10:00 AM - 10:15 AM
[SCG61-17] Tectonics and Seafloor Topography around Japan
In this study, we present a new approach to evaluate the stress field around Japan by utilizing the characteristic orientation of the seafloor topography. The shape of volcanic complex is influenced by the crustal stress field, and its orientation typically aligns with the direction of maximum compressive stress (Nakamura, 1994).
We use the seafloor topography data of Japan Oceanographic Data Center provided by the Japan Coast Guard. For each topographic features at the scale of 4-9 square kilometers, we approximate the isobath with an ellipse to quantify. The major axis orientations and flattening ratios. We then evaluate the average azimuth angle of bathymetry for each one-degree grids in latitude and longitude.
As a result, we confirmed that the long-axis azimuths around the Izu Islands are oriented in the northwest and northeast directions. This orientation may be attributed to the northwestward subduction of the Philippine Sea Plate and the presence of a triple junction, which creates a complex stress field. The stress field estimated from the major axis orientation was consistent with the stress field observed based on the classic tensor inversion. In Ryukyu, the long-axis orientation was found to be parallel to the Okinawa Trough. This alignment may be due to the formation of Ryukyu through back-arc spreading at the plate boundary between the Philippine Sea Plate and the Eurasian Plate. The stress field is consistent with the east-west-compression stress field obtained through the stress tensor inversion. Furthermore, we confirmed that the long-axis azimuth is parallel to coastline in the Japan Sea. However, the inferred stress field looks different from the current stress field. This discrepancy is considered to be resulted from the predominance of the basin inversion structure within the sedimentary layer, which is formed due to the east-west compression field started 3 million years ago after the cessation of Japan Sea expansion 15 million years ago.
We use the seafloor topography data of Japan Oceanographic Data Center provided by the Japan Coast Guard. For each topographic features at the scale of 4-9 square kilometers, we approximate the isobath with an ellipse to quantify. The major axis orientations and flattening ratios. We then evaluate the average azimuth angle of bathymetry for each one-degree grids in latitude and longitude.
As a result, we confirmed that the long-axis azimuths around the Izu Islands are oriented in the northwest and northeast directions. This orientation may be attributed to the northwestward subduction of the Philippine Sea Plate and the presence of a triple junction, which creates a complex stress field. The stress field estimated from the major axis orientation was consistent with the stress field observed based on the classic tensor inversion. In Ryukyu, the long-axis orientation was found to be parallel to the Okinawa Trough. This alignment may be due to the formation of Ryukyu through back-arc spreading at the plate boundary between the Philippine Sea Plate and the Eurasian Plate. The stress field is consistent with the east-west-compression stress field obtained through the stress tensor inversion. Furthermore, we confirmed that the long-axis azimuth is parallel to coastline in the Japan Sea. However, the inferred stress field looks different from the current stress field. This discrepancy is considered to be resulted from the predominance of the basin inversion structure within the sedimentary layer, which is formed due to the east-west compression field started 3 million years ago after the cessation of Japan Sea expansion 15 million years ago.