Geological drilling off NZ supported

Virginia Toy
Virginia Toy
Geological drilling should be undertaken near New Zealand to check for key new tsunami risk factors recently discovered by scientists investigating Japan's devastating tsunami, geologist Dr Virginia Toy says.

Dr Toy, a lecturer in the University of Otago geology department, was part of a team of 27 scientists from 10 countries who last year recovered deep core samples by drilling into a key fault off the Japanese coast.

In April last year, the International Ocean Discovery Programme research vessel Chikyu, with Dr Toy aboard, drilled to about 7740m below sea level and about 850m into underlying rock in a deep-sea trench area, about 6910m deep, off the Japanese east coast.

The record-setting drilling had aimed to explain why huge rock movements - of up to 50m - recently took place in a subduction zone near Japan.

These movements triggered the massive Fukushima tsunami, which killed more than 20,000 people, in March 2011.

The researchers on this expedition, known as the Japan Trench Fast Drilling Project, have since produced three papers, published in the journal Science.

Research from Otago University, and from the team of international scientists showed for the first time that fine sediment clay within the Japan Trench plate boundary megathrust fault was a key factor in triggering the devastating tsunami in 2011.

In the fault, a special type of clay, called smectite, had acted as ''an incredibly slippery lubricant'', allowing the huge quake to occur.

A proposal had already been made by other researchers to have the same research vessel, Chikyu, undertake research at the Hikurangi Trench, about 100km off the east coast of the North Island, to determine the composition of its rocks.

If the subduction megathrust faults in that area had similar composition and fabric to the Japanese area tested, they could potentially ''generate large tsunami when they do fail in future earthquakes,'' Dr Toy warned.

It was in New Zealand's interests to check the Hikurangi Trench area to understand the currently unknown composition of the underlying rocks and if they posed higher-than-expected tsunami risks to the North Island, she said.

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