Rapid 3D dynamic rupture modeling of the February 6, 2023, Kahramanmara\c{s}, Turkey, MWM_W7.8 and MWM_W7.7 earthquake doublet

The 2023 Turkey Earthquake sequence involved unexpected ruptures across numerous fault segments, challenging data interpretation efforts. We present rapid, 3D dynamic rupture simulations to illuminate the complexities of the $M_W$7.8 and $M_W$7.7 earthquake doublet. Constrained by observations available within days of the sequence, our models deliver timely, mechanically consistent explanations for the unforeseen rupture paths, diverse rupture speeds, multiple slip episodes, locally strong shaking, and fault system interactions. We reconcile regional seismo-tectonics, rupture dynamics, and ground motions of a fault system represented by ten curved dipping segments and a heterogeneous stress field. Our simulations link both events matching geodetic and seismic observations. The $M_W$7.8 earthquake features delayed backward branching from a steeply intersecting splay fault, not requiring supershear speeds. The asymmetrical dynamics of the distinct, bilateral $M_W$7.7 event is explained by heterogeneous fault strength, prestress orientation, fracture energy, and static stress changes from the previous event. Our models explain the northward deviation of its western rupture and the minimal slip observed on the S\"urg\"u fault. Rapidly developed 3D dynamic rupture scenarios can elucidate unexpected observations shortly after major earthquakes, providing timely insights for data-driven analysis and hazard assessment toward a comprehensive, physically consistent understanding of the mechanics of multi-fault systems

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

Coupled, Physics-Based Modeling Reveals Earthquake Displacements are Critical to the 2018 Palu, Sulawesi Tsunami

The September 2018, Mw 7.5 Sulawesi earthquake occurring on the Palu-Koro strike-slip fault system was followed by an unexpected localized tsunami. We show that direct earthquake-induced uplift and subsidence could have sourced the observed tsunami within Palu Bay. To this end, we use a physics-based, coupled earthquake–tsunami modeling framework tightly constrained by observations. The model combines rupture dynamics, seismic wave propagation, tsunami propagation and inundation. The earthquake scenario, featuring sustained supershear rupture propagation, matches key observed earthquake characteristics, including the moment magnitude, rupture duration, fault plane solution, teleseismic waveforms and inferred horizontal ground displacements. The remote stress regime reflecting regional transtension applied in the model produces a combination of up to 6 m left-lateral slip and up to 2 m normal slip on the straight fault segment dipping 65∘ East beneath Palu Bay. The time-dependent, 3D seafloor displacements are translated into bathymetry perturbations with a mean vertical offset of 1.5 m across the submarine fault segment. This sources a tsunami with wave amplitudes and periods that match those measured at the Pantoloan wave gauge and inundation that reproduces observations from field surveys. We conclude that a source related to earthquake displacements is probable and that landsliding may not have been the primary source of the tsunami. These results have important implications for submarine strike-slip fault systems worldwide. Physics-based modeling offers rapid response specifically in tectonic settings that are currently underrepresented in operational tsunami hazard assessment

3D Linked Subduction, Dynamic Rupture, Tsunami, and Inundation Modeling: Dynamic Effects of Supershear and Tsunami Earthquakes, Hypocenter Location, and Shallow Fault Slip

Physics-based dynamic rupture models capture the variability of earthquake slip in space and time and can account for the structural complexity inherent to subduction zones. Here we link tsunami generation, propagation, and coastal inundation with 3D earthquake dynamic rupture (DR) models initialized using a 2D seismo-thermo-mechanical geodynamic (SC) model simulating both subduction dynamics and seismic cycles. We analyze a total of 15 subduction-initialized 3D dynamic rupture-tsunami scenarios in which the tsunami source arises from the time-dependent co-seismic seafloor displacements with flat bathymetry and inundation on a linearly sloping beach. We first vary the location of the hypocenter to generate 12 distinct unilateral and bilateral propagating earthquake scenarios. Large-scale fault topography leads to localized up- or downdip propagating supershear rupture depending on hypocentral depth. Albeit dynamic earthquakes differ (rupture speed, peak slip-rate, fault slip, bimaterial effects), the effects of hypocentral depth (25–40 km) on tsunami dynamics are negligible. Lateral hypocenter variations lead to small effects such as delayed wave arrival of up to 100 s and differences in tsunami amplitude of up to 0.4 m at the coast. We next analyse inundation on a coastline with complex topo-bathymetry which increases tsunami wave amplitudes up to ≈1.5 m compared to a linearly sloping beach. Motivated by structural heterogeneity in subduction zones, we analyse a scenario with increased Poisson's ratio of ν = 0.3 which results in close to double the amount of shallow fault slip, ≈1.5 m higher vertical seafloor displacement, and a difference of up to ≈1.5 m in coastal tsunami amplitudes. Lastly, we model a dynamic rupture “tsunami earthquake” with low rupture velocity and low peak slip rates but twice as high tsunami potential energy. We triple fracture energy which again doubles the amount of shallow fault slip, but also causes a 2 m higher vertical seafloor uplift and the highest coastal tsunami amplitude (≈7.5 m) and inundation area compared to all other scenarios. Our mechanically consistent analysis for a generic megathrust setting can provide building blocks toward using physics-based dynamic rupture modeling in Probabilistic Tsunami Hazard Analysis

Flexible Modellerweiterung und Optimierung von Erdbebensimulationen

Simulations of realistic earthquake scenarios require scalable software and extensive supercomputing resources. With increasing fidelity in simulations, advanced rheological and source models need to be incorporated. I introduce a domain-specific language in order to handle the model flexibility in combination with the high efficiency requirements. The contributions in this thesis enabled the to date largest and longest dynamic rupture simulation of the 2004 Sumatra earthquake.Realistische Erdbebensimulationen benötigen skalierbare Software und beträchtliche Rechenressourcen. Mit zunehmender Genauigkeit der Simulationen müssen fortschrittliche rheologische und Quellmodelle integriert werden. Ich führe eine domänenspezifische Sprache ein, um die Modelflexibilität in Kombination mit den hohen Effizienzanforderungen zu beherrschen. Die Beiträge in dieser Arbeit haben die bisher größte und längste dynamische Bruchsimulation des Sumatra-Erdbebens von 2004 ermöglicht

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

Linked 3-D modelling of megathrust earthquake-tsunami events: from subduction to tsunami run up

How does megathrust earthquake rupture govern tsunami behaviour? Recent modelling advances permit evaluation of the influence of 3-D earthquake dynamics on tsunami genesis, propagation, and coastal inundation. Here, we present and explore a virtual laboratory in which the tsunami source arises from 3-D coseismic seafloor displacements generated by a dynamic earthquake rupture model. This is achieved by linking open-source earthquake and tsunami computational models that follow discontinuous Galerkin schemes and are facilitated by highly optimized parallel algorithms and software. We present three scenarios demonstrating the flexibility and capabilities of linked modelling. In the first two scenarios, we use a dynamic earthquake source including time-dependent spontaneous failure along a 3-D planar fault surrounded by homogeneous rock and depth-dependent, near-lithostatic stresses. We investigate how slip to the trench influences tsunami behaviour by simulating one blind and one surface-breaching rupture. The blind rupture scenario exhibits distinct earthquake characteristics (lower slip, shorter rupture duration, lower stress drop, lower rupture speed), but the tsunami is similar to that from the surface-breaching rupture in run-up and length of impacted coastline. The higher tsunami-generating efficiency of the blind rupture may explain how there are differences in earthquake characteristics between the scenarios, but similarities in tsunami inundation patterns. However, the lower seafloor displacements in the blind rupture result in a smaller displaced volume of water leading to a narrower inundation corridor inland from the coast and a 15 per cent smaller inundation area overall. In the third scenario, the 3-D earthquake model is initialized using a seismo-thermo-mechanical geodynamic model simulating both subduction dynamics and seismic cycles. This ensures that the curved fault geometry, heterogeneous stresses and strength and material structure are consistent with each other and with millions of years of modelled deformation in the subduction channel. These conditions lead to a realistic rupture in terms of velocity and stress drop that is blind, but efficiently generates a tsunami. In all scenarios, comparison with the tsunamis sourced by the time-dependent seafloor displacements, using only the time-independent displacements alters tsunami temporal behaviour, resulting in later tsunami arrival at the coast, but faster coastal inundation. In the scenarios with the surface-breaching and subduction-initialized earthquakes, using the time-independent displacements also overpredicts run-up. In the future, the here presented scenarios may be useful for comparison of alternative dynamic earthquake-tsunami modelling approaches or linking choices, and can be readily developed into more complex applications to study how earthquake source dynamics influence tsunami genesis, propagation and inundation

Numerical simulations of seismo-acoustic nuisance patterns from an induced M1.8 earthquake in the Helsinki, southern Finland, metropolitan area

Irritating earthquake sounds, reported also at low ground shaking levels, can negatively impact the social acceptance of geo-engineering applications. Concurringly, earthquake sound patterns have been linked to faulting mechanisms, thus opening possibilities for earthquake source characterisation. Inspired by consistent reports of felt and heard disturbances associated with the weeks-long stimulation of a 6 km-deep geothermal system in 2018 below the Otaniemi district of Espoo, Helsinki, we conduct fully-coupled 3D numerical simulations of wave propagation in solid Earth and the atmosphere. We assess the sensitivity of ground shaking and audible noise distributions to the source geometry of small induced earthquakes, using the largest recorded event in 2018 of magnitude ML=1.8. Utilizing recent computational advances, we are able to model seismo-acoustic frequencies up to 25 Hz therefore reaching the lower limit of human sound sensitivity. Our results provide for the first time synthetic spatial nuisance distributions of audible sounds at the 50-100 m scale for a densely populated metropolitan region. In five here presented 3D coupled elastic-acoustic scenario simulations, we include the effects of topography and subsurface structure, and analyse the audible loudness of earthquake generated acoustic waves. We can show that in our region of interest, S-waves are generating the loudest sound disturbance. We compare our sound nuisance distributions to commonly used empirical relationships using statistical analysis. We find that our 3D synthetics are generally smaller than predicted empirically, and that the interplay of source-mechanism specific radiation pattern and topography can add considerable non-linear contributions. Our study highlights the complexity and information content of spatially variable audible effects, even when caused by very small earthquakes.Comment: 29 pages, 9 figures. This paper has been submitted to the Bulletin of the Seismological Society of America for publicatio