Analysis of a New Marlborough Fault System Lidar Dataset: The Wairau and Hope faults, South Island, New Zealand

Abstract:

Newly acquired lidar digital topographic data acquired early 2014 from the four major faults of the Marlborough Fault System in northern South Island New Zealand allow measurement of fault offsets ~1 m to 100s of meters in unprecedented detail. The lidar dataset, acquired for us by the US National Center for Airborne Laser Mapping (NCALM) and New Zealand Aerial Mapping (NZAM), comprises 254 km of fault-parallel imagery in 1.2-to-1.5-km-wide swaths. These high-resolution data have an average shot density of ≥12 shots/m², and encompass the central Wairau, central and eastern Awatere, western and eastern Clarence, and eastern Hope fault segments. In this study, we focus on detailed measurements of small (3-25 m) and large (10s-100s of meters) geomorphic offsets at multiple sites along the central Wairau and eastern Hope faults. In addition to showing compilations of these offset observations, we present examples of the lidar data at several key study sites where offsets at multiple scales are discernable. The precise fault offsets we measure at these sites, combined with post-IR IRSL (225°C) single-grain K-feldspar dating of fluvial terrace sediments, will provide the basis for determining incremental slip rates on these faults at a range of latest Pleistocene to late Holocene timescales. 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.