3:30 PM - 4:45 PM
[SCG59-P12] Active shallow structures of the Nankai forearc region off Hyuga
Keywords:subbottom profiler, active flexure, active fault
We carried out deep-towed subbottom profiler (SBP) survey by ROV NSS (Navigable Sampling System) during R/V Hakuho-maru KH-15-2 cruise. High resolution profiling was successfully conducted by a chirp system of EdgeTech DW-106. The first target is the NNE-SSW trending Oyodo Knoll developed eastward of the Hyuga basin. The SBP shows the almost symmetrical ridge morphology cut by active flexures on both sides suggesting compressional deformation. Although faults are not detected at the surface sequence at least down to 60 meter except for two minor reverse faults, sediment thickness changes across the flexures indicate continuous deformation to the present. The second target is the western margin of the Hyuga basin where steep slopes suggestive of fault control are distributed from north to south. Two transects of SBP surveys are conducted at the southern and central regions of the western margin. SBP records of both transects show active flexures with relative landward uplift. The southern site is characterized by a V-shaped depression landward of the flexure and its sediment fill indicative of transtensional deformation. The central site also shows undulation of basin sedimentary layers landward of the flexure suggesting strike slip deformation. Our high-resolution subbottom profiles of the Hyuga forearc region revealed that the topographic framework have been formed by ongoing active deformations under high sedimentation rate.