When a rigid, elastic oceanic plate subducts from a trench, an outer bulge is formed due to flexure of the elastic plate. In addition, rough seafloor topographic features caused by plate bending-related normal faulting, such as horst and graben structures, are observed in the vicinity of the trench axis.
(Above) Schematic illustration of plate subduction in the north-western Pacific margin.
(Bottoms) Bathymetric maps around the Japan trench at northern latitudes of 37-41 degrees (from off-Miyagi to–off-Aomori). Left bottom, water depth; middle bottom, inclination of slope; right bottom; aspect of slope.
* Bathymetric data are ETOPO1 (above), and a compilation of multi-narrow beam echo sounder data collected by Japan Coast Guard and JAMSTEC (bottoms).
(Illustration & Explanation: Gou FUJIE and Shigeaki ONO)
