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

Abstract

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.

Earthquake Rupture on Multiple Splay Faults and Its Effect on Tsunamis

“…Slip on the megathrust propagating onto splays through dynamic or static stress changes has been inferred for past and recent tsunamigenic earthquakes (e.g., Cummins & Kaneda, 2000; Fan et al., 2017; Obana et al., 2017). Our results highlight that studying compound rupture of megathrusts and multiple or segmented splay faults is important for the assessment of future hazardous events and to better understand the details of near‐trench rupture processes that control seafloor uplift and hence tsunami generation (Madden et al., 2020; Saito et al., 2019; Satake, 2015; Tanioka & Satake, 1996; Ulrich et al., 2022; Wirp et al., 2021). Future efforts could aim to include region‐specific observations, such as high‐resolution seismic imaging and geological data in modeling workflows that link earthquake source models to tsunami models to improve our understanding of tsunamigenesis.…”

“…To relate our findings directly to tsunami data, the here found splay fault effects should be analyzed with more complex bathymetry and 3‐D complexity in future studies (Bletery et al., 2015; Matsuyama et al., 1999; Tonini et al., 2020; Ulrich et al., 2019). Recent studies using a similar methodology to the one presented here have already attempted this for megathrust‐only events (Madden et al., 2020; Wirp et al., 2021). However, one of the major limitations in these 3‐D studies is the uncertainties in how to accurately account for any lateral variation in the initial stresses and strengths on the megathrust since the considered geodynamic seismic cycle model is two‐dimensional.…”

“…(2020) and Wirp et al. (2021) for a subduction zone setting, where the stresses and strengths are adapted to avoid unilateral nucleation along the 2D fault and thereby reduce fault slip. The 3D megathrust dynamic rupture models in Wirp et al.…”

The state of pore fluid pressure and 3D megathrust earthquake dynamics

“…SeisSol solves the seismic wave equation in velocitystress formulation using an Arbitrary high-order DERivate Discontinuous Galerkin (ADER-DG) scheme (Dumbser & Käser, 2006). Computational optimizations target supercomputers with many-core CPUs (Breuer et al, 2014;Heinecke et al, 2014;Rettenberger et al, 2016;Krenz et al, 2021). SeisSol uses local time stepping, which increases runtime efficiency by decreasing dependence of the time-step on the element with the small- Yellow surface is the megathrust, which intersects the seafloor to left and reaches 50 km depth to right.…”

“…Others initialize dynamic rupture models with conditions, including initial P f , from geodynamic and seismic cycling modeling that captures long term subduction zone deformation and fluid flow (I. Zelst et al, 2019;Wirp et al, 2021;Madden et al, 2021). Rice (1992) shows that fluid at elevated pressures within a fault zone may follow the same gradient with depth as the lithostatic stress, causing constant effective normal stress with depth.…”