A new method for calibrating marine biota living-depth using the 2016 Kaikōura Earthquake uplift

Abstract. The 2016 Mw 7.8 Kaikōura Earthquake (South Island, New Zealand) caused widespread complex ground deformation including significant coastal uplift of rocky shorelines. This coastal deformation is used here to develop a new methodology, in which intertidal marine biota have been calibrated against tide-gauge records to quantitatively constrain pre-deformation biota living depths relative to sea level. This living depth is then applied to biologically measured tectonic uplift at three other locations along the Kaikōura coast. We also test how tectonic uplift measured using this calibrated marine biota compares to vertical deformation measured, at the same localities, using instrumental methods [Light Detection and Ranging (LiDAR) and strong motion data], and non-calibrated biological methods. Data show that where biological data is collected by RTK-GNSS in sheltered locations, this new tide-gauge calibration method estimates tectonic uplift with an accuracy of ± ≤ 0.07 m in the vicinity of the tide-gauge, and an overall mean accuracy of ± 0.10 m or 10 % compared to differential LiDAR methods for all locations. Sites exposed to high wave wash, or data collected by tape-measure, are more likely to show higher uplift results. Tectonic uplift estimates derived using predictive tidal charts produce overall higher uplift estimates in comparison to tide-gauge calibrated and instrumental methods, with mean uplift results 0.21 m or 20 % higher than LiDAR results. This low-tech methodology can, however, produce uplift results that are broadly consistent with instrumental methodologies and might be applied with confidence in remote locations where satellite data or local tide-gauge measurements are not available.