Tsunami excitation in the outer wedge of global subduction zones

Abstract

The world's most devastating local and ocean-wide tsunamis are generated by subduction zone earthquakes, but the mechanisms for powerful seafloor uplift and tsunami generation during seismic rupture propagation remain poorly understood. In particular, great earthquakes near the trench can generate outsize tsunamis that rival those produced by giant trench-breaking ruptures. Solving this conundrum is key to better assessing seismic and tsunami hazards at subduction zones. Here, we inspect high-resolution bathymetry, seismic reflection profiles, and tsunami-earthquake rupture models at global subduction zones to identify the structural control on tsunami excitation by coseismic seafloor uplift. We find that tsunami run-ups of trench-breaking ruptures correlate with the width of the outer wedge of the frontal accretionary prism, which consists of active imbricate or conjugate faults above the shallow megathrust. The prevalence of high-angle faults in the outer wedge provides the mechanism for more efficient seafloor uplift and thus tsunami wave excitation than coseismic slip on the shallow décollement. We calibrate a power-law relationship with outer-wedge width and seismic moment to estimate the maximum tsunami run-up along major subduction zones. The tsunami excitation potential is among the highest at the northern Sumatra (Indonesia), Hikurangi (New Zealand), and western Makran (Iran) accretionary margins, and the lowest at the Costa Rica and Valdivia (Chile) erosive margins. The structural control of tsunami excitation is important to characterize the rupture style and tsunami magnitude of future seismicity at subduction zones, offering crucial information for seismic and tsunami hazard preparedness and rapid run-up assessment during the early-warning stage, especially at well-identified seismic gaps.