Investigation of the imbricated system along the Muroto Transect and its relationship to the subducting Muroto Seamount

This thesis investigates a series of seismic reflection lines across the Nankai Trough called the Muroto Transect. The 3D pre-stack depth-migrated data were acquired off Shikoku Island, Japan and covers the seaward portion of the Nankai Trough accretionary prism. Determination of shortening and implications of Coulomb Wedge Theory were evaluated. The lines provides an opportunity to study deformation effects, structures, and extent of shortening of sediments being subducted-accreted to the hanging wall as well as along strike variations and influences of the subducting seamount deformation in the accretionary prism. Shortening was measured across 3 lines and was estimated to vary between 20 and 25.6 percent. The coulomb wedge taper varied from 3.4° and 3.9°. These values of taper show that the Nankai accretionary prism at the Muroto Transect lies on the weak décollement zone. Based on the percentage of shortening amount in distance of three lines, the percentage of shortening in distance of the prism increase in the direction of southwest to northeast. The angle of surface slope and dip of décollement are determined for five lines. The tapers of the lines increase in the direction of southwest to northeast (3.4-3.9). The internal friction (μ) and internal effective friction ( μ_beff) coefficients calculated decrease in the direction of southwest to northeast from 0.25 to 0.176 and 0.07 to 0.054 respectively. Detailed investigation over the imbricate system of the Muroto Transect suggests that there is a little to no effects presented by the subducting Muroto Seamount. Based on the seismic interpretation, the contact between the seamount and the accretionary prism was illustrated below the interpreted subduction channel, and the imbricate thrust system detached to the décollement without any impact of the seamount in the down-going plate. Based on the result of structural restoration and Coulomb Wedge Theory, the present imbricate system has developed with no apparent inherited or lingering effect from the seamount subduction, as the seamount upper contact lie below the subduction channel as interpreted, and wedge strength indicates very little change from the interpreted transect along strike outside the zone of seamount subduction.