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A mechanism for preseismic steady rupture fronts observed in laboratory experiments

Yoshihiro Kaneko, & Jean-Paul Ampuero

Published 2011, SCEC Contribution #1511

It has been shown that the onset of frictional instability is characterized by a transition from stable, quasi-static rupture growth to unstable, inertially-controlled high-speed rupture. In particular, slow rupture fronts propagating at a steady speed Vslow of the order of 5 percent of the S-wave speed have been observed prior to the onset of dynamic rupture in recent fault-friction laboratory experiments. However, the precise mechanism governing this Vslow stage is unknown. Here we reproduce this phenomenon in numerical simulations of earthquake sequences that incorporate laboratory-derived rate-and-state friction laws. Our simulations show that the Vslow stage originates from a stress concentration inherited from the coalescence of interseismic slow creep fronts. Its occurrence is limited to a narrow range of the parameter space but is found in simulations with two commonly-used state-variable evolution laws in the rate-and-state formulation. The sensitivity of the speed Vslow to the model parameters suggests that the propagation speed Vslow reported in laboratory experiments may also be sensitive to parameters of friction and stress conditions. Our results imply that time and space dimensions associated with the propagation of Vslow on natural faults can be as much as a few seconds and several hundred meters, respectively. Hence the detection of such preseismic signals may be possible with near-field high-resolution observations.

Key Words
slip instability, rock friction, earthquake, nucleation, faults, onset, laws

Kaneko, Y., & Ampuero, J. (2011). A mechanism for preseismic steady rupture fronts observed in laboratory experiments. Geophysical Research Letters, 38(L21307). doi: 10.1029/2011GL049953.