Detecting The Missing Oceanic Supershear Earthquakes

Abstract:

Supershear earthquakes are of broad interest because they produce destructive ground shaking and their occurrence and sustained propagation give rise to important questions in rupture dynamics. Previously, only eight shallow supershear earthquakes have been reported with strong near- and/or far-field seismic evidence. In this talke, we report several previously undocumented oceanic supershear earthquakes based on rupture speeds determined by Slowness-Enhanced Back-Projection and far-field Rayleigh Mach wave identification. Our findings indicate that the oceanic supershear earthquakes are no less than their continental counterparts and increase the percentage of supershear earthquakes to 14.5% among all large shallow strike-slip events. We observe a wider range of stable supershear rupture speeds than theoretical predictions, possibly explained by the presence of fault damage zones and slip obliqueness. We attribute these new discoveries of supershear ruptures in nature to larger seismogenic width, bimaterial effect of oceanic-continental boundaries that promote both supershear transitions and propagations.