Abstract
The main objectives of our research are to: (1) examine and interpret the mechanisms of subduction zone earthquakes around Japan; and (2) plan and carry out geophysical cruises and make related geophysical and geological observations of the trenches and associated subduction zones around Japan in support of (1). In order to fulfill the above objectives, our research focuses on the dynamics of deep-sea trenches using multi-channel seismic reflection and ocean-bottom seismometer methods, and the integration of these and existing data via sophisticated database procedures. Marine geophysical data of bathymetry, geomagnetics, gravity, heat-flow measurements, and crustal structure have been acquired and integrated since the 1960s internationally by oceanographic institutions including the Japan Marine Science and Technology Center (JAMSTEC). We are developing a global marine geophysical database system and making compilations and analyses of these data. Several research vessels in JAMSTEC are equipped with various advanced marine geophysical instruments. Geophysical data sets obtained during cruises are entered into the JAMSTEC database after appropriate editing and formatting. The database is expanded as additional data are collected, employed for realistic parameters in modeling and simulation studies, and used as the basis for planning additional cruises in areas with sparse data. We are in the process of compiling crustal structure, marine geomagnetic and gravity data off northeastern Japan to clarify the geophysical characteristics of magnetic lineations on the subducting plate and trench gravity anomalies in that region. The characteristics of different geophysical properties are related to the origins of tectonic components, their subsequent deformation and other possible processes of subduction. We will continue to examine several subduction models as additional data are obtained during future Frontier surveys.
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