ALBERT

Description: The New Zealand National Seismic Hazard Model (NSHM) was recently overhauled and revised in a three-year international effort. Of the many inputs into the NSHM, three of the most important ones are the total magnitude-frequency distribution (MFD) of earthquakes in the near-shore upper-plate region (e.g. the 2010-16 Canterbury and 2016 Kaikoura sequences), the MFD on the Hikurangi-Kermadec subduction zone, and the MFD on the Puysegur subduction zone (e.g. the 2009 Dusky Sound earthquake). To constrain these MFDs, we need good earthquake magnitudes, good event depths, and focal mechanisms (the latter two in order to distinguish whether earthquakes in the subduction regions are upper-plate, interface or intraslab). Recent work (Christophersen et al., 2022) has greatly improved the earthquake magnitudes in the New Zealand catalogue. Starting from their catalogue, we import higher-quality event depths, focal mechanisms, and 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. Then using this integrated catalogue, we estimate the MFD of earthquakes in the upper-plate region incorporating data back to 1843, balanced with the better data in the more recent catalogue. We estimate the MFDs on the Hikurangi–Kermadec and Puysegur subduction zones using a simplified approach with more recent data. Here, we will describe ongoing work in this area, including incorporating new earthquake data and describing earthquake clustering and rate uncertainty in less model-driven ways.