Stress tensors at the toe of the Nankai accretionary prism: an application of inverse methods to slickenlined faults

Abstract

Drilling at Site 808 (ODP Leg 131) provided an extensive record of the discrete brittle structures (small faults and shear bands) at the toe of the Nankai accretionary complex. Brittle failure is occurring throughout the hole, although most of the deformation has been observed between the frontal thrust and the decollement (from 365 to 963 mbsf). Brittle failure occurs in the turbiditic trench fill (0 to 600 mbsf) but also in the ash-bearing hemipelagites from the upper Shikoku Basin (600 to 800 mbfs) and the ash-free hemipelagites of the lower Shikoku basin sequences, down to the decollement (963 mbsf). The geometry of the tectonic features has been recorded in a local frame related to the core liner and then corrected to an absolute frame by the use of paleomagnetic measurements. The resulting geometry of homogeneous populations of slickenlined faults was used to estimate the reduced stress sensor. The main result is to show three consistent stress patterns. -from Authors