Subduction of transitional crust at the Manila Trench and its geophysical implications

Abstract The subducting South China Sea crust at the northern Manila Trench has been categorized as the transitional crust, which is a rifted, thinned continental crust. We tested the consequence of the subduction of transitional crust with a numerical dynamic model. Our numerical model indicates that, with subducting transitional crust, normal fault earthquakes underneath the accretionary prism would occur deeper and probably with larger magnitude. Normal fault earthquakes near the trench outer rise are usually shallower than 30 km depth around the world. A notable exception is at the northern Manila Trench where normal fault earthquakes around 40 km depth are common, which can be explained by our model. Our result indicates that the stress on the northern segment of the Manila Trench is relaxed, which is less likely to generate great megathrust earthquakes.