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Coast to coast study to yield North Island's deep secrets - 07/02/2001

Scientists from New Zealand, England, and Japan are to spend the next three weeks using a 400km-long line of earthquake recorders to find out more about the rock layers deep under the central North Island.

Seismograph map

About 300 portable seismographs will be placed at 1km intervals right across the North Island from Napier to Kawhia for the 20-day project. In terms of the amount of equipment and personnel, it is one of the largest scientific field projects in New Zealand.

As well as the on-land part of the project, scientists have placed 14 seismographs on the seafloor to the southeast of Napier. The most distant is 150km from shore and the nearest, 20km from Napier.

In scientific terms, the project is known as a seismic transect. It involves researchers and technicians from the Institute of Geological & Nuclear Sciences Limited (GNS), Victoria University of Wellington, Cambridge University UK, and Hokkaido University Japan.

The overseas organisations have supplied most of the equipment, including the highly specialised ocean bottom seismographs which were brought to New Zealand by Hokkaido University.

The instruments will record small acoustic signals set off by the scientists along the transect. At sea, the signals will be made by the research ship, Geco Resolution. From the signals recorded with the seismographs, scientists will build up a three-dimensional picture of rock structures and the tectonic plate boundary beneath the North Island and offshore to the east.

The Pacific plate, to the east of the North Island, is being forced under the Australian plate causing earthquakes and the volcanic activity of central North Island. Deformation of this tectonic boundary has also helped to produce the petroleum-bearing sedimentary basins to the west of the North Island.

" We have a limited knowledge of what is going on deep under the North Island," said project spokesman Fred Davey of the Institute of Geological & Nuclear Sciences Limited (GNS).

" This project will tell us about the properties of the rock layers forming the tectonic plates, and how these layers are being bent, fractured, pushed up, and forced down," Dr Davey said.

" Knowing more about these factors will lead to a better understanding of why and how earthquakes and volcanic activity occur in the North Island."

Additional recordings will be made with a line of instruments from Taupo to the Bay of Plenty coast. Information from this part of the project will help in understanding volcanism and deep geological structures in the central and northeastern volcanic region of the North Island.

At the end of February, when the project is scheduled to finish, all instruments will be retrieved.

The large amount of data from the project is expected to take months to compile before detailed analysis can start. Scientists expect it may take up to a year to produce initial findings.

Similar transects, also involving scientists from several countries, were undertaken across the South Island in 1996 and 1998. They provided an improved understanding of the geological processes occurring under the Southern Alps.

John Callan, Communications Co-ordinator, GNS