More of NZ's coastline exposed to tsunami hazard

New tsunami risk calculations for NZ don't make for confident reading. Photo / Warren Buckland

A large tsunami generated very close to the coast of New Zealand would arrive before warning sirens could be activated, a new report has found.

Scientists are warning that anyone close to the coast who feels a strong earthquake which makes it hard to stand up or a small but long earthquake to get to high ground immediately.

The Ministry for Civil Defence and Emergency Management's Review of Tsunami Hazard in New Zealand, released today, is an update of a report on tsunami hazards done in 2005.

It's meant to reinforce the need for the public to understand and be prepared to respond to the threat of a tsunami.

It found that parts of our coast were exposed to a greater tsunami hazard than previously thought, while the hazard in other coastal regions was the same or less.

The main areas where tsunamis were a greater risk than previously understood included the coasts of Northland, the north-east and north-west part of the Auckland region and Great Barrier Island, along with the coasts of Northland, the Coromandel Peninsula, the Bay of Plenty the East Cape of the North Island and parts of the Wairarapa coast, Southland, Stewart Island, Fiordland and Westland.

Civil Defence said this year's report incorporated new research and "significant changes in scientific understanding'' since the 2005 report.

"It focuses on the entire New Zealand coastline rather than just the main population centres. It also uses more advanced modelling to quantify the tsunami hazard. Areas where the hazard is higher are the North Island's east-facing coasts and the southwest of the South Island. In other coastal regions, the tsunami hazard remains about the same, or has even decreased.

"Our recent research and modelling has shown the hazard from near-source tsunami with little travel time is higher than previously estimated. This is particularly the case for tsunami generated by undersea earthquakes off the North Island's east coast.''

The 220-page report also found New Zealand had experienced about 10 tsunami of 5 metres or more since 1840 and that dangerous local and regional tsunami - those that take fewer than three hours to reach here - may occur in New Zealand about every 40 to 50 years on average.

"So it is likely that at least one will occur in the lifetime of most New Zealanders.''

Resulting from the review, the ministry said it would be emphasising the existing public messages about tsunami and encouraging councils and the 16 regional Civil Defence groups to reinforce the national public messages with more specific local and regional information. The ministry would also hold regional seminars next month and in November.