17:15 〜 19:15
[SCG55-P23] Shallow submarine structure around the Danjyo Basin, Okinawa Trough, based on the Sub-Bottom Profiler Survey
キーワード：Okinawa Trough、Back arc、Submarine landslide
The Okinawa Trough is a back-arc basin that is forming on the back-arc side of the Ryukyu Arc where the Philippine Sea Plate is subducting. The northernmost part of the Okinawa Trough has garnered attention as it is believed to be in the early stages of back-arc basin expansion. This region contains the Danjo Basin, which reaches depths of up to 800 meters. In the southern section of the basin, a submarine escarpment with a height of approximately 100 meters is present, likely formed by active faulting. To understand the frequency of earthquakes and the potential for tsunami generation in the Danjo Basin area, it is crucial to examine the shallow subsurface sedimentary structures. In this study, we conducted a survey using a sub-bottom profiler in the waters surrounding the Danjo Basin. The survey was performed in 2022 utilizing the training vessel Shinyo-maru of the Tokyo University of Marine Science and Technology.
Analysis of the obtained reflection profiles revealed numerous faults. By mapping the faults observed across survey lines, it was determined that they predominantly exhibit northeast-southeast strike orientations. Additionally, positive flower structures, indicative of strike-slip faulting, were also identified. These findings suggest that while the northern Okinawa Trough is generally characterized by an extensional stress regime, localized compressional stress conditions also exist. Moreover, in the northern part of the Danjo Basin, we identified distinctive structural features that are thought to have resulted from multiple submarine landslide events. These findings imply that future seismic activity in the Danjo Basin region may trigger submarine landslides.
Analysis of the obtained reflection profiles revealed numerous faults. By mapping the faults observed across survey lines, it was determined that they predominantly exhibit northeast-southeast strike orientations. Additionally, positive flower structures, indicative of strike-slip faulting, were also identified. These findings suggest that while the northern Okinawa Trough is generally characterized by an extensional stress regime, localized compressional stress conditions also exist. Moreover, in the northern part of the Danjo Basin, we identified distinctive structural features that are thought to have resulted from multiple submarine landslide events. These findings imply that future seismic activity in the Danjo Basin region may trigger submarine landslides.