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Slow-motion quake helps seismic science

NZ NewswireNZ Newswire 5/05/2016

Traditional and "slow-motion" earthquakes can occur on the same fault, scientists have discovered, after a world-first study of a two-week event off the New Zealand coast.

So-called "slow-slip events" are similar to normal earthquakes in that they relieve pressure of tectonic plate movements, but they do so over days to weeks rather than in sudden thrusts.

Now scientists have discovered they can do similar damage to the shallow portion of a fault as normal earthquakes following an investigation of an event at the Hikurangi subduction zone.

It also helps geophysicists further understand the relationship between the types of earthquakes by acknowledging both can occur on the same part of the fault.

"The link has been difficult to document in the past because most slow-slip monitoring networks are strictly land-based and are located far from the offshore trenches," project leader Laura Wallace said.

The international team from New Zealand, Japan and the United States studied the two-week slow-slip event at Hikurangi when it occurred in 2014 and published their findings in Science on Friday.

If the amount of pressure released at Hikurangi during the slow-motion event was released at once, it would have been the equivalent of a magnitude 6.8 earthquake.

GNS Science geophysicist Dr Stuart Henrys, who helped author the paper, said their discovery has changed the traditional understanding of how earthquakes are forecast.

"We now know that faults don't behave that way and non-traditional earthquakes (like slow-slip) occur throughout the earthquake cycle," he said.

"Understanding and monitoring the time changes of this system may provide a valuable tool to forecast future damaging earthquakes."

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