HR: 09:15h
AN: T41A-06    [PDF]
TI: Kumano Seismogenic Zone Imaging and Splay Fault Property
AU: * Kuramoto, S
EM: s.kuramoto@jamstec.go.jp
AF: CDEX, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Okano, T
EM: okanot@jamstec.go.jp
AF: CDEX, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Hashimoto, T
EM: hashimot@jamstec.go.jp
AF: CDEX, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Tanaka, H
EM: tanaka-h@jamstec.go.jp
AF: CDEX, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Taira, A
EM: ataira@jamstec.go.jp
AF: CDEX, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AB: Splay faults or out-of-sequence thrusts (OOSTs) are prominent structure in the Nankai accretionary prism. The splay faults merging to the plate interface between the subducting Philippine Sea plate and the overriding Eurasian plate. The contact area of the splay faults and decollement plane may be a possible up-dip limit of the seismogenic zone from geological interpretation point of view. The splay faults are not continuously traced nearly parallel to the trough axis. The discontinuity of splay fault system coincides with the basement structure from magnetic anomaly map. The faults are recognized as the outer-arc-high in the Kumano accretionary wedge. The splay fault system has an important scientific target that will be clarified by drilling. A new bathymetric survey and dive observations by manned submersible are carried out in the Kumano accretionary wedge. Basic morphological interpretation and dive observations give a new insight of tectonic framework of the Kumano area. Prominent splay fault system shows transpressional fault system and associated by active folding and faulting structures. One of the splay faults shows dextral slip phenomena from en-echelon structural interpretation. Several seepage sites are discovered along the splay faults. Preliminary chemical analysis of sediment pore fluids on the splay fault shows up to 10 % depletion of chloride concentration compare with bottom seawater and extremely high methane concentration of more than 600 umol/kg (Toki et al., in prep.). A significant gamma-ray anomaly also discovered from the same site (Ashi et al.). These data suggest that the origin of fluid is significantly deep and the fluid may flow along the splay fault. A recent Tsunami inversion study suggests that the rupture area during the last large earthquake (Tonankai, 1944) spread over even the splay fault system area. The splay faults show significant differences of activities from structural interpretation of each fault. The lower fault is cut by upper one and covered by slope sediments that are not deformed. This phenomenon is confirmed by surface observations by submersibles and deep-towed camera surveys. Recent MCS survey of the JAMSTEC revealed extremely clear image of plate boundary faults between the subducting Philippine Sea plate and the Eurasian plate in the Kumano area. One of the prominent features of plate boundary at near proposed up-dip limit of seismogenic zone is the highly reflective (positive polarity) splay faults. The new data will be presented and discussed the property.
DE: 1645 Solid Earth
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935)
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting