A physical model of tremor response to external stresses in poroelastic medium

It is known that non-volcanic deep tectonic tremors occur in regions where the pore fluid pressure is higher at depths around 30 km. Because those fluids reduce the effective normal stress on the plate interface significantly, tremors can be triggered by weak perturbing external stresses such as tidal stresses. In particular, during episodic tremor and slip, the following two observational facts have been reported. 1) Sensitivity of tremors to tidal stresses increases dramatically from near zero on the first day of strong activity to the maximum ∼4 days later. 2) The peak tremor occurrence rate corresponds to peak tidal stresses rate on the following day of strong activity and gradually transitions to correspond to peak tidal stresses over subsequent days (Royer et al., 2015).

It is important to construct a model which can explain the above observation results because of estimating the physical state of the fault from the response of tremors to tidal stresses and revealing what the physical processes are essential for understanding such tremor activities. Our model introduces fluid pressure change due to dilatancy to one-degree-of-freedom spring-slider model into aseismic slip region. Using this model, we show that dilatancy is essential to explain the above observation results and that the valid order of magnitude of the characteristic distance Dc of aseismic slip region becomes O(10 ^-3[m]). In addition, we show how tidal sensitivity depends on physical state of fault from a linearized analysis.