Roger, J.H.M.; Power, W.L.; Wang, X.; Burbidge, D.R.; Davison, A.; Ashraf, S.; Fensom, J.; Hanson, J.B. 2024 Tsunami monitoring with offshore DART systems: investigations regarding automatic triggers on the New Zealand DART NZA. GNS Science report 2024/39. 37 p.; doi: 10.21420/P9G0-3Y69
Abstract
In 2019, Aotearoa New Zealand started deploying a newly designed Deep-ocean Assessment and Reporting of Tsunami (DART) network comprising 12 oceanic bottom pressure recorders (BPRs) communicating to the National Geohazards Monitoring Centre (NGMC) by means of surface buoys equipped with satellite transmitters. A few months after its deployment, DART NZA, located ~2600 m deep offshore Cook Strait and the closest to New Zealand’s capital city Wellington, began intermittent automatic triggering due to unexpected signal variations of unknown origin. Over time, more and more of these NZA auto triggers occurred, each one requiring the duty officers, and subsequently the Tsunami Experts Panel (TEP) of New Zealand, to assess the potential hazard. Adjacent DART systems and coastal gauges were closely monitored for several hours following NZA auto triggers, but none showed any similar or related signals. To investigate the cause of the auto triggers at NZA, a series of hypotheses were developed for their origin, including system issue(s), internal waves, seismicity, underwater disturbances (e.g. turbidity currents, landslides), seafloor pockmark-related gas emissions, anthropogenic activities (e.g. large ships, geophysics exploration, etc.) and biologic activities (e.g. marine mammals, fishes, etc.). This report presents the data recorded by NZA, the different types of auto triggered signals observed and the investigations related to the different hypotheses. Finally, it proposes recommendations for further investigations (auths)
