Nonlinear Dynamics, Granular Media and Earthquake Triggering
In our work we hypothesize that the dynamic, elastic-nonlinear behaviour of fault gouge perturbed by a seismic wave may be responsible. We base our hypothesis on recent laboratory dynamic experiments conducted in granular media, a fault gouge surrogate. From these we infer that, if the fault is already in a weakened state, seismic waves cause the fault core modulus to abruptly decrease and weaken further. If the fault is already near failure, the process could induce fault slip. Supporting our hypothesis are recent stick-slip laboratory experiments where elastic wave excitation is applied.
Our experiments indicate that elastic waves of strains of order 5x10-5 can cause shear weakening. Recent seismic observations show that a "triggering threshold" exists at strain amplitudes just over 10-6, corresponding to where we observe the onset of elastic nonlinear behavior in the laboratory. Long rang goals include continued testing of the hypothesis with laboratory stick-slip experiments and seismic observations.
Work being conducted in collaboration with Joan Gomberg of the USGS and Chris Marone of the Geosciences Department at the Pennsylvania State University