[S-CG49] Structure, evolution and deformation of island arcs associated with subduction processes

[SCG49-02] Stress loading on offshore faults in the Sea of Japan due to the interplate processes along the northwest and southwest Japan arcs

*Akinori Hashima¹, Hiroshi Sato¹, Tatsuya Ishiyama¹, Andrew M. Freed², Thorsten W. Becker³ (1.Earthquake Research Institute, The University of Tokyo, 2.Purdue University, 3.The University of Texas at Austin)

Keywords:Stress loading, Northeast Japan arc, Southwest Japan arc, Source fault, Finite element method, Crustal deformation

In the Sea of Japan, several damaging earthquakes occurred such as the 1964 Niigata, the 1983 Sea of Japan, the 1993 Southwest Hokkaido earthquakes. In the coastal region, not only damages from strong motions but also risks of tsunamis are concerned. Recently, the distribution of possible source faults in the Sea of Japan from geophysical explorations. It is important to estimate the stress accumulation on these source faults for assessing seismic risks. In this study, we estimate stress loading due to the dominant interplate process along the Northeast and Southwest Japan arcs using our finite element model. The model is constrained by the data from the dense GPS observation network over the Japanese islands.

In our previous studies, we construct a 3-D finite element model including the Japanese islands. This model consists of the Eurasia, Pacific and Philippine Sea plates. The plate boundaries are determined by the previous studies based on distribution of the interplate earthquakes. The plate boundary shallower than depth of 80 km is divided into ~3000 subfaults to generate Green’s functions. The model includes viscoelastic property in the asthenosphere to treat the long-term process.

Using the model, we obtain distribution of slip-rate deficit (locking) on the plate boundaries. Then, we calculate the Coulomb stressing rate on the source faults in the Sea of Japan. The long-term locking along the Nankai trough and the Kuril trench have strong influence on the Sea of Japan, resulting in the widely positive Coulomb stressing rate on the source faults along the north coast of from the Kyushu island to the central Japan and along the west coast of Hokkaido, which is bringing those faults forward to rupture. On the source faults along the west coast of Tohoku region, the Coulomb stressing rates was positive before the occurrence of the 2011 Tohoku-oki earthquake, but they have been negative since then. The effect of the Sagami trough is limited but can been seen on the source faults along the coast of Niigata and Hokuriku. In particular, the offshore region along the coast of Niigata and Aomori is transitional zone between the Tohoku-oki earthquake and the locking of the Nankai trough, and between the Tohoku-oki earthquake and the locking of the Kuril trench. It is important to make clear the contribution of their effects and verify them with the seismic activities.