Estimation of paleo-permeability around a seismogenic fault based on permeability tensor from observable geometric information of quartz veins

Abstract

AbstractThe mineral veins formed by filling tensile cracks record the accumulation of past hydraulic activities such as fluid migration in the damage zones of a fault. The purpose of this study is to estimate the fluid flow behavior around thrust faults using a three-dimensional permeability tensor from the geometric information of mineral veins. Here, the estimated permeability represents paleo-permeability when the mineral veins were open fractures. We attempted to estimate paleo-permeability in the damage zone around the Nobeoka Thrust fault by applying Oda’s permeability tensor theory, as determined from the geometric information of mineral veins observed in the outcrop. In addition, in situ data acquisition and analytic techniques were developed to estimate a three-dimensional paleo-permeability tensor, and we estimated the paleo-permeability around the Nobeoka Thrust. As a result, the paleo-permeability tensor could be estimated from the geometric information of the mineral veins in the outcrop, which helped clarify the migration of fluids around the fault. Our results show that the paleo-permeability anisotropy and paleo-permeability value changed with distance from the fault core on the footwall; in particular, the maximum paleo-permeability increased from the damage zone to the fault core. In addition, the direction of maximum paleo-permeability shows that the fluid in the footwall migrated toward the fault plane or to the hanging wall immediately after the earthquake. Graphical Abstract