2008年4月30日

木村 学 氏　(地球惑星科学専攻)

Activities of megasplay and frontal thrust faults at Nankai accretionary complex off Kumano

During the Expedition 316, drilling was conducted at two sites in the megasplay region, one within the fault zone and one in the slope basin seaward of the megasplay. Two sites were also drilled within the frontal thrust region. Site C0004 is located along the slope of the accretionary prism landward of the inferred intersection of the megasplay fault zone with the seafloor. Drilling at this site examined the youngest sediments on the slope overlying the accretionary prism; these sediments consist of slowly deposited marine sediments and redeposited material from further upslope. This redeposited material provides information about past slope failures, which may be related to past megasplay movement, earthquakes, and tsunamigenesis. The cores from the fault zone record a complex history of deformation based on structural observations and two age reversals suggested by nannofossil evidence. The sediments underneath the fault zone were sampled to understand their deformation, consolidation, and fluid flow history. Drilling at Sites C0006 and C0007 examined the frontal thrust region. Site C0006 captured several fault zones within the prism before being halted by drilling conditions. Site C0007 successfully drilled through the plate boundary frontal thrust, and successfully recovered thrust fault material ranging from breccia to fault gouge.