Off-fault plasticity in three-dimensional dynamic rupture simulations using a modal Discontinuous Galerkin method on unstructured meshes: Implementation, verification and application

Type
Article

Authors
Wollherr, Stephanie
Gabriel, Alice Agnes
Uphoff, Carsten

KAUST Grant Number
ORS-2016-CRG5-3027-04
OSR-CRG2017-3389

Date
2018-05-28

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.

Citation
Wollherr, S., Gabriel, A.-A., & Uphoff, C. (2018). Off-fault plasticity in three-dimensional dynamic rupture simulations using a modal Discontinuous Galerkin method on unstructured meshes: implementation, verification and application. Geophysical Journal International, 214(3), 1556–1584. doi:10.1093/gji/ggy213

Acknowledgements
The work presented in this paper was supported by the German Research Foundation (DFG; project no. KA 2281/4-1, AOBJ 584936/TG-92); by the Bavarian Competence Network for Technical and Scientific High Performance Computing (KONWIHR), project GeoPF (Geophysics for PetaFlop Computing); by the Volkswagen Foundation (project ASCETE - Advanced Simulation of Coupled Earthquake-Tsunami Events, grant no. 88479); by the European Union's Horizon 2020 research and innovation program under grant agreement no. 671698 and by King Abdullah University of Sciene and Technology (KAUST) in Thuwal, Saudi Arabia, under grant ORS-2016-CRG5-3027-04 and OSR-CRG2017-3389. Computing resourceswere provided by the Leibniz Supercomputing Centre (LRZ, projects no. h019z, pr63qo and pr45fi on SuperMUC). The authors thank Dave A. May and Kenneth C. Duru for fruitful discussions. Furthermore, we thank LMU Geophysics' system administrator team for their support (Oeser, 2009). The manuscript benefited from valuable reviews and comments by R. Ando and an anonymous reviewer.

Publisher
Oxford University Press (OUP)

Journal
Geophysical Journal International

DOI
10.1093/GJI/GGY213

Additional Links
https://academic.oup.com/gji/article/214/3/1556/5017447

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