Modeling sequences of seismic and aseismic deformation in a nonlinear viscoelastic megathrust

Luca Dal Zilio, Nadia Lapusta, Jean-Philippe Avouac, & Taras Gerya

Published August 16, 2021, SCEC Contribution #11484, 2021 SCEC Annual Meeting Poster #152

A major goal in earthquake physics is to develop a constitutive framework for fault slip that captures the dependence of shear strength on sliding velocity, nonlinear rheology, and temperature. In this study, we present VELO2CYCLEs (Visco-ELastO 2-D Cycles of Earthquakes), a two-dimensional (2-D) thermo-mechanical computational framework for simulating earthquake sequences in a nonlinear viscoelastic compressible media. The method is developed for a plane-strain problem and incorporates an invariant formulation of the classical rate- and state-dependent friction equations and an adaptive time-stepping that allows the time step to vary by many orders of magnitude during a simulation. Long-term tectonic convergence is imposed by displacing a boundary at a constant rate, whereas temperature-dependent viscosity is incorporated via a rapidly-converging Newton-Raphson scheme. The 2-D volume is discretized using finite differences with a fully staggered grid and marker-in-cell techniques. An adaptive free-surface approximation is used to modulate the air viscosity with the time step, which allows stresses to vanish on the free surface during the propagation of fast slipping events. To demonstrate the versatility of the methodology, we tackle a set of increasingly complex models in which we investigate how inertial wave-mediated effects, radiation damping, thermally activated nonlinear rheology, and off-megathrust splay-fault events affect sequences of seismic and aseismic slip on a simplified subduction megathrust. The relatively simple model setup allows us to compare the modeling results against other computational methods in the literature and simple analytical solutions in the context of observations of large megathrust earthquakes. The new method provides a unique computational framework to analyze earthquake sequences and connect forearc deformation with the dynamic properties of the megathrust, thus providing a physical link between observations of individual earthquakes and postseismic deformation with geological observations of long-term tectonic deformation.

Key Words
Earthquake sequences, Subduction Megathrust, Visco-Elasto Rheology, Rate-and-State Friction, Finite Difference

Citation
Dal Zilio, L., Lapusta, N., Avouac, J., & Gerya, T. (2021, 08). Modeling sequences of seismic and aseismic deformation in a nonlinear viscoelastic megathrust. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)