Tuesday, November 10, 2015

Million-dollar fund to investigate earthquakes off Gisborne’s coast

An earthquake monitor

THE Government will put up more than a million dollars to fund a “rethink” of what we know about earthquakes off the Poverty Bay coast.

The Government-funded Marsden Fund, administered by the Royal Society of New Zealand, yesterday announced it would provide two GNS Science projects in this region with funding.

That will include a project that will test the hypothesis that seemingly harmless slow-slip earthquakes and surface deformation can change stresses in the earth’s crust, which increase the likelihood of mega earthquakes on the Hikurangi subduction zone.

The project, led by seismologist Bill Fry, has been awarded funding of $775,000 over the next three years.

Dr Fry said understanding changes on the subduction interface and their impact on neighbouring faults is key to more accurate earthquake forecasting in subduction regions

“The traditional model of the earthquake cycle, in which a locked fault slowly accumulates stress until it is too weak to resist failure, needs rethinking.

“Movement of subsurface fluids on and near faults is thought to be a key factor in changing the frictional strength of faults. But much is still unknown about the underlying physical processes involved.

“Understanding these changes on the subduction interface and their impact on neighbouring faults is key to more accurate earthquake forecasting in subduction regions.”

A key part of the project will be new, “extraordinarily rich” data recordings of two slow-slip earthquakes that occurred under the sea floor east of Gisborne late last year.

Ocean bottom seismometers

The two events were recorded by a network of about 35 ocean bottom seismometers, specifically deployed to record such events. Instruments were located about 50km off the Poverty Bay coast.

Dr Fry said had the slow-slip quakes occurred in seconds rather than over weeks, they would have each been equivalent to a magnitude 6.8 quake.

The data is regarded as the world’s best-ever recording of two successive slow-slip earthquakes in one region.

Using the data, Dr Fry and project co-leader Dr Stuart Henrys will apply newly-developed seismic methods to map stress and other physical properties across a cycle of slow-slip deformation in the offshore Poverty Bay region.

Another project, led by seismologist Yoshi Kaneko, will investigate how and why some parts of the Hikurangi subduction interface are firmly stuck and others slide past each other episodically.

It is a ‘fast-start’ project and has been awarded $300,000 over three years.

The project will use seismic tomography to image the three-dimensional structure near the plate interface in unprecedented detail to provide new information on its physical properties and find out what controls the spatial variation of megathrust slip behaviour.

GNS Science received funding for a further two projects in other parts of New Zealand. A GNS Science spokesman said the projects still had to be ‘officially contracted’, which could take a couple of months.

“The official start date is March 1, 2016. Even so, preparatory work is under way,” the spokesman said.

Because both projects here would rely on existing extensive data, there would be no need for new fieldwork.
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