Signals from the Deep – Triggers Observed on the New Zealand Deep-ocean and Reporting on Tsunamis (DART) Network
Presentation
Authors: Megan Madley, Jean Roger, Jonathan B. Hanson, David Burbidge, William Power, Aditya Gusman, Xiaoming Wang
Event: Geosciences NZ Conference, 29 Nov - 01 Dec 2022, Palmerston North, NZ
Summary: This presentation was on the COMCOT tsunami simulation model and its features and recent developments, including modelling capabilities of volcanic source tsunamis such as by air pressure waves and mass failures.
Xiaoming Wang
Project Leader: Simulate & Tsunami Scientist
In 2019, New Zealand implemented a deep ocean network to monitor changes in sea level around its shores and the Southwestern Pacific Ocean. This is a collaborative effort between multiple scientific institutes and government agencies. The array consists of 12 DART tsunameters which focus on monitoring tsunamis from the Hikurangi, Kermadec, Tonga, and Vanuatu subduction zones. Regular, 15 minute, water pressure observations are reported by the DART sea floor pressure recorders which infer the sea-level height above the pressure recorder. Any abnormal fluctuations in sea-level which matches certain criteria causes the instrument to ‘trigger’. When in triggered/response mode the sampling period reported back to GNS Science decreases to 15 seconds. This signal is known as an auto-trigger. When a DART is auto-triggered, the National Geohazard Monitoring Centre (NGMC), along with the Tsunami Experts Panel (TEP), if activated, assess the potential threat to New Zealand, evaluating if the auto-trigger is linked to any tsunami waves that could threaten the coast of New Zealand.
We have generated an auto-trigger catalogue to assess signals as they come in and to avoid numerous parasitic activations that could be related to non-tsunami waves like sensor offset, internal waves, seismic shaking, atmospheric pressure jumps, etc. This catalogue will allow the NGMC and GNS responders to quickly assess auto-triggers and then decide if the TEP or further activations are required. This catalogue currently consists of six different auto-trigger categories: Earthquakes, Tsunamis, Positive and Negative Spikes, Subsidence/Offset and Multiple Spikes. These categories are evolving as we develop a better understanding on their origins (instrumental, natural phenomenon or human induced). A few examples of these auto-trigger events will be presented including the February 2021 Loyalty Islands event, the triplet earthquake events in March 2021, signals seen at NZA of unknown origin, and the January 2022 Hunga Tonga-Hunga Ha’apai event.