3D bathymetric image of the Nansei-Shoto Trench and its vicinity

Abstract

We interpreted seafloor topography using anaglyph images based on 150 mDEM processed from multi−beam bathymetric data collected by Japan Coast Guard and JAMSTEC in the area around Nansei−Shoto Trench, and made more precise submarine active faults map than that mapped by previous workers. In the southern part of the trench, trench−parallel northwest−dipping thrusts form extensive fault scarps on the lower part of landward trench, indicating that repeated large earthquakes and tsunamis have been generated along the trench. Some of the scarps extend over several hundred km and the longest one is about 700 km. They are candidates for gigantic earthquake and tsunami generators. In the northern part, such scarps were scarcely recognized close to the trench axis due to collision of several bathymetric highs, while active reverse faults form distinctive fault scarps on the upper slope of the landward trench. They locate close to the island shelf, and are probably responsible to the uplift of islands forming Pleistocene and Holocene coastal terraces.