On-going 'slow-slip' earthquakes in New Zealand

This may be of interest in view of the present quakes in central NZ

Massive New Zealand Earthquake Has Been Going On All Year

Inquistr,

27 May, 2013

A massive earthquake is going on under Wellington, New Zealand. But daily life continues in the town with none of the locals hiding out under desks or inside doorways until the tremors pass.

This is because, while the quake measures an impressive 7 on the Richter scale, even sensitive recording instruments can barely register the shaking. GeoNet Operations Scientist Caroline Little explained:

“This is because, unlike a normal earthquake, these plate movements happen very slowly in a process known as ‘slow-slip events.’ This Kapiti slow-slip event is affecting an area spanning over 100 km from Levin to the Marlborough Islands.”

A conventional earthquake happens when one side of a fault line suddenly shifts past the other. While a slow-slip event is similar, it takes much longer for the fault to move and release its pent-up energy. Because of this, Little added, “slow-slip events are often called ‘silent earthquakes.’ ”

The New Zealand earthquake started in January and will likely continue on for several months. GeoNet’s GPS instruments have been placed in Wellington and Kapiti to monitor the quake’s movement. So far, they have shown that the Pacific and Australian tectonic plates are slipping past each other more rapidly than they have in the past.

Slow-slip events are a relatively common occurrence at subduction zones around the world, including four in New Zealand alone. Kapati, Manawatu, Hawke’s Bay, and Gisborne have all seen impressive earthquakes. Subduction is a process where one tectonic plate is diving underneath another.

Kapiti and Manawaty typically produce deep slow-slip events that last for months to a year. They tend to recur every five years. But Hawke’s Bay and Gisborne see shallower events that last only a few weeks. They happen every one to two years.

There will be no noticeable impact from the massive New Zealand earthquake though the country will move a few centimeters away from Australia.