Natural Hazards 24: 267–284, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 267 Tsunami Hazard for the Auckland Region and Hauraki Gulf, New Zealand W. P. DE LANGEand T. R. HEALY Coastal Marine Group, Department of Earth Sciences, The University of Waikato, Private Bag 3105, Hamilton, New Zealand (Accepted: 31 May 2000) Abstract. The Hauraki Gulf is a semi-enclosed sea next to the largest population centre in New Zealand, the Auckland metropolitan region. The potential tsunami hazard is of concern to regional and local planners around the Hauraki Gulf. The Hauraki Gulf has recorded 11 tsunamis and one meteorological tsunami (rissaga) since 1840. The historical tsunami data are relatively sparse, particularly for the largest events in 1868 and 1883. Moreover, local sources may produce damaging tsunamis but none has occurred during recorded history. Therefore numerical modelling of potential tsunami events provides a powerful tool to obtain data for planning purposes. Three main scenarios have been identified for numerical modelling: 1. A teletsunami event from an earthquake off the West Coast of South America. Historically this region has produced the largest teletsunamis in the Hauraki Gulf. 2. A tsunami generated by a local earthquake along the Kerepehi Fault. This fault bisects the Gulf, has been active during the last century at the southern inland end, and is overlain by a considerable thickness of soft sediment that may amplify the seismic waves. 3. A tsunami generated by a volcanic eruption within the Auckland Volcanic Field. This field has involved a series of mainly monogenetic basaltic eruptions over the last 140,000 years. Many of these eruptions have involved phreatomagmatic eruptions around the coastal margins, or within the shallow waters close to Auckland. Key words: Auckland region, teletsunami, Kerepehi Fault, tsunami hazards and impacts 1. Introduction The metropolitan region of Auckland is the largest in New Zealand, with more than one million inhabitants. Auckland occupies the area surrounding the narrow isthmus between the Hauraki Gulf and Manakau Harbour, giving the region a mari- time focus (Figure 1). Not surprisingly there is considerable infrastructure located close to the sea, including New Zealand’s largest general cargo port, several major marinas, and recreational beaches and facilities. Since the last significant tsunami in 1964, there has been considerable invest- ment in coastal infrastructure including marinas, tourist attractions and upgraded port facilities. This is likely to continue with the upcoming Americas Cup Regatta of 2002. Therefore the Auckland Regional Council has initiated a Lifelines Project