[SSS06-P01] Crustal structure in the Nankai Trough seismogenic zone based on renewed depth images and seismic attribute analysis
Keywords:Nankai Trough seismogenic zone, crustal structure, reflection seismic, seismic attribute
As a result of our investigation, deformed structure within the inner accreted sediments and its relation with the megathrust fault are clearer than before. Anticlines are identified just below the Kumano forearc basin and fragmented reflections can be seen below the anticlines. Characteristic patterns of folds can be recognized on the horizontal section of the coherence cube, which are corresponding to the anticlines on the vertical sections. These reflection features imply development of fold structures due to thrust faults with branched minor faults. In the reprocessed 2D section, curved reflectors with stepwise displacement are imaged in the region of 4 - 6 km depth. These reflectors may represent multiple thrust faults with back-thrusts, and the thrust faults are consistent with the structural features in the 3D images. The detachments of the thrust faults seem to converge to wavy points on the megathrust fault surface. Furthermore, details of deformation and fracture in the outer accretionary prism are imaged clearer than the previous images. Lithological boundaries with displacement along imbricated thrusts can be traced beyond the fault, and conjugate faults due to horizontal compression which cut the in-sequence thrusts are recognized on the horizontal section from superimposed view of the coherence and dip angles. Reflectors within underthrusted sediments beneath the imbricated thrust layer are clearly imaged. Some of the reflectors can be identified as parts of detachment of the thrust faults. The topographic relief of the oceanic crust should be considered when the deformed structures in the overburden sediments and distribution of décollement are revisited.
This research is supported by JSPS KAKENHI (JP15H05717).