Rollins C, Thingbaijam KKS, Hutchinson J, Gerstenberger MC, Christophersen A, Eberhart-Phillips D, Rastin SJ, Van Dissen RJ. 2022. An augmented New Zealand earthquake catalogue, event classifications, and models of the depth distribution of shallow earthquakes in the greater New Zealand region. Lower Hutt (NZ): GNS Science. 83 p. (GNS Science report; 2021/58). doi:10.21420/XT4Y-WY45.
Abstract
A serviceable seismic hazard model for New Zealand requires an earthquake catalogue with accurate and representative data about earthquake locations, depths, magnitudes and other parameters, as well as uncertainties on those data. Usable depth (and focal mechanism) data are particularly necessary in the Hikurangi and Puysegur subduction regions in order to distinguish whether earthquakes in those regions are in the upper plate, on the subduction interface or in the down-going slab, as these three regimes have very different hazard implications and must be modelled separately and accurately. Recent work has improved the event magnitudes in the New Zealand earthquake catalogue for use in the New Zealand National Seismic Hazard Model (NSHM) 2022; however, other parameters in the New Zealand catalogue remain of mixed quality, in particular, earthquake depths. Therefore, for use in several inputs to the NSHM 2022, we develop an augmented New Zealand earthquake catalogue in which we import higher-quality depths and depth uncertainties, focal mechanisms, and some locations and magnitudes from several relocated and global catalogues. Next, we use event depths, focal mechanisms, 3D models of the Hikurangi and Puysegur subduction interfaces and relative plate-motion directions to classify earthquakes as upper-plate, interface or intraslab, with special treatment of the remaining lower-quality event depths in the augmented catalogue. Finally, we produce models of the depth distribution of earthquakes in several sub-regions within the greater New Zealand region (including separate models for upper-plate, interface and intraslab earthquakes) for use within the Distributed Seismicity Model (DSM) component of the NSHM 2022. (The authors)
