Using the Seismic Quiet in Auckland, New Zealand, to evaluate its seismic monitoring network and search for local seismicity

Abstract:

The city of Auckland, New Zealand (Tamaki Makaurau, Aotearoa) sits on top of an Active Volcanic Field. The seismic stations that monitor the Auckland Volcanic Field (AVF), positioned at the surface or in a borehole, are noisier during the days than the nights. Furthermore, weekdays are noisier than weekends, suggesting human activity contributes to recordings of seismic noise, even on seismographs 380m below the city and as far as 15 kilometers from downtown Auckland. Lockdown measures in New Zealand to battle the spread of COVID-19 help us separate sources of seismic energy and evaluate both the quality of the monitoring network, as well as the level of local seismicity. A month-long reduction in anthropogenic seismic noise confirms the a-seismic nature of the AVF, even though wind and waves continued to obscure weak seismicity, particularly near some of the surface-mounted seismographs in the network.