Numerical modelling of the relationship between the present tectonic stress field and the earthquakes in the Western Pacific Subduction Zone

Abstract

AbstractThe tectonic stress field of the Western Pacific Subduction Zone (WPSZ) has been affected by the interaction among the Euro‐Asian, Philippine and Pacific Plates, and the effect is manifested by the occurrence of huge earthquakes in this region. Here, using numerical simulation of the finite element method, attempts were made to evaluate the NW‐directed subduction of the Western Pacific Plate on the three secondary subduction zones, namely the Japan Subduction Zone, the Izu‐Bonin Subduction Zone and the Mariana Subduction Zone. In these zones, the structural geometry and viscoelastic property of the model were determined, as well as two main megathrust fault planes identified, by means of a comprehensive structural analysis of tomography and Crustal 2.0 data. This study shows that the tectonic stress field and earthquakes in the three secondary subduction zones have different distribution features under continuous NW‐directed subduction of the Western Pacific Plate; i.e. (1) the strong coupling area in the Japan Subduction Zone reflected subducted seamounts, ocean ridges or other topographic highs that control the frequent occurrence of historical large earthquakes and stress concentration; (2) in Izu‐Bonin Subduction Zone, there were fewer earthquakes compared with the Japan Subduction Zone, the reason for this kind of distribution is that the contact area and properties have been changed between the subducting Pacific Oceanic Plate and the overlying Philippine Oceanic Plate; and (3) earthquakes that happened in the Mariana Subduction Zone have complicated types, including thrust‐type, normal‐type and strike‐slip‐type earthquakes, which are triggered by the subducting and retreating of the Pacific Oceanic Plate, and an angular difference between the subducting direction of the Pacific Oceanic Plate and the strike of the Mariana Trench. In summary, formation of differences among the tectonic stress field and earthquake distribution of the three subduction zones are correlated not only to the geometrical structures of the major faults but also to the subducted seamounts and the strike directions of the trenches. Copyright © 2016 John Wiley & Sons, Ltd.