Abstract
The dynamics and potential size of earthquakes depend crucially on rupture transfers between adjacent fault segments. To accurately describe earthquake source dynamics, numerical models can account for realistic fault geometries and rheologies such as nonlinear inelastic processes off the slip interface. We present implementation, verification and application of off-fault Drucker–Prager plasticity in the open source software SeisSol (www.seissol.org). SeisSol is based on an arbitrary high-order derivative modal Discontinuous Galerkin method using unstructured, tetrahedral meshes specifically suited for complex geometries. Two implementation approaches are detailed, modelling plastic failure either employing subelemental quadrature points or switching to nodal basis coefficients. At fine fault discretizations, the nodal basis approach is up to six times more efficient in terms of computational costs while yielding comparable accuracy. Both methods are verified in community benchmark problems and by 3-D numerical h- and p-refinement studies with heterogeneous initial stresses. We observe no spectral convergence for on-fault quantities with respect to a given reference solution, but rather discuss a limitation to low-order convergence for heterogeneous 3-D dynamic rupture problems. For simulations including plasticity, a high fault resolution may be less crucial than commonly assumed, due to the regularization of peak slip rate and an increase of the minimum cohesive zone width. In large-scale dynamic rupture simulations based on the 1992 Landers earthquake, we observe high rupture complexity including reverse slip, direct branching and dynamic triggering. The spatiotemporal distribution of rupture transfers are altered distinctively by plastic energy absorption, correlated with locations of geometrical fault complexity. Computational cost increases by 7 per cent when accounting for off-fault plasticity in the demonstrating application. Our results imply that the combination of fully 3-D dynamic modelling, complex fault geometries and off-fault plastic yielding is important to realistically capture dynamic rupture transfers in natural fault systems.
Highlights
Understanding the physics of earthquake source processes enhances seismic hazard assessment for natural fault systems
Directivity effects as well as potential rupture transfers to adjacent fault segments are determined by earthquake source dynamics
Comparing on-fault slip rates (Fig. 3a), we observe that plastic yielding significantly reduces peak slip rate and delays rupture arrival time as confirmed in various dynamic rupture models accounting for plastic energy dissipation (i.e. Andrews 2005; Dunham et al 2011a; Gabriel et al 2013; Roten et al 2015)
Summary
Understanding the physics of earthquake source processes enhances seismic hazard assessment for natural fault systems. Directivity effects as well as potential rupture transfers to adjacent fault segments are determined by earthquake source dynamics. Numerical simulations pose a powerful tool to further our understanding of earthquake rupturing (complex) faults. In modelling earthquake rupture dynamics, the fault geometry in conjunction with fault stress and strength constitute essential initial conditions, determining frictional failure, rupture propagation and seismic wave emanation off the fault. Such models can describe the interaction of fault slip with the surrounding host-rock material, for example, by considering off-fault plastic deformation. Smallest element edge length Polynomial degree (space and time) Plastic cohesion Bulk friction
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