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Seismic survey of coastal fault

A series of controlled explosions next summer will allow scientists to complete a “brain scan” of New Zealand’s largest boundary fault, the Hikurangi subduction zone.

This is the second stage of a major research project that the Institute of Geological and Nuclear Science (GNS) is carrying out jointly with the National Institute of Water and Atmospheric Research (NIWA) and international agencies.

GNS and NIWA have received $6.47 million from the Ministry of Business, Innovation and Enterprise to support the research.

The Hikurangi subduction zone extends from Cook Strait to beyond East Cape.

The research is focused here because it is very shallow beneath the coast.

This makes it a globally-unique place to determine the shallow subduction process involved in earthquake and tsunami generation. The research covers several areas including paleo-seismic investigations at Pakarae and the installation of seismograph stations around the East Cape.

Also planned is an onshore seismic survey from the coast north of Gisborne to the Bay of Plenty over the 2018-19 summer. This will require drilling several approximately 50 metre-deep seismic shot holes, each of which will hold around 300 kilograms of explosives.

The findings will improve local earthquake simulation models.

In a presentation on the research to Gisborne District Council’s assets and infrastructure committee, Dr Stuart Henrys, from GNS, said the intention was to generate seismic waves from explosions.

The energy that bounced back from the layers in the earth could also be recorded on seismographs. This was the work they proposed to do in February.

Community consultation on this will begin in the coming weeks.

Subduction is where one tectonic plate dives or “subducts” beneath another.

Subduction zones cause the world’s largest earthquakes and generate devastating tsunami.

Researchers will investigate rock properties along the subduction interface to help determine what controls plate coupling and earthquake slip behaviour.

The information about Hikurangi margin earthquake sources will inform the pilot development of a real-time tsunami warning system.

Dr Henrys said they had a really good record of the earthquakes and would use that, plus the ship sound sources, to build a catscan image that was just like a brain scan.

What they did not have was the energy offshore and this was the experiment that they would do next summer.

Committee members commented that it sounded like a lot of explosives. He was asked if they could trigger an earthquake.

“I hope not.”

SHAKE IT, BABY: The Gisborne Choral Society and guests perform Shaky Places, a song cycle based on contemporary New Zealand poems, at St Andrew’s Church. File picture