A subducting seamount beneath the Nankai accretionary prism off Shikoku, southwestern Japan

A multi-channel seismic (MCS) reflection survey was conducted to study the structure of the Nankai convergent margin off Shikoku Island in July 1997. Based on reflection characteristics, we could identify three major seismic reflection units, i.e., Units A, B, and C. The MCS data as well as swath-ba thymetric data reveal a buried circular seamount subducting beneath the Nan kai accretionary prism. The subducting seamount is responsible for deformat ion of the accretionary wedge, resulting in a compressed uplifted sediment knell and many steep escarpments with NE-SW strike. A possible thrust fault was identified on the seaward flank of the seamount, indicating compressiv e deformation. A tectonic model for subduction of the seamount is presented based on the interpretation of the MCS data.