Periodic loading on a creeping fault: Implications for tides

We study the effect of time varying normal and shear stress perturbations on a creeping fault and in which inertia is neglected. When interpreted in terms of earthquake triggering by earth tides, our results suggest that tidal triggering may exist but be very difficult to detect. We use a spring-block model with a rate-and state dependent friction law, loaded at constant velocity, and in which inertia is neglected. When a periodic stress is applied, a resonance exists which can destabilize sliding (i.e. earthquakes). However, when frictional parameters slightly vary along the fault, the observed phase lag between the response of the fault and the perturbating stresses close to resonance shows a broad and uncorrelated scattering.