Quakes have a silver lining for earthquake scientists

29 August 2013

Quakes have a silver lining for earthquake scientists

The numerous aftershocks from the recent Cook Strait earthquakes might be unsettling for many but they are proving to be useful for a team of earthquake scientists researching seismic activity in New Zealand.

Previously, the researchers from Victoria University and GNS Science have simulated earthquakes by detonating explosions in 50-metre deep boreholes on the Kapiti Coast and in the Wairarapa.

The exercise is part of a project to learn more about the potential for megathrust earthquakes, quakes of magnitude 9 or larger which occur at plate boundaries.

Between 2009 and 2011, the scientists recorded the echo created by the explosions underground to help build two dimensional and three dimensional images of rock structures and the plate boundary beneath the lower North Island.

But thanks to the recent swarm of shakes, the team is now able to supplement this data with information from real earthquakes, says Professor Martha Savage from Victoria’s Institute of Geophyiscs, School of Geography, Environment and Earth Sciences.

The researchers will be gathering data from seven seismometers recently installed by GNS Science in the northern South Island, and an additional 21 seismometers to be located in a 250 kilometre line extending from Molesworth Station, at the top of the South Island, up through Levin.

These will measure ground movement during earthquakes and enable scientists to map the interior of the Earth and locate and measure the size of an earthquake.

“This latest lot of equipment will be out for several months to take advantage of the numerous shakes that we expect to continue in the south in the 60 day period following the recent significant earthquakes.

“We are also expecting that the normal background earthquake activity, in which small quakes occur most weeks, will continue further north.”

Professor Savage says the results will help scientists examine the ‘subduction interface’, or boundary along which the Pacific plate is being pushed underneath New Zealand on the Australian plate.

Sudden slipping on subduction interfaces is what causes the largest, most damaging earthquakes, such as the 2004 Boxing Day earthquake in Sumatara and the 2011 Tohoku earthquake in Japan.

The current work complements the earlier research, which gave the team an extremely high resolution image of the subduction interface.

“The latest study will give us data about the material that sits at the interface of the plates after an earthquake. We’re interested in finding out, for example, if the material slips easily or whether it locks up,” says Professor Savage.

She says materials that slip easily can sometimes relieve the tectonic stress caused by plates grinding together and result in earthquakes that are less hazardous.

“Overall, it will give Wellingtonians more information about the risks posed by earthquakes and just how prepared we need to be.”

The study, which is part of a wider project involving scientists at GNS Science, the Earthquake Research Institute at the University of Tokyo, the Disaster Prevention Research Institute at Kyoto University, University of Nevada, Reno, and the University of Southern California, will continue until January 2014.
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