Coupled fluid flow and deformation modeling of the frontal thrust region of the Kumano Basin transect, Japan: Implications for fluid pressures and decollement downstepping

Abstract

Results of coupled fluid flow and deformation modeling illustrate the influence of frontal thrust slip on excess pore pressures and decollement downstepping in the Kumano Basin transect, offshore Japan. Although permeable trench sediments and a buried sandstone layer provide potential fluid escape pathways, the numerical modeling suggests that excess pore pressure could build beneath the frontal thrust within hemipelagic clay of the Shikoku Basin facies. Simulated excess pore pressures range between 45% and 77% of the overburden weight 3 km landward of the deformation front, and are very sensitive to the permeability of the Shikoku Basin clay and the coefficient of friction of the fault zone. Excess pore pressures increase as the fault coefficient of friction is increased, suggesting that volume change due to shear within the footwall sediments is an important contributor to excess pore pressures. Raising the coefficient of friction also increases shear within the sediments beneath the fault zone, suggesting downward migration of the decollement zone. This shearing focuses in the weaker Shikoku Basin clays rather than an underlying turbidite unit, suggesting that lithologic differences play an important role in controlling deformation location.