Megathrust Earthquake Potential of the Manila Subduction Systems Revealed by the Radial Component of Seismic Moment Tensors Mrr

Abstract

We undertook an investigation of the seismic behavior of large earthquake and estimated the crustal deformation state in the northern Philippine area in terms of the radial component of seismic moment tensors (Mrr) distribution. Based upon these two analyses, the seismic potential of the Manila Trench has been assessed. Regarding the seismic characteristics of large earthquakes, results show that both the overriding and the subducting plates are under compressive stress before the main large events but are characterized by an extensional regime after mainshocks. In the northern Manila Trench area, the broad zone of extensional seismic activity along the trench and its neighboring areas shows a stress environment distinct from that of the interseismic environment of large earthquakes, suggesting that the plates are in a relaxed state instead of accumulating tectonic stress. Thus, the coupling between the two plates could be weak. Along the central Manila Trench, even though only few extensional earthquakes occurred near the trench, numerous negative Mrr events in the overriding plate indicate that the crust is affected by a dilatational regime and also suggests a relatively low coupling environment. In the southern Manila Trench, with the exception of a few extensional events that occurred locally in the Central Valley Basin, most earthquakes show compressive mechanisms. We suggest that a relatively high plate coupling exists along this portion of the trench and results in stress accumulation not only along the plate interface but also in its vicinity, within the subducting and overriding plates.