US scientists head for the depths 

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A group of US scientists have begun the most comprehensive and expensive study of New Zealand's deep sea fault line ever attempted, equipped with a small army of state-of-the-art submersible seismographs.

With 30 of the devices, worth $150,000 each, on board their oceanographic research ship the Thomas G. Thompson, the crew are heading out of Christchurch on a serious science project. The robotic subs are dropped from the side of their vessel once in a series of particular locations, where they fall to the sea floor.

The earthquake data they gather will tell the scientists what is happening to New Zealand's fault lines, up to 500 kilometres out to sea.

The last time the fault line they are surveying fully "ruptured" was 300 years ago, but the scientists warn it will happen again - potentially in more than one region.

"Absolutely. It's inevitable, there's no doubting it," Professor Peter Molnar of the University of Colorado says. "In fact, to say 'The Big One' may be a mistake. The South Island will have its big one - the North Island, of course, can have a completely different big earthquake."

That means for seismologists,  there's no better place to study the movement of the tectonic plates over time.

Molnar says they can reconstruct the relative positions of the two sides of New Zealand, stretching back in time, better than seismologists can undertake similar studies anywhere else in the world.

But at around $6 million the science is neither cheap, nor quick.

Professor John Collins of the Woods Hole Oceanographic Institution says the team has spent seven or eight years trying to get the experiment funded.

Even getting reporters and cameramen on board the ship took a while. In these times of increased security, the ONE News crew had to be cleared through Washington.

The group of scientists will spend the next month analysing data from the seismographs, but it will be a year before they can tell exactly what is happening around New Zealand.

In the meantime, they sail with a friendly word of warning - be prepared for the next big quake.