Hidden Roughness of Subducting Seafloor and Implications for Megathrust Seismogenesis: Example From Northern Manila Trench

Abstract

AbstractA smooth subducting seafloor usually leads to a smooth megathrust, which promotes great earthquakes. We present a case study at the northern Manila Trench to emphasize that the process depends also on sediment accretion and deformation. Here, a very rugged igneous basement is hidden beneath a smooth sediment cover on the incoming seafloor. Seismic imaging indicates that most of the sediment is scraped off at the trench, resulting in an uneven décollement interrupted by partially exposed subducted seamounts. New thermal models confirm the presence of large frictional heating, also consistent with a rough and strong megathrust. Our findings in conjunction with the low degree of megathrust locking reported in the literature are compatible with the notion of strong creep. Consequent implications to regional seismic and tsunami hazards call for further investigations, especially with new seafloor geodetic monitoring and improved paleoseismic studies.