Geologic structure of the upper continental slope off Shikoku and Quaternary tectonic movement of the outer zone of southwest Japan

Abstract

The Quaternary tectonic movements were studied on the basis of marine seismic profiling data and sea-bottom samples in the upper continental slope off Shikoku, southwest Japan. Emerged marine terraces fringe the southern coast of Shikoku, and their height decreases to the northwest. The offshore geologic structure, onshore topography of Shikoku and emerged marine terraces can be simply interpreted by the growth of the two different undulations. It is inferred that the undulation having N-S directed axis has been growing under the E-W compressional stress field which is supported by focal mechanisms of earthquakes in the crust of Shikoku, and principal compressional stress presumably changed from N-S or NW-SE and E-W at the beginning of the Quaternary time in the whole of the southwest Japan. -from English summary