Spectrum of slip processes on the subduction interface in relation to long-term deformation in a continuum-based numerical model

Abstract:

In addition to earthquakes, aseismic slip such as slow slip forms a broad spectrum of observed slip processes in terms of duration and size (Peng and Gomberg, NGEO, 2010). It releases a considerable amount of accumlated strain and is thus important when assessing a region's long-term seismic hazard. Here we model the interplay between aseismic slip, seismic slip and aspects of long-term deformation- such as rheology, stress distribution and strength conditions.

For this purpose, we extended our continuum-based numerical model including a visco-elasto-plastic rheology in which cycles of megathrust earthquake-like ruptures were simulated through a purely slip rate-dependent friction, albeit with very low slip rates (van Dinther et al., JGR, 2013). To model a wider slip spectrum and to approach seismic slip rates, we implemented an adaptive time-stepping scheme (Lapusta and Rice, JGR, 2001) and an invariant reformulation of the conventional rate-and state dependent friction (RSF).

We demonstrate that our modelling approach has two main advantages over existing seismic cycle simulations. Firstly, differently oriented faults beyond the megathrust fault can develop spontaneously and become seismically and aseismically activated, while the width of the fault zone depends on the frictional parameters. Secondly, it takes the rheological structure of a subduction zone into account.

In a simplified subduction setup, cycles of spontaneous slip events occur with slip velocities ranging from 10^-9-10^-2 m/s in response to the variation of frictional parameters a, b, and the characteristic slip distance. The transition from stable sliding to seismic events is in general agreement with theoretical estimates of the nucleation size, thereby to first order validating our implementation of RSF. In a more complex rheological setup, we study the interaction between aseismic and seismic slip in relation to the visco-elastic deformation in a layered upper plate consisting of a visco-elasto-plastic crust and a viscous mantle.