Crustal deformation and stress localization in Kanto-Tokai, central Japan revealed by GPS

Abstract

Horizontal deformation associated with plate interaction in the Kanto-Tokai district, central Japan has been determined using the Japanese permanent Global Positioning System (GPS) array with an accuracy of better than ± 2.5 mm yr−1. Previous analysis of the GPS observations mainly focused on the pattern of deformation or strain and did not attempt to assess stress change associated with plate subduction. In this study, using the GPS observations and the geometry of subducting slabs as constraints, we constructed a 3-D kinematic model to simulate the subduction of the Philippine Sea Plate at the Suruga and Sagami troughs and the Pacific Plate at the Japan trench. The model incorporating the effects of major plate driving forces (ridge push, slab pull and drag force) associated with plate subduction provides an overall fit to the horizontal deformation observed by GPS during 1996–2001 in the Kanto-Tokai region. The horizontal motion of the Philippine Sea Plate is estimated to be 41 ± 5 mm yr−1 (60 ± 5°NW), consistent with that (ca 43–50 mm yr−1) inferred from earthquake slip vectors and geological data. The horizontal motion of the Pacific Plate is estimated to be 78 ± 6 mm yr−1 (84 ± 5°NW), close to that (ca 73–79 mm yr−1) deduced from earthquake slip vectors. After extracting the regional deformation associated with subduction of the Philippine Sea and Pacific Plates from the GPS observations, two types of motion trends are revealed for the northern part of the Kanto-Tokai region. The southeastward motion of the GPS stations revealed by the residual displacements in northern Tokai indicates a possible resistance force from the north. In northern Kanto, the west-southwestward residual motion of the GPS stations indicates the motion of the North American Plate relative to the Eurasian Plate. The distinct boundary between these two different types of motion trends provides strong support for the presence of the North American Plate in the region, which demonstrates that the model has delineated the main characteristics of plate interaction. Further, a stress analysis indicates that stress is accumulating on the Suruga trough at a rate of approximately 0.7 bar yr−1, at a depth of 15 km. Our results indicate that the pattern of stress localization is mainly controlled by the kinematic characteristics of the subducted slabs (geometry and slip distribution) and the persistent stress concentration is responsible for repeated large interplate earthquakes in the region.