Bathymetric, Subsurface, and Gravity Survey off the Sada-misaki Peninsula, the Seto Inland Sea

• Published in: JAMSTEC REPORT OF RESEARCH AND DEVELOPMENT Vol. 27; pp. 13 - 25
• Main Authors: Kanamatsu, Toshiya, Fujiwara, Toshiya, Kasaya, Takafumi
• Format: Journal Article
• Language: English; Japanese
• Published: Yokohama Japan Agency for Marine-Earth Science and Technology 01.09.2018; Japan Science and Technology Agency
• Subjects: Bathymetry; Geologic depressions; Gravity Anomaly; Median Tectonic Line; Ocean floor; Pleistocene; Quaternary; Sada-misaki Peninsula; Sand; Sub-bottom Profiling; Tidal currents
• ISSN: 1880-1153; 2186-358X
• DOI: 10.5918/jamstecr.27.13

We conducted a bathymetric, subsurface, and gravity survey off the Sada-misaki Peninsula aboard the R/V Shinsei-maru KS-16-E01 cruise. The objective of the survey is detailed mapping and collection of basic geological information about the western end of Median Tectonic Line (MTL) active fault zone which is inferred to be located in the Seto Inland Sea. In the eastern side of the survey area, the bathymetry is characterized by sand wave structures. These structures are thought to be formed by strong tidal currents. In the western side of the survey area, the seafloor is rather smooth without the sand wave growth. Uneven topography and depressions probably reflect the MTL active fault zone. The bathymetry is considered to be formed by lateral fault movements. In the western side of the survey area, acoustic wave reflections of the sub-bottom profiling interpreted as a boundary between Quaternary and Pleistocene sedimentary layers were identified. The sedimentary layers were vertically displaced probably caused by faults. The MTL is associated with a steep gradient zone of gravity anomaly. There is positive anomaly along the shoreline in the southeastern side, and the gravity anomaly decreases across the tectonic line to negative gravity anomaly in the northwestern side. The gravity anomaly is suggested to reflect a deeper basement structure beneath the subsurface sedimentary layer. The basement structure inferred from the gravity anomaly profile is consistent with the half-graben crustal structure formed by the listric curving fault.