Power, W.L.; Burbidge, D.R.; Gusman, A.R. 2022 The 2021 update to New Zealand’s National Tsunami Hazard Model. Lower Hutt, N.Z.: GNS Science. GNS Science report 2022/06. 63 p.; doi: 10.21420/X2XQ-HT52
Abstract
The National Tsunami Hazard Model (NTHM) provides estimates of tsunami heights at the shoreline for return periods of up to 2500 years. It is used as a basis for selecting scenarios used for tsunami inundation modelling, which underpins tsunami evacuation zone design, land use planning and risk assessments. The original NTHM was completed in 2013, though it built upon a 2005 study focused only on the main coastal cities. Since 2013, there have been improvements in the understanding of tsunami sources and in the techniques of tsunami modelling, and this report describes an incremental update incorporating those improvements. This new revision we refer to as the 2021 NTHM. One area of improvement is in the definition of earthquake recurrences, and the update uses parameters from the Global Earthquake Model (GEM), which was still in development at the time of the 2013 NTHM.The 2021 NTHM makes use of a broad catalogue of simulated tsunami events caused by subduction earthquakes from around the Pacific. This catalogue was developed in 2019, initially for the purpose of informing real-time tsunami forecasts. By using this large catalogue of scenarios, and through more sophisticated use of scaling relationships, it is expected that the 2021 NTHM should produce more accurate tsunami hazard estimates. Modelling of tsunami caused by crustal faults close to New Zealand has also been significantly improved. The 2013 NTHM used simple empirical relationships to estimate tsunami heights, and here those have been replaced by using scaled hydrodynamic models, which should produce significantly more accurate results. Overall, we find that the 2021 NTHM tends to produce similar or slightly lower estimates of tsunami hazard at the shoreline compared to the 2013 NTHM at most locations and return times. The main exception to this is the east coast of the North Island, for which some areas are estimated to have higher hazard at longer return times. We anticipate that the introduction of improved tsunami height estimates will lead to better choices of scenarios for inundation modelling studies. (auth)
