Structural and morpho-tectonic evidence of Quaternary faulting within the Moutere Depression, South Island, New Zealand

The subsurface structure of the Moutere Depression is obscured by a thick Plio-Quaternary gravel sequence. Surface and subsurface data have been used to define a blind basement pop-up bounded to the west by a NNE-striking reverse fault dipping c. 50°E (Ruby Bay-Moutere Fault, RB-MF). The RB-MF is geometrically and kinematically similar to the adjacent Waimea-Flaxmore Fault System (W-FFS) and linked to the Surville Fault offshore and the Tutaki Fault to the south. Reverse-slip activity on the RB-MF started post 21–18 Ma and continued after deposition of the lower Pleistocene gravel sequence, but the fault tip remains buried. Persistent Quaternary activity with progressive development of a hanging wall anticline is inferred from surface topography and deformation of late Quaternary river terraces. The collected evidence suggests that the RB-MF is capable of being reactivated in the present-day stress field, though slip rates are lower than those of the Holocene-active W-FFS.