This study aims to describe the submarine geomorphology near the Kandamisaki-oki fault off the coast of the Sanin region and examine its development. The NW-SE trending Kandamisaki-oki fault is a series of fault scarps on the seafloor and is a northwestern extension of the onshore Kikukawa fault, an active sinistral strike-slip fault. Although the distribution and activity of the Kandamisaki-oki fault have been studied, the submarine geomorphology near the fault has been ignored.
This study produced a topographical anaglyph image using a 0.3-s-mesh digital elevation model that used point-cloud data obtained through a multi-beam acoustic survey by the Japan Coast Guard. The image was exaggerated vertically and overlapped with a relief map and an isobath. When viewed with red-cyan glasses, it enables easy identification of topographical features, such as submarine terraces and small fault scarps.
By interpreting the anaglyph, the submarine terraces were divided into six surfaces, named the S1, S2, S3, S4, S5, and S6 surfaces, in descending order. The angles indicating the paleo-shoreline behind the flat surface of each submarine terrace were at a depth of approximately 30m for S1, approximately 50m for S2, approximately 80m for S3, approximately 110m for S4, approximately 120m for S5, and approximately 130m for S6. In the study area, these depths were similar and correlated to the terrace surfaces around the Tsushima Strait and the Nanseishoto islands. Therefore, the submarine terraces in the study area developed in association with the global sea-level changes resulting from the changes in the volume of the glaciers since the last glacial period.