Abstract
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 the upper living limits of intertidal marine biota have been calibrated against tide-gauge records to quantitatively constrain pre-deformation biota living position relative to sea level. This living position is then applied to measure coseismic uplift at three other locations along the Kaikōura coast. We then assess how coseismic uplift derived using this calibrated biological method compares to that measured using other methods, such as light detection and ranging (lidar) and strong-motion data, as well as non-calibrated biological methods at the same localities. The results show that where biological data are collected by a real-time kinematic (RTK) global navigation satellite system (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 may be applied with confidence in remote locations where lidar or local tide-gauge measurements are not available.
Highlights
IntroductionVertical displacement has been measured globally using intertidal marine biota on rocky coastlines, which often provide important constraints for incremental uplift during large-magnitude earthquakes and cumulative geological uplift (e.g. Alaska: Plafker, 1965; California: Carver et al, 1994; Mexico: Bodin and Klinger, 1986; Ramirez-Herrera and Orozco, 2002; Costa Rica: Plafker and Ward, 1992; Chile: Fitzroy, 1839; Castilla, 1988; Castilla et al, 2010; Farías, 2010; Vargas et al, 2011; Melnick et al, 2012; Argentina: Ortlieb et al, 1996; eastern Mediterranean: Pirazzoli et al, 1982; Stiros et al, 1992; Laborel and LaborelDugeun, 1994; Mouslopoulou et al, 2015a; Japan: Pirazzoli et al, 1985; New Zealand: Mouslopoulou et al, 2019)
Tectonic deformation determined from uplifted intertidal biozone indicators produces results comparable with tectonic uplift recorded by the Kaikoura tide gauge, remote sensing datasets and strong-motion seismic data
Calibrating measured intertidal biological data to real-time tide-gauge records gives results within an average of 0.11 m of those derived from direct uplift of the tide gauge and localised differential lidar values
Summary
Vertical displacement has been measured globally using intertidal marine biota on rocky coastlines, which often provide important constraints for incremental uplift during large-magnitude earthquakes and cumulative geological uplift (e.g. Alaska: Plafker, 1965; California: Carver et al, 1994; Mexico: Bodin and Klinger, 1986; Ramirez-Herrera and Orozco, 2002; Costa Rica: Plafker and Ward, 1992; Chile: Fitzroy, 1839; Castilla, 1988; Castilla et al, 2010; Farías, 2010; Vargas et al, 2011; Melnick et al, 2012; Argentina: Ortlieb et al, 1996; eastern Mediterranean: Pirazzoli et al, 1982; Stiros et al, 1992; Laborel and LaborelDugeun, 1994; Mouslopoulou et al, 2015a; Japan: Pirazzoli et al, 1985; New Zealand: Mouslopoulou et al, 2019). Biological data were the basis for the first written records of coastal uplift following earthquakes along the Chilean coast (Graham, 1824; Fitzroy, 1839; Wesson, 2017) and continue to provide important constraints for elastic rebound and coseismic slip processes together with the locations, depth and dip of causal faults Quantifying earthquake uplift from such biological datasets has been achieved using a variety of techniques from simple measuring devices, such as tape measures, to laser survey methods and global navigation satellite system (GNSS) techniques. Melnick et al, 2012; Jaramillo et al, 2017) have successfully compared the reliability of the conventionally acquired biological uplift records against real-time kinematic (RTK) global navigation satellite system (GNSS) measurements, none have attempted to numerically and independently quantify the living position of each biological marker. None of the above studies have systematically compared the manually collected tape-measure estimates of coseismic uplift with instrumental earthquake uplift datasets at individual localities to quantitatively assess the potential uncertainty inherent in the various techniques
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