Modeling Megathrust Earthquakes Across Scales: One‐way Coupling From Geodynamics and Seismic Cycles to Dynamic Rupture

Abstract

Taking the full complexity of subduction zones into account is important for realistic modeling and hazard assessment of subduction zone seismicity and associated tsunamis. Studying seismicity requires numerical methods that span a large range of spatial and temporal scales. We present the first coupled framework that resolves subduction dynamics over millions of years and earthquake dynamics down to fractions of a second. Using a two-dimensional geodynamic seismic cycle (SC) model, we model 4 million years of subduction followed by cycles of spontaneous megathrust events. At the initiation of one such SC event, we export the self-consistent fault and surface geometry, fault stress and strength, and heterogeneous material properties to a dynamic rupture (DR) model. Coupling leads to spontaneous dynamic rupture nucleation, propagation, and arrest with the same spatial characteristics as in the SC model. It also results in a similar material-dependent stress drop, although dynamic slip is significantly larger. The DR event shows a high degree of complexity, featuring various rupture styles and speeds, precursory phases, and fault reactivation. Compared to a coupled model with homogeneous material properties, accounting for realistic lithological contrasts doubles the amount of maximum slip, introduces local pulse-like rupture episodes, and relocates the peak slip from near the downdip limit of the seismogenic zone to the updip limit. When an SC splay fault is included in the DR model, the rupture prefers the splay over the shallow megathrust, although wave reflections do activate the megathrust afterward.

How Sediment Thickness Influences Subduction Dynamics and Seismicity

“…Due to the major numerical challenge of resolving both millions of years and subsecond time scales, events have an unrealistically long duration, as a large 5 year time step limits computations. This does not allow us to resolve earthquake nucleation and dynamics, which could affect the recurrence interval and slip distribution (van Zelst et al., 2019). However, the main findings of this paper are determined by long‐term characteristics that are not affected by the limited time resolution of our approach.…”

Earthquake Cycles in Fault‐Bend Folds

“…The mechanical conditions that lead to a wide range of earthquake sizes along a plate boundary and the role of fault geometry in earthquake segmentation remain poorly understood. Fault bends are relevant to earthquake initiation and termination processes (King & Nábėlek, ; King, ), and studies of dynamic earthquake ruptures with geometric complexities have shown significant off‐fault deformation (Aochi et al, ; Duan & Day, ; Kase & Day, ; Preuss et al, ; van Zelst et al, ; Zhang et al, ). Previous work on the dynamics of ruptures at fault bends is often limited to single‐cycle ruptures (Aochi et al, ; Lozos et al, ; O'Reilly et al, ; Poliakov et al, ; Rousseau & Rosakis, ), but a multi‐cycle approach is required to discuss rupture dynamics and seismic supercycles (e.g., Dal Zilio et al, ; Herrendörfer et al, ; Ong et al, ).…”

Dynamic Fault Interaction during a Fluid-Injection-Induced Earthquake: The 2017 Mw 5.5 Pohang Event

“…All faults are exposed to the same local stress regime while experiencing varying ratios of shear and normal loading, depending on their orientation towards this loading. Even a small change in fault geometry (e.g., in strike, dip, size, and the angle between fault planes) strongly affects the dynamic rupture result (e.g., Yamashita and Umeda, 1994;Aochi et al, 2005;Bhat et al, 2007;Ulrich et al, 2019a;van Zelst et al, 2019), as illustrated when comparing Model 1F and Model 2F. We point out that trade-offs between the inferred stress state and fault geometry can be readily explored if new observations become available.…”