6 May 2016

'Slow slips' could trigger big quakes

6:33 am on 6 May 2016

Scientists have discovered that slow-motion earthquakes known as 'slow slips' can trigger - or alleviate - large, tsunami-generating earthquakes.

Recording earthquake information

Recording earthquake information Photo: 123rf

One of the researchers, Laura Wallace of the University of Texas at Austin, said the team looked at a slow slip in September 2014 off the Gisborne coast, which took place over two weeks.

Dr Wallace said this slow slip happened along a plate boundary in the same place as a 7.2 earthquake in 1947, which generated a large tsunami near Gisborne.

She said if the slow slip's 15-20 cm of movement had occurred suddenly, rather over two weeks, it would have resulted in a magnitude 6.8 earthquake.

Slow slips occur frequently off the coast of New Zealand and involve slow movement along a faultline.

Dr Wallace stressed the findings contained good and bad news.

"Slow slip events relieve pressure on the plate boundary, they accommodate a lot of the plate motion," Dr Wallace said.

"But when they happen they redistribute stress to other parts of the plate boundary and can potentially trigger earthquakes."

Research had found a slow slip had occurred off the coast of Japan where a huge quake in 2009 triggered a disasterous tsunami.

"It is a double edged sword, these slow slip events, they can relieve stress and also cause stress," Dr Wallace said.

Studying the link between slow slips and earthquakes could eventually help in forecasting the likelihood of damaging earthquakes and tsunamis, she said.

That would fall short of predicting specific earthquakes, but could help forecast their probability.

The research - by scientists from New Zealand, the United States and Japan - was published in the latest issue of Science magazine.

Further research would be done in the area in 2018.

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