Abstract
Elongated trough-like depressions were discovered on the shelf break, southwest off the Kyushu. Each depression is 200−250 meters in width, hundreds meters to 2 kilometers in length and 10−20 meters in relative depth. The depressions are discontinuously aligned for 18 kilometers parallel to the strike of the shelf slope. The shelf and upper shelf slope consist of a deposit of the Pleistocene Ito pyroclastic flow in origin. The distribution of the depressions and geological information indicate that the depressions are not any of erosional features by tidal currents or gravitational flows, but “crown crack”, which is a kind of tensional cracks on the top of a submarine slide body during the initial stage of sliding.
