect on the reloading rate of the coseismic fault, we hypothesize that temporal variations in the amount of stress concentrated in the non-seismogenic lithosphere can modulate large earthquake recurrence times. We explore this hypothesis using simple analogue spring-dashpot-slider models. We find that in the presence of small amounts of environmental noise, post-seismic stress transfer over timescales much longer than an earthquake cycle may be an important factor in generating clustering behaviour. The propensity for the system to be clustered is a function of a non-dimensional number that we call the Wallace Number, W. W is defined as the average earthquake stress drop divided by the product of the long-term geologic strain rate across the fault and the effective viscosity of the system. Our results indicate that environments with relatively low strain rates and a relatively weak non-seismogenic lithosphere are most susceptible to clustering driven by post-seismic stress recycling mechanisms.