Inelastic material response in multi-physics earthquake rupture simulations

Dynamic rupture models are able to shed light on earthquake source dynamics where direct observations are rare or non-existent. These multi-physics simulations incorporate earthquake rupture along a fault governed by frictional constitutive laws, which is coupled to seismic wave propagation described by the linear elastic wave equation. To accurately model the earthquake process, numerical models need to include realistic material properties such as the ability of rocks to deform plastically. This dissertation extends the Arbitrary High Order Derivative Discontinuous Galerkin (ADER-DG) framework of the dynamic rupture software SeisSol to account for non-linear off-fault plasticity. The impact of plasticity on rupture dynamics and the emitted seismic wave field is investigated in realistic simulations motivated by past earthquakes on geometrically complex faults. We first present the implementation of off-fault plasticity, which is verified in community benchmark problems and by three-dimensional numerical refinement studies. Motivated by the high efficiency of the implementation, we present a large-scale simulation of earthquake rupture along the segmented fault system of the 1992 Landers earthquake including plasticity. The results indicate that spatio-temporal rupture transfers are altered by plastic energy absorption, correlating with locations of geometrical fault complexity. In a next step, the model of the 1992 Landers earthquake is further extended to account for a new degree of realism among dynamic rupture models by incorporating high-resolution topography, 3D velocity structure, and viscoelastic attenuation in addition to off-fault plasticity. The simulation reproduces a broad range of observations including moment release rate, seismic waveform characteristics, mapped off-fault deformation patterns, and peak ground motions. We find that plasticity reduces the directivity effect and the spatial variability of peak ground velocities in comparison to the purely elastic simulation. In addition to this continental strike-slip earthquake, we investigate the effect of off-fault plasticity on source dynamics and seafloor deformation in a 3D subduction zone model of the 2004 Sumatra-Andaman earthquake. Simulated seafloor displacements are drastically altered by inelastic processes within the entire accretionary wedge, depending on fault- strike and the applied regional stress field, which potentially affects the tsunamigenesis. Finally, since these application scenarios show that rupture dynamics and the occurrence of off-fault plasticity are highly influenced by the assumed initial stresses and fault geometry, we propose a workflow to constrain dynamic rupture initial conditions with plasticity by long-term seismic cycling modelling. The exploited seismo-thermo-mechanical model provides a self-consistent slab geometry as well as initial stress and strength conditions that evolve according to the tectonic stress build-up and the temperature-dependent strength of the rocks. The geomechanically constrained subduction zone model suggests that the accretionary wedge is very close to plastic failure such that the occurrence of plastic strain hampers rupture to the trench, but locally increases the vertical seafloor uplift

Inelastic material response in multi-physics earthquake rupture simulations

Dynamic rupture models are able to shed light on earthquake source dynamics where direct observations are rare or non-existent. These multi-physics simulations incorporate earthquake rupture along a fault governed by frictional constitutive laws, which is coupled to seismic wave propagation described by the linear elastic wave equation. To accurately model the earthquake process, numerical models need to include realistic material properties such as the ability of rocks to deform plastically. This dissertation extends the Arbitrary High Order Derivative Discontinuous Galerkin (ADER-DG) framework of the dynamic rupture software SeisSol to account for non-linear off-fault plasticity. The impact of plasticity on rupture dynamics and the emitted seismic wave field is investigated in realistic simulations motivated by past earthquakes on geometrically complex faults. We first present the implementation of off-fault plasticity, which is verified in community benchmark problems and by three-dimensional numerical refinement studies. Motivated by the high efficiency of the implementation, we present a large-scale simulation of earthquake rupture along the segmented fault system of the 1992 Landers earthquake including plasticity. The results indicate that spatio-temporal rupture transfers are altered by plastic energy absorption, correlating with locations of geometrical fault complexity. In a next step, the model of the 1992 Landers earthquake is further extended to account for a new degree of realism among dynamic rupture models by incorporating high-resolution topography, 3D velocity structure, and viscoelastic attenuation in addition to off-fault plasticity. The simulation reproduces a broad range of observations including moment release rate, seismic waveform characteristics, mapped off-fault deformation patterns, and peak ground motions. We find that plasticity reduces the directivity effect and the spatial variability of peak ground velocities in comparison to the purely elastic simulation. In addition to this continental strike-slip earthquake, we investigate the effect of off-fault plasticity on source dynamics and seafloor deformation in a 3D subduction zone model of the 2004 Sumatra-Andaman earthquake. Simulated seafloor displacements are drastically altered by inelastic processes within the entire accretionary wedge, depending on fault- strike and the applied regional stress field, which potentially affects the tsunamigenesis. Finally, since these application scenarios show that rupture dynamics and the occurrence of off-fault plasticity are highly influenced by the assumed initial stresses and fault geometry, we propose a workflow to constrain dynamic rupture initial conditions with plasticity by long-term seismic cycling modelling. The exploited seismo-thermo-mechanical model provides a self-consistent slab geometry as well as initial stress and strength conditions that evolve according to the tectonic stress build-up and the temperature-dependent strength of the rocks. The geomechanically constrained subduction zone model suggests that the accretionary wedge is very close to plastic failure such that the occurrence of plastic strain hampers rupture to the trench, but locally increases the vertical seafloor uplift

Landers 1992 ”reloaded”: Integrative dynamic earthquake rupture modeling

The 1992 $M_w$ 7.3 Landers earthquake is perhaps one of the best studied seismic events. However, many aspects of the dynamics of the rupture process are still puzzling, e.g. how did rupture transfer between fault segments? We present 3D spontaneous dynamic rupture simulations of a new degree of realism, incorporating the interplay of fault geometry, topography, 3D rheology, off-fault plasticity and viscoelastic attenuation. The surprisingly unique scenario reproduce a broad range of observations, including final slip distribution, seismic moment-rate function, seismic waveform characteristics and peak ground velocities, as well as shallow slip deficits and mapped off-fault deformation patterns. Sustained dynamic rupture of all fault segments in general, and rupture transfers in particular, put strong constraints on amplitude and orientation of initial fault stresses and friction. Source dynamics include dynamic triggering over large distances and direct branching; rupture terminates spontaneously on most of the principal fault segments. We achieve good agreement between synthetic and observed waveform characteristics and associated peak ground velocities. Despite very complex rupture evolution, ground motion variability is close to what is commonly assumed in Ground Motion Prediction Equations. We examine the effects of variations in modeling parameterization, e.g. purely elastic setups or models neglecting viscoelastic attenuation, in comparison to our preferred model. Our integrative dynamic modeling approach demonstrates the potential of consistent in-scale earthquake rupture simulations for augmenting earthquake source observations and improving the understanding of earthquake source physics of complex, segmented fault systems

Setup of the 2004 Sumatra-Andaman earthquake for SeisSol, version Shaking Corals

Sample input dataset of the 2004 Sumatra-Andaman earthquake for SeisSol, version Shaking corals. The mesh consists of 3.645.163 elements and is partitioned to run with 20 MPI processes. SeisSol can be obtained from from Github (https://github.com/SeisSol/SeisSol/releases/tag/201703). A description on how to set up SeisSol is available in the artifact description of Uphoff et al. "Extreme scale multi-physics simulations of the tsunamigenic 2004 Sumatra megathrust earthquake", 2017 and in the Github Wiki (https://github.com/SeisSol/SeisSol/wiki)

Setup of the TPV16 benchmark for dynamic rupture verification

Verification benchmark for simulations with dynamic rupture and local time stepping with SeisSol, version Shaking Corals. More details can be found in the publication Uphoff et al. "Extreme scale multi-physics simulations of the tsunamigenic 2004 Sumatra megathrust earthquake", 2017 and on the project homepage (http://www.seissol.org/)

A Suite of Exercises for Verifying Dynamic Earthquake Rupture Codes

The article of record as published may be found at http://dx.doi.org/10.1785/0220170222We describe a set of benchmark exercises that are designed to test if computer codes that simulate dynamic earthquake rupture are working as intended. These types of computer codes are often used to understand how earthquakes operate, and they produce simulation results that include earthquake size, amounts of fault slip, and the patterns of ground shaking and crustal deformation. The benchmark exercises examine a range of features that scientists incorporate in their dynamic earthquake rupture simulations. These include implementations of simple or complex fault geometry, off-fault rock response to an earthquake, stress conditions, and a variety of formulations for fault friction. Many of the benchmarks were designed to investigate scientific problems at the forefronts of earthquake physics and strong ground motions research. The exercises are freely available on our website for use by the scientific community.Southern California Earthquake Center (SCEC