Earthquake Rate Variability in the Auckland Volcanic Field Within a Long‐Duration Self‐Consistent Earthquake Catalogue

Eruptions in the Auckland Volcanic Field in Aotearoa New Zealand have not occurred since seismic monitoring began in Aotearoa New Zealand, but it is generally presumed that future eruptions from the Auckland Volcanic Field will be preceded by elevated rates of seismicity. High levels of anthropogenic seismic noise, generally low numbers of earthquakes and relatively high earthquake detection thresholds used for nationwide earthquake monitoring by the Aotearoa New Zealand national earthquake monitoring system (GeoNet) mean that the national earthquake catalogue used for volcanic monitoring contains few earthquakes in the Auckland Volcanic Field. Moreover, variations in cataloguing methods throughout the history of seismic monitoring mean that the quality and completeness of the GeoNet earthquake catalogue in Auckland are strongly heterogeneous in time precluding robust analysis of earthquake occurrence variability within the Auckland Volcanic Field and hence inhibit the identification of possible precursory changes from that background state. We apply a semi‐automated workflow, incorporating modern machine‐learning earthquake detection methods validated by manual review, to develop a self‐consistent catalogue of seismicity in the Auckland Volcanic Field spanning 2011–2022 which we use to evaluate the background state of seismicity within the Auckland Volcanic Field in a time of quiescence. This catalogue contains 328 earthquakes within the Auckland Volcanic Field monitoring region, more than five times as many earthquakes as catalogued by GeoNet. The new catalogue is composed mostly of background seismicity with some discrete clusters. We confirm that the background rate of seismicity in Auckland is low (approximately 21 earthquakes annually above magnitude 0.6: the magnitude of completeness of this new catalogue) and provide a statistically useful indication of that background state, both in time and space, from which to characterise possible deviations prior to a future eruption within the Auckland Volcanic Field.