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Seafloor quake study off New Zealand to unlock tsunami mysteries

Source: Xinhua | May 12, 2014, Monday | Online Edition

AN international group of scientists have begun the biggest ever study of seafloor earthquakes in the ocean east of New Zealand's North Island, in a bid to better understand earthquake and tsunami threats around the world.

Thirty-two seismic monitoring devices, from the United States and Japan, would be set on the seafloor near Poverty Bay for one year recording slow-slip earthquakes and any upwards or downwards movement of the seafloor, New Zealand's Institute of Geological and Nuclear Sciences (GNS Science) announced today.

The deployments, part of a joint project involving New Zealand, Japan and the United States, would take place between 25 km and 100 km east of Gisborne in water depths ranging from 100 to 4,000 meters.

The project was designed to give valuable insights into the earthquake and tsunami potential of the Hikurangi subduction zone, where the Pacific tectonic plate is being thrust under or " subducted" beneath the Australian tectonic plate, in slow-slip quakes.

Occurring roughly every 18 month intervals in the area, slow- slip quakes involve large parts of the region moving eastward by up to two cm over one or two weeks.

If the movement occurred on land in seconds rather than weeks, like a normal earthquake, it would be equivalent to a magnitude 6 to 7 jolt, said a GNS Science statement.

The area was one of about a dozen worldwide where the events occurred regularly, but was unique in that they occurred at depths ranging from 5 km to 15 km under the seafloor.

In most other places in the world they occurred 20 km to 40 km under the surface.

The study would lead to a better appreciation of the earthquake and tsunami potential of this undersea fault system, GNS Science seismologist Bill Fry said in the statement

"Subduction zones, such as the one offshore the North Island, are responsible for generating the world's largest earthquakes, sometimes called megathrust quakes," Fry said.

"Recent examples are the magnitude 9 Tohoku quake in Japan in April 2011 and the magnitude 9.1 Sumatran quake in 2004."

Seismologists believed a megathrust quake of magnitude 9 was possible on the Hikurangi subduction zone.

"An earthquake of this size would produce damaging shaking throughout much of New Zealand plus a tsunami that would affect most of the country and potentially other parts of the Pacific as well," Fry said.

The instruments would provide accurate earthquake depths, which was important for revealing the three-dimensional distribution of earthquakes within the earth's crust.

The stored data would be downloaded and analyzed when they were retrieved from the seafloor in 2015.

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