Seismic monitoring of the Auckland Volcanic Field during New Zealand's COVID-19 lock-down

Abstract. The city of Auckland, New Zealand (Tamaki Makaurau, Aotearoa) sits on top of an active volcanic field. Seismic stations in and around the city monitor activity of the Auckland Volcanic Field (AVF), and provide data to image its subsurface. The seismic sensors – some positioned at the surface and others in boreholes – are generally noisier during the day than the night. For most stations weekdays are noisier than weekends, proving human activity contributes to recordings of seismic noise, even on seismographs as deep as 384 m below the surface, and as far as 15 km from Auckland's Central Business District. Lock-down measures in New Zealand to battle the spread of COVID-19 allow us to separate sources of seismic energy and evaluate both the quality of the monitoring network, as well as the level of local seismicity. A matched-filtering scheme based on template matching with known earthquakes improved the existing catalogue of 5 known local earthquakes to 35 for the period between November 1st, 2019 and June 15th, 2020. However, the Level 4 lock-down from March 25th to April 27th – with its drop in anthropogenic seismic noise – did not mark an enhanced detection level. Nevertheless, it may be that wind and ocean swell mask the presence of weak local seismicity, particularly near surface-mounted seismographs in the Hauraki Gulf that show much higher levels of noise than the rest of the local network.