The paleotsunami record of the Auckland region and implications for understanding tsunami hazards

ABSTRACT

The Auckland region does not have a historic record of significant tsunamis but modelling suggests the eastern coastline could be exposed to tsunamis from the Kermadec Trench with wave amplitudes of up to 10 m on Great Barrier Island/Aotea and 1–5 m on the mainland. Paleotsunami research could contribute to filling the disconnect between historic records and tsunami modelling by providing a tsunami record over a time span of thousands of years that is more likely to capture the long recurrence intervals of great subduction earthquakes at the Kermadec Trench. Here we review existing paleotsunami information and results of new field studies in the Auckland region (primarily on Great Barrier Island/Aotea). Three sites (Tāwharanui, Whangapoua Beach and Harataonga Bay) have strong evidence of Holocene paleotsunami but the dating of the inferred paleotsunamis at all sites is relatively poor. The coastline of Auckland and its neighbouring regions offer our most promising sites to better understand the size and frequency of large to great Kermadec Trench earthquakes and this information could be of critical importance for understanding tsunami risk in New Zealand.

KEYWORDS:

• Tsunami
• tsunami hazard
• Auckland
• Great Barrier Island/Aotea
• Kermadec trench

Acknowledgements

We thank William Power for the provision of tsunami models and advice on site selection. We also thank the Department of Conservation for the research permit for undertaking work on Great Barrier Island/Aotea. Bruce Hayward helped with all field work and particularly improved our understanding of the Whangapoua Beach gravel sheet. Lorna Strachan (University of Auckland) and James Goff (University of New South Wales) contributed to initial discussions about this project and helped with site selection. Multiple landowners on Great Barrier Island/Aotea and at Pakiri are also thanked for allowing access to their land. Jenny Dahl helped with radiocarbon sample selection. An early version of this manuscript was reviewed by Kristie-Lee Thomas and Jean Roger, and this version of the manuscript was reviewed by Andy Howell,William Power, Emily Lane and one anonymous reviewer, we thank them for their insightful reviews.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Additional data that supports this manuscript (such as core locations coordinates and detailed stratigraphic logs) are in the GNS Science Report of Clark et al. (2020) available at https://shop.gns.cri.nz/sr_2020-34-pdf/

Additional information

Funding

Funding for this study was provided by the Earthquake Commission (Project 16/729) and it was supported by the GNS Science Hazard and Risk Management SSIF Programme (funded by the Ministry of Business, Innovation and Employment).