Japan Trench
Large magnitude and frequent earthquake activity occurring at the northern Japan Trench may be explained by variations in surface roughness of the subducting Pacific plate. Regions of smooth ocean floor subduction are correlated with typically large under-thrust earthquakes within the deeper part of the plate interface zone. No earthquakes have been observed or reported from the shallow aseismic zone of the north Japan Trench. Regions of rough ocean bottom subduction are correlated with large normal faulting earthquakes within the outer-rise region, along with larger tsunami earthquakes occurring at the shallow region of the plate interface (megathrust events) .