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

Abstract

Summary How does megathrust earthquake rupture govern tsunami behavior? Recent modeling advances permit evaluation of the influence of 3D earthquake dynamics on tsunami genesis, propagation, and coastal inundation. Here, we present and explore a virtual laboratory in which the tsunami source arises from 3D 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 modeling. In the first two scenarios, we use a dynamic earthquake source including time-dependent spontaneous failure along a 3D planar fault surrounded by homogeneous rock and depth-dependent, near-lithostatic stresses. We investigate how slip to the trench influences tsunami behavior 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 % smaller inundation area overall. In the third scenario, the 3D 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 modeled 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 behavior, 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 over-predicts run-up. In the future, the here presented scenarios may be useful for comparison of alternative dynamic earthquake-tsunami modeling 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.

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

“…Here, we summarize the computational methods used for simulating subduction-initialized dynamic earthquake rupture linked to tsunami generation, propagation, and inundation (Figure 1). For an in-depth description of the virtual laboratory for modeling tsunami sources arising from 3D co-seismic seafloor displacements generated by dynamic earthquake rupture models, we refer to Madden et al (2020). We compute 3D dynamic earthquake rupture and seismic wave propagation with SeisSol (https:/seissol.org).…”

“…Dynamic rupture earthquake models can yield stochastic slip distributions, too, under the assumption of stochastic loading stresses (Geist and Oglesby, 2014). Such physics-based models can be directly linked to tsunami models by using the time-independent or timedependent seafloor displacements (and potentially velocities) as the tsunami source (Kozdon and Dunham, 2013;Ryan et al, 2015;Lotto et al, 2017b;Saito et al, 2019;Madden et al, 2020). For instance, time-dependent 3D displacements from observational constrained dynamic rupture scenarios of the 2018 Palu, Sulawesi earthquake and the 2004 Sumatra-Andaman earthquake are linked to a hydrostatic shallow water tsunami model by Ulrich et al (2019b).…”

“…Particularly in subduction zones where observational data are sparse, space and time scales vary over many orders of magnitude and both geometric and rheological megathrust complexities are likely to control rupture characteristics. Recently, initial conditions for 2D and 3D megathrust dynamic rupture earthquake models have been informed from 2D geodynamic long-term subduction and seismic cycle models (van Zelst et al, 2019;Madden et al, 2020;van Zelst et al, 2021). This approach provides self-consistent initial fault loading stresses and frictional strength, fault geometry and material properties on and surrounding the megathrust, as well as consistency with crustal, lithospheric, and mantle deformation and deformation in the subduction channel over geological time scales.…”

“…We apply the 2D geodynamical subduction and seismic cycle (SC) model from van Zelst et al (2019) to inform realistic 3D dynamic rupture (DR) megathrust earthquake models within a complex, self-consistent subduction setup along with their consequent tsunami, following the subduction to tsunami run-up linking approach described in Madden et al (2020). In this study we introduce a number of important differences to previous work.…”

“…In contrast, we here constrain fracture energy independently from the long-term model. In Madden et al (2020), a different long-term geodynamic and seismic cycle simulation was used, specifically, assuming different shear moduli. We here change the geometrical 3D extrapolation of the 2D fault geometry compared to the large blind dynamic earthquake scenario of M W 9.0 of Madden et al (2020), to be consistent with empirical earthquake source scaling relations for M W 8.5 megathrust events (Strasser et al, 2010).…”