Collaborative Research: Tracing the Geomorphic Signature of Strike-Slip Faulting in Marlborough Hill Country, South Island, New Zealand

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When active, strike-slip faults are among the most dangerous geologic features on Earth. At present, characterizing in detail their slip rates, seismic hazard, and evolution over a range of timescales challenges the earth science community. An under-exploited tool in strike-slip fault characterization is quantitative analysis of the geomorphic response to lateral fault motion to extract tectonic information directly from the landscape. At present, studies of this nature typically focus solely on vertical motion in mountain systems. This research will develop a new framework for applying geomorphic analysis to strike-slip fault systems and in doing so, will move the scientific community toward a more comprehensive and quantitative understanding of the geomorphic response to lateral crustal motion, which we currently lack. A suite of parallel right-lateral strike-slip faults known as the Marlborough Fault System (MFS), South Island, New Zealand offers an excellent natural laboratory for this problem. From north to south, fault initiation ages as well as cumulative fault displacement are thought to decrease whereas slip rates increase over four fold, providing snapshots of different stages of fault evolution. Using the MFS as a natural experiment, this project will test the degree to which surface processes and landforms can be used as a quantitative indicator of lateral fault activity. Geomorphology, thermochronology, and numerical modeling will be applied to document regional erosion history, identify differences (or similarities) in landscape morphology between regions of variable slip rate, fault age, and degree of vertical motion, and make quantitative predictions about the surficial response to different strike-slip fault scenarios using landscape evolution models.The primary goal of this work is to test the degree to which landscape response can be used as an indicator of strike-slip fault activity. Studying the landscape response to strike-slip faulting within the Marlborough Fault System has the potential to improve our understanding of horizontal fault zone activity and the geomorphic response to fault motion, at this location and in general; ultimately mitigating the hazards associated with living in and around strike-slip faults. Seismic activity occurs frequently within the greater Marlborough region, including along faults that were previously unknown (as in the case of the destructive Darfield 2010 magnitude 7.1 and Christchurch 2011 magnitude 6.3 earthquakes). Results from this work will benefit seismic hazard assessment at this location, as well as at many other locations around the world where far less is known about active strike-slip faulting. Detailed study of the timing and magnitude of vertical motion along the primary fault strands as well as along the secondary contractional structures within the MFS will also provide new constraints on the tectonic evolution of the New Zealand orogen and foster already strong international collaboration between U.S. and New Zealand geologists.