Lidar and Luminescence Dating Analysis of Latest Pleistocene-Holocene Slip Rates on the Awatere fault at Saxton River, South Island, New Zealand

Abstract:

We use high-resolution lidar imagery and luminescence dating to constrain incremental Holocene–late Pleistocene slip rates at the well-known Saxton River site along the Awatere fault, which is a primary fault in the Marlborough Fault System, South Island, New Zealand. Previous studies examining the ages and displacements of offset fluvial terraces and bedrock features at the Saxton River site suggest that slip rates along the Awatere fault have been highly variable since ~16 ka, exhibiting rates as low as ~3 mm/yr and as fast ~13 mm/yr, with an average of ~6 mm/yr (e.g., Mason et al., 2006). Mapping on high-resolution lidar topographic data and additional field surveys yield revised measurements of the five fluvial terrace risers and bedrock ridge that have been offset by the Awatere fault at the Saxton River site. Improved dating of those geomorphic features provided by post-IR₅₀-IRSL₂₂₅ luminescence ages allows us to more accurately constrain the incremental slip rates recorded at this site. Preliminary results suggest that the slip rate during latest Pleistocene-Holocene time has indeed varied considerably over millennial timescales. This study is part of a broader effort aimed at determining incremental slip rates and paleo-earthquake ages and displacements from all four main Marlborough faults. Collectively, these data will allow us to determine how the Marlborough system faults have worked together during the Holocene-late Pleistocene to accommodate plate-boundary deformation in time and space.