Stress, rigidity and sediment strength control megathrust earthquake and tsunami dynamics

Megathrust faults host the largest earthquakes on Earth, which can trigger cascading hazards such as devastating tsunamis. Determining characteristics that control subduction-zone earthquake and tsunami dynamics is critical to mitigate megathrust hazards but is impeded by structural complexity, large spatio-temporal scales and scarce or asymmetric instrumental coverage. Here we use high-performance computing multi-physics simulations to show that tsunami genesis and earthquake dynamics are controlled by along-arc variability in regional tectonic stresses together with depth-dependent variations in rigidity and yield strength of near-fault sediments. We aim to identify dominant regional factors controlling megathrust hazards. To this end, we demonstrate how to unify and verify the required initial conditions for geometrically complex, multi-physics earthquake–tsunami modelling from interdisciplinary geophysical observations. We present large-scale computational models of the 2004 Sumatra–Andaman earthquake and Indian Ocean tsunami that reconcile near- and far-field seismic, geodetic, geological, and tsunami observations and reveal tsunamigenic trade-offs between slip to the trench, splay faulting and bulk yielding of the accretionary wedge. Our computational capabilities render possible the incorporation of present and emerging high-resolution observations into dynamic-rupture-tsunami models and will be applicable to other large megathrust earthquakes. Our findings highlight the importance of regional-scale structural heterogeneity to decipher megathrust hazards.