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Spectral-element simulations of long-term fault slip: Effect of low-rigidity layers on earthquake-cycle dynamics

Yoshihiro Kaneko, Jean-Paul Ampuero, & Nadia Lapusta

Published 2011, SCEC Contribution #1477

We develop a spectral element method for the simulation of long-term histories of spontaneous seismic and aseismic slip on faults subjected to slow tectonic loading and governed by rate-and-state friction. Our approach reproduces all stages of earthquake cycles: accelerating slip before dynamic instability, rapid dynamic propagation of earthquake rupture, postseismic slip and interseismic creep. We apply the developed methodology to study the effects of low-rigidity layers on the dynamics of the earthquake cycle in 2-D. We consider two cases: small earthquakes on a planar fault surrounded by a damaged fault zone and large earthquakes on a vertical strike-slip fault that cuts through a shallow low rigidity layer. Our results indicate how the source properties of small repeating earthquakes are affected by the presence of a damaged fault zone: compared to faults in homogeneous media we find (i) reduction in the earthquake nucleation size, (ii) amplification of slip rates during dynamic rupture propagation, (iii) increase in the recurrence interval, and (iv) smaller amount of aseismic slip. Based on a linear stability analysis, we derive a theoretical estimate of the nucleation size as a function of the width and rigidity reduction of the fault zone layer, which is in good agreement with simulated nucleation sizes. We further examine the effects of vertically-stratified bulk layers (e.g., sedimentary basins) on the nature of shallow coseismic slip deficit. For the set of parameters we consider, low-rigidity shallow bulk materials alone do not lead to coseismic slip deficit. While the low-rigidity materials lead to lower interseismic stress accumulation, they also cause dynamic amplification of coseismic slip rates, with the net effect on slip being nearly zero.

Kaneko, Y., Ampuero, J., & Lapusta, N. (2011). Spectral-element simulations of long-term fault slip: Effect of low-rigidity layers on earthquake-cycle dynamics. Journal of Geophysical Research: Solid Earth, 116(B10313). doi: 10.1029/2011JB008395.