Slow-slip quake 'hits' Wellington

20:06, May 27 2013
Kapiti slow slip earthquake
Kapiti slow-slip 2013

What would be Wellington's biggest earthquake in 150 years is happening right now - not that you'll feel the jolt.

The magnitude-7 equivalent quake, 40km deep, is an event, when the movement of tectonic plates occurs over hours to months rather than seconds.

GeoNet scientists said even their precision instruments were picking very little up from the 100km area of Levin to the Marlborough Sounds, along the plate boundary.

Almost imperceptibly, the Pacific and Australian plates had been slipping past each other since January and would continue for up to a year, GeoNet scientist Caroline Little said.

“We don’t see anything at the surface.”

Apart from moving a few centimetres further away from Australia, there would be no noticeable impact from this seismic movement.

But slow-slip quakes had an undetermined relationship with large earthquakes, which were accompanied or even triggered by slow-slip events "and vice versa", she said.

“It could go either way – [the slow-slip quake] can increase stress in areas or decrease stress. It hasn’t altered our perception of just how often [big earthquakes in Wellington] will occur.”

One example of this connection was the February earthquake “swarm” off the coast of Wairoa, which was thought to trigger a slow-slip event in Hawke’s Bay.

The Kapiti area had previously experienced two slow-slip quakes, one in 2003 and another in 2008. Being five years apart, this year's event had arrived just as GeoNet anticipated.

“Based on these last two events, we think that this should go on for roughly a year. The longest one has gone on for 400 days.”

Scientists believed slow-slip events happened further down in the crust from “fast-slip”, felt earthquakes, between its solid rock and more liquid forms.

Recurring slow-slip events have also been recorded in Manawatu, Hawke’s Bay and Gisborne.


The Dominion Post