NZ 10 tsunami alarm stations short

New Zealand is short of about 10 seismograph stations which would give the country better warning of an approaching tsunami.

Geonet, the national monitoring system, has gone from just four stations in 2001 to 36 now - a vast improvement, say scientists.

But the network still has holes in its coverage of Auckland City, Whangarei, the Bay of Plenty, Taranaki, Marlborough, the East Coast of the North Island and the West Coast of the South Island.

GeoNet director Dr Hugh Cowan said the lack of coverage in these areas could lead to spurious results and false alarms.

However, it would not miss the kind of earthquake which triggered the Boxing Day tsunami across Asia.

"Anything capable of generating a tsunami, that's going to boom in loud and clear from hundreds of kilometres away. The Sumatra earthquake went on for several minutes."

In the past fortnight, two earthquakes have occurred west of Auckland Island in the Tasman Sea.

An 8.1 magnitude quake was felt over a large part of the lower South Island on December 23 and a 6.1 quake occurred on Tuesday.

Geonet seismologist Brian Ferris said there was no cause for alarm. New Zealand had experienced a low level of activity in the past 12 months.

GeoNet, which is part of the Institute of Geological and Nuclear Science (GNS), is three years into a 10-year upgrade, but has only two-thirds of the funding recommended in the $80 million 2001 proposal.

Dr Cowan said the partial funding meant fewer seismograph stations and resources to analyse data. While the present system was a "strong backbone", more funds would be needed "to achieve the full promise of what was originally proposed".

The Earthquake Commission had pledged $5 million a year for 10 years, but money from other sources had been minimal. As a result, GeoNet had to reconfigure the network.

Commission general manager David Middleton said it had been lobbying local and regional councils to financially support GeoNet. With a few exceptions, these sectors had been unable to contribute.

He was optimistic the commission would be able to find more money at its board meeting next month so the network could be completed.

The activity between the Australian and Pacific plates made New Zealand vulnerable to local tsunami as well as distant tsunami from South America or Antarctica, said Mr Middleton.

GeoNet monitors seismic activity that could lead to local tsunami.

The Pacific Tsunami Warning Centre in Hawaii monitors activity outside the range of GeoNet's network. For tsunamis off the coast of South America, it can provide 12 to 14 hours' warning.

Both networks have direct communication lines to the Civil Defence Ministry. If a warning or evacuation is necessary, national officers inform local civil defence organisations, emergency services and councils.

Readiness manager Mike O'Leary said the aim was to inform people so they could be responsible for their own evacuation.