17:15 〜 18:45
[SCG40-P41] Episodic Tremor and Slip in a finite-thickness shear zone based on a frictional-viscous model
キーワード：episodic tremor and slip, subduction shear zones
Episodic Tremor and Slip (ETS) represents one type of slow earthquakes, which episodically occurs as a macroscopic slow slip event superposed with local intermittent brittle failures. While some studies have been conducted to investigate ETS, the underlying physical mechanisms are still not well understood. Recently, geological observations have identified a block-in-matrix structure for several exhumed subduction shear zones. This motivates us to investigate the link between subduction shear zones and the spectrum of slow earthquakes, with a particular focus on ETS. Here, we employ a frictional-viscous mélange model, characterized by competent blocks embedded in an incompetent matrix, to numerically simulate fault deformation over a finite-thickness shear zone. The model is based on a visco-elasto-plastic rheology that extends features of classical rate-and-state friction (RSF) to plastic shear bands. By running a large set of numerical simulations, we explore the model parameters that permit ETS-like behaviors. Specifically, we find moderate matrix viscosity and block percentage, velocity-neutral matrix, and velocity-weakening blocks are preferred conditions for producing ETS. Under such conditions, brittle failure mainly occurs in the competent blocks and corresponds to tremor activity, while viscous deformation mainly occurs in the surrounding incompetent matrix and represents slow slip. Furthermore, our model reproduces some key properties of ETS that are consistent with observations, including stress drop (~ kPa) and slip rate (~ 10-3 m/s) for tremor, and slip rate (~ 10-8 m/s) for slow slip. These findings can help constrain the structural and rheological properties of subduction shear zones from ETS source properties, and vice versa.