A Dynamic Earthquake Simulator for Geometrically Complex Faults Governed by Rate- and State- Friction

Dunyu Liu, Benchun Duan, & Bin Luo

Published August 15, 2018, SCEC Contribution #8715, 2018 SCEC Annual Meeting Poster #205

We develop a dynamic earthquake simulator based on finite element methods (FEM) to model dynamics of geometrically complex faults governed by the rate- and state- friction (RSF) over multiple earthquake cycles. The simulator combines a dynamic FEM code EQdyna and a newly developed static FEM code EQquasi to model quasi-static phases of earthquake nucleation, post-seismic and inter-seismic processes. Both FEM codes are parallelized through MPI to speed up computations. EQdyna and EQquasi exchange on-fault physical quantities including shear and normal stresses, slip-rates and state variables. The two-code scheme shows advantages to reconcile the computational challenges from different deformation phases of an earthquake cycle, which are mainly related to 1) handling time steps ranging from hundredths of a second to a few years based on the variable time stepping scheme and 2) the element size small enough to resolve the cohesive zone at the rupture front of dynamic ruptures. The dynamic earthquake simulator is different from most existing earthquake simulators in the community in the sense that it includes fully dynamic rupture propagation and can handle complex fault geometry.

Earthquake cycles on a 3D strike-slip fault with a bend are simulated. The sizes of nucleation patches depend on the normal stress resolved from the regional stress field and stress heterogeneities induced by previous ruptures near the bend. The bend tends to stop dynamic ruptures and accumulates very limited amount of slip over the long-term. Complex earthquake event patterns are identified in the fault system. Earthquakes on the two segments interact. Some earthquakes breaking consecutively the two fault segments can be separated by tens of days, a few days, or even several minutes. The relation between the ratio of the shear stress to the normal stress and the reference friction coefficient in the RSF affects the creeping rate of velocity strengthening regions of the two fault segments. A reduced critical slip distance in the RSF results in faster rupture speed and stronger stress heterogeneity around the bend.

The dynamic earthquake simulator is capable of studying rupture behaviors at the Cajon Pass earthquake gate after further parallelization development of the quasi-static component EQquasi for better scaling.

Key Words
Earthquake cycle simulation, rate- and state- friction, geometrically complex fault

Citation
Liu, D., Duan, B., & Luo, B. (2018, 08). A Dynamic Earthquake Simulator for Geometrically Complex Faults Governed by Rate- and State- Friction. Poster Presentation at 2018 SCEC Annual Meeting.

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