Catalogue of 2001–2011 New Zealand earthquakes relocated with 3-D seismic velocity model and comparison to 2019–2020 auto-detected earthquakes in the sparsely instrumented southern South Island

Abstract

ABSTRACT Here we update a catalogue of 2001–2011 New Zealand earthquakes relocated with a 3-D seismic velocity model, which has recent improvements. We use P- and S-wave arrival times from earthquakes during 2001–2011 as these were manually picked with assigned quality. We demonstrate the usefulness of the catalogue by considering results from the southern South Island where GeoNet seismograph spacing is large. Later phase data used automatic picking and processing of arrival times. We relocate the 2019–2020 data from National Geohazards Monitoring Centre (NGMC) and compare seismicity patterns to consider its usefulness. We find that the auto-detected crustal earthquakes are more sparse in most of the southern South Island compared to the earlier analyst-picked data period, including Fiordland, which is one of the most seismically active areas in New Zealand. The auto-detected seismicity pattern is also problematic at greater depth and does not show a seismicity band in the lower crust across Southland evident in 2001–2011 data. The detection capability could be improved with a much denser permanent network. We recommend that the 2001–2011 relocated catalogues be used in studies of tectonics and seismic hazard across the South Island, and in studies that consider New Zealand wide seismicity patterns.