Off-fault plasticity in dynamic rupture simulations: 3D numerical analysis and effects on rupture transfer in complex fault geometries

Stephanie Wollherr, & Alice-Agnes Gabriel

Published August 15, 2016, SCEC Contribution #6733, 2016 SCEC Annual Meeting Poster #062

Estimating the potential dimension of a future earthquake hosted by a complex fault system depends crucially on rupture branching and jumping dynamics between adjacent fault segments. Numerical modelling of such earthquake source dynamics requires realistic physical assumptions, such as the incorporation of plastic yielding around the fault induced by high stresses at the rupture tip. Further, high-resolution numerical methods are needed for a precisely capturing of on- and off-fault dynamics in conjunction with seismic wave propagation.

Here we present three-dimensional dynamic rupture simulations with off-fault plasticity focusing on numerical convergence and the influence on rupture transfers between fault segments in an application scenario. The simulations are performed with SeisSol (www.seissol.org), an open-source software package based on the high-order ADER-DG method solving frictional sliding coupled to seismic wave propagation. We first verify the (visco-) plastic implementation by benchmark tests of the SCEC Spontaneous Rupture Code-Validation project. To demonstrate the consistency of this nonlinear rheology in a 3D modal DG approach we perform in-depth on-fault convergence tests. Our results show that plasticity regularizes a mesh-dependency of peak slip rate observed in purely elastic simulations. On the other hand, plasticity reduces the required mesh discretization for a consistent rupture arrival time compared to elastic simulations.

The ADER-DG method is especially suited for complex geometries by allowing the usage of unstructured tetrahedral meshes. In this context, we investigate how plastic yielding influences the rupture propagation in a large-scale dynamic rupture scenario based on the 1992 Landers earthquake. Our numerical model reproduces well the total rupture duration and the seismic moment of the event. We observe complex rupture evolution including branching, dynamically triggered slip and back-propagation on different fault segments. Due to plastic yielding between branching segments, part of the seismic energy is absorbed by plastic processes, which affects in turn the on-fault source dynamics. In comparison to an elastic scenario, off-fault plasticity clearly reduces the peak slip rate on the whole fault up to 30 %. The elastic and plastic scenarios exhibit distinct spatio-temporal rupture transfers between fault segments, which also alters the final slip distribution. Our results indicate that off-fault plasticity plays an important role when assessing potential seismic risks on complex fault geometries where parts of the fault might be triggered dynamically.

Key Words
off-fault plasticity, , inelastic deformation, dynamic rupture simulation, source dynamics, rupture jumps, rupture branching

Citation
Wollherr, S., & Gabriel, A. (2016, 08). Off-fault plasticity in dynamic rupture simulations: 3D numerical analysis and effects on rupture transfer in complex fault geometries. Poster Presentation at 2016 SCEC Annual Meeting.

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