This paper presents results of an interdisciplinary investigation of the relation between fluids, fluid flow, and deformation in the toe region of the Nankai accretionary prism. The techniques include thin-section petrography, SEM, TEM and microprobe analyses, and X-ray computed tomography as well as laboratory experiments. Together, the data suggest three structural/hydrologic regimes within the prism. These are: (1) the accreting sediments above the décollement zone, (2) the décollement zone, and (3) the underthrust sediments. The regime above the décollement is characterized by sediments that are progressively dewatered through both a penetrative fabric and a pervasive, but apparently poorly interconnected, set of core-scale deformation structures. The décollement is characterized by a relatively high density of structures/meter and is considered to be a regime of low stress but frequent failure. Hydrologically the décollement retards the vertical flow of fluids and enhances the potential for overpressuring in the footwall. Finally, the footwall regime contains very few tectonic structures and is structurally isolated from the stresses related to plate convergence. This regime provides an important component to the tectonics of the Nankai prism, however, because it supplies the overpressured fluids that cause the d?collement to fail at relatively low shear stresses.

Supplement to: Byrne, Timothy; Maltman, Alex J; Stephenson, Emma; Soh, Wonn; Knipe, Rob (1993): Deformation structures and fluid flow in the toe region of the Nankai accretionary prism. In: Hill, IA; Taira, A; Firth, JV; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 131, 83-101