PRELIMINARY ANALYSIS OF NEW MARLBOROUGH FAULT SYSTEM LIDAR DATASET: THE BRANCH RIVER SITE, WAIRAU FAULT, SOUTH ISLAND, NEW ZEALAND

Using newly acquired LiDAR digital topographic data, we measured offset river terraces and channels at the well-known Branch River site on the Wairau fault. We have also employed the post-IR IRSL (225°C) single-grain K-feldspar dating procedure to date offsets with the aim of generating multiple latest Pleistocene to mid-Holocene fault slip rates based on terrace offsets ranging from 25-60 m. In addition, detailed measurements of small (3-25 m) geomorphic offsets at multiple other sites along the fault provide information on displacements during the last few earthquakes on the Wairau fault. This is the first study in a series to explore a newly acquired LiDAR digital topographic dataset, collected in spring 2014, containing 254 km of fault-parallel imagery in 1.2- to 1.5-m-wide swaths along the four major faults of the Marlborough Fault System, South Island, New Zealand. These data have an average shot density of ≥14 shots/m², and encompass the western Wairau, central and eastern Awatere, western and eastern Clarence, and eastern Hope fault segments. This project is part of a broader effort to generate incremental slip rates and paleoearthquake ages from all four of the main faults that comprise the Marlborough Fault System with the goal of further understanding how mechanically complementary faults work together to accommodate relative plate motions.