Dating coseismic marine terrace formation during the Kaikoura 2016 earthquake

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The recent earthquake in Kaikoura, New Zealand on 14th November 2016 resulted in the uplift of large stretches of coast. Previously intertidal rocky shore platforms cut into bedrock are now stranded high and dry above the tides. The opportunity to observe the marooning of raised marine terraces is rare, yet these are ubiquitous landforms flanking the coasts in tectonically active settings around the globe, from the edges of the Mediterranean Sea to the Pacific margin of the Andes and Rocky mountains. These marine terraces previously formed at sea level are important spatial and chronologic markers of the interactions between tectonic uplift and eustatic sea level change that allow reconstruction of a history of tectonic uplift rates. Terraces can be dated using cosmogenic isotopes (CIs), but the accuracy of ages is tied to inherent (and untested) assumptions about the nuclide inventory at the time of terrace abandonment. Moreover, their formation and abandonment are poorly understood because the processes involved are not typically observed in real time. The goal of this project is to address both of these existing knowledge gaps and use a shore platform instantaneously uplifted and abandoned during the 14th November 2016 Kaikoura, New Zealand earthquake to directly observe the processes of formation and abandonment of marine platforms. The Kaikoura earthquake demonstrated that the formation of stranded marine terraces can be due to instantaneous, coseismic uplift of previously active rocky shore platforms. We will measure 10Be concentrations from the surface of a newly stranded shore platform in a transect of in-situ bedrock samples so as to determine the apparent platform age at the time of terrace formation. We will also use measured 10Be concentrations in concert with existing data on shore platform and coastal erosion to understand the prior history of shore-platform development leading up to the earthquake in order to understand the inheritance of 10Be accumulated during active coastal development. The proposed work is vital for the provision of a baseline for future studies both locally and globally. Sampling must take place as soon as possible, prior to any significant breakdown of the surface due to subaerial weathering, deposition or human modification. This rare event provides a unique opportunity to calibrate and validate existing models for platform abandonment and evolution, and in turn improve our assessment of vertical tectonic rates and associated hazards in tectonically active coastal regions around the globe.