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World’s shallowest slow motion earthquakes detected off the North Island's east coast

4 years ago by Laura Wallace


An international team of researchers from the US, Japan and New Zealand have found that slow-motion earthquakes or “slow slip events” can rupture the shallow portion of a fault that also moves in large, tsunami-generating earthquakes. This finding increases our understanding of the relationship between slow slip and normal earthquakes by showing that the two types of events can occur on the same part of a plate boundary. 

This research was carried out using a network of highly-sensitive seafloor pressure recorders. In September 2014, the team detected a slow slip event off the Gisborne coast beneath the seafloor. This event lasted two weeks, resulting in 15-20 centimeters of movement along the "Hikurangi megathrust” that forms the plate boundary between the North Island and the Pacific Plate. If the movement had occurred suddenly, rather than slowly over two weeks, it would have resulted in a magnitude 6.8 earthquake. 

Slow slip events are similar to earthquakes, but instead of releasing strain between two tectonic plates in seconds, they do it over days to weeks, creating quiet, centimeter-sized shifts in the landscape. In a few cases, these small shifts have been associated with setting off destructive earthquakes, such as the magnitude 9.0 Tohoku-Oki earthquake that occurred off the coast of Japan in 2011 and generated a tsunami which caused the Fukushima Daiichi nuclear power plant disaster.

Dr Wallace said the linkage between slow slip events and earthquakes could eventually help in forecasting the likelihood of damaging earthquakes. “To do that we will have to understand the links between slow slip events and earthquakes much better than we currently do,” she said.

This research has just been published in the latest issue of Science -