[S-CG67_2AM2] 海洋底地球科学

[SCG67-P15_PG] 北西太平洋の深海底における音響特性評価

ポスター講演3分口頭発表枠

*沖野 郷子¹、本荘 千枝¹、町田 嗣樹²、及川 光弘³、中村 謙太郎⁴ (1.東京大学大気海洋研究所、2.早稲田大学創造理工学部、3.海上保安庁海洋情報部、4.東京大学工学系研究科)

キーワード：marine acoustics, muti-beam echo sounder, backscattering intensity, abyssal plain

The old seafloor covered by pelagic sediment has not attracted large scientific attention and remained untouched for many years, however, the recent studies on intra-plate volcanism as well as the increasing interest in deep-sea natural resources focus spotlight on the abyssal plains. We analyzed the multi-beam bathymetry, beam intensity, and side-scan images of abyssal plain in the northwestern Pacific, around the Minami-Torishima (Marcus) Island. The data were collected by Japan Coast Guard as part of Japanese EEZ survey and by R/V Yokosuka for decades. The beam intensity data from multi-beam echo sounder were processed to create a backscatter mosaic without geometric distortion. The mosaic shows a large variation of acoustic characteristics in whole study area. The high backscattering areas at the foot of large seamounts likely reflect the distribution of volcaniclastic sediments and debris. We can also recognize another type of high backscattering areas in flat seafloor, where neither remarkable seamounts nor knolls exist. The latter type partly corresponds to the area where the high concentration of rare-earth elements were reported and may suggest a thin cover of uppermost soft sediment layer. We try to integrate the backscattering mosaics and the statistic analysis of bathymetry and to establish a new method of acoustic characterization of abyssal plain. We also plan to compare our results with piston core samples as ground references and to discuss the sedimentation process and the relationship with intra-plate volcanism on old seafloor.