| We document regional and local variations in basement relief, sediment thickness, and sediment type on the northern Philippine Sea Plate using high-resolution seismic reflection survey. In this dissertation, I present results of three different projects, examining variations in the initial stage of the inputs to the Nankai Trough subduction zone and their effect on the toe structure of the overlying accretionary prism. Key geological parameters will include the distribution of turbidite depositional system in the Miocene and its facies architecture, diagenesis of mixed terrigenous and hemipelagic sediments overlying the basement relief. I defined three provinces (Western, Central, Eastern) on the northern Philippine Sea plate based on basement relief and examined their effect on sediment thickness and sediment type. Variations in the incoming sediment type comprise three major sedimentary units defined by ODP sites and four classes of seismic sequences along the Nankai Trough. Focusing this study on an isolated topographic high, Kashinosaki Knoll (KK), which influences sedimentation in the Eastern Province, seismic data demonstrate that the formation of KK and historical sedimentary succession differs over each basement slope. The lower portion of the sedimentary section is characterized by a package of high amplitude continuous reflections (LSB-T subunit) that lap onto steep basement slopes (∼20-30°) but are parallel to the gentle basement slopes (∼5-10°). These results indicate that turbidite deposition in the Miocene occur over gentle basement slopes in the Eastern Province. Accretionary prism's morphology, deformation pattern, and taper angle are best explained by the initial condition of the accreted sediment thickness, underthrust sediment type, and local basement relief on the subducting plate. We use Coulomb wedge theory to relate the various structural styles, such as the geometry of imbricate thrusts, to the wedge taper angle and friction properties. The taper angle correlates with the thickness of accreted sediment, effective basal friction coefficient, and the underthrust sediment type. Variations in sediment classes characterizing the incoming sediment heterogeneity may be a strong cause for the variation in frictional properties along the base of the accretionary prism, and therefore the plate boundary. |
