Three-month quake without the shake

SLOW-SLIP EVENT OVER: GNS Science geophysicist Dr Laura Wallace says many small to moderate earthquakes in this area appeared to track a slow-slip movement, also known as a silent earthquake, which lasted three months.
File picture

A silent earthquake off the East Coast has ended after three months, scientists say.

Monitoring equipment first started recording a slow-slip event (also known as a silent earthquake) during the last week of March.

GNS Science geophysicist Laura Wallace said the event ended about three weeks ago in mid-June.

“During the slow-slip event we recorded many small to moderate earthquakes in the area, including a magnitude 5.1 on May 14.

“While these quakes have also tapered off, a model showing the evolution of the event indicates that many of the earthquakes appear to track the slow-slip movement.

“Our scientists have over two dozen instruments beneath Poverty Bay and Hawke’s Bay that are recording seafloor movement and earthquakes during slow-slip events.

“In November, these instruments will be collected and the data they provide will help give us a better picture of what happened during this event.”

Dr Wallace said total movement along the Hikurangi Subduction Zone during the event was estimated to be about 20 to 30 centimetres, which was equivalent to roughly four to five years of plate motion there.

“To look at it another way, if this had ruptured in a single, instantaneous fault rupture (or what we consider a typical earthquake), it would likely have been similar to a magnitude 7.0 earthquake.

“Our scientists had been anticipating this slow-slip event.

“That’s why we have instruments on the seafloor right now recording movement.

“Our slow-slip record has shown regular events every one-to-two years, with much larger events every four-to-six years.

“This most recent slow-slip event appears to be the largest event we’ve seen offshore of the East Coast and is slightly larger than the 2010 Gisborne slow-slip event — previously the largest we have observed in that area.

“Slow-slip events are quite common in this part of New Zealand due to the subducting Pacific Plate moving westward under the Australian Plate.

“We started detecting slow-slip events in 2002 after installing a GPS (Global Positioning System) network around New Zealand to monitor land movement.

“Slow-slip events are undetectable by both humans and our seismograph network because they move faults over weeks to months instead of within seconds like the earthquakes that you typically think of.”

A silent earthquake off the East Coast has ended after three months, scientists say.

Monitoring equipment first started recording a slow-slip event (also known as a silent earthquake) during the last week of March.

GNS Science geophysicist Laura Wallace said the event ended about three weeks ago in mid-June.

“During the slow-slip event we recorded many small to moderate earthquakes in the area, including a magnitude 5.1 on May 14.

“While these quakes have also tapered off, a model showing the evolution of the event indicates that many of the earthquakes appear to track the slow-slip movement.

“Our scientists have over two dozen instruments beneath Poverty Bay and Hawke’s Bay that are recording seafloor movement and earthquakes during slow-slip events.

“In November, these instruments will be collected and the data they provide will help give us a better picture of what happened during this event.”

Dr Wallace said total movement along the Hikurangi Subduction Zone during the event was estimated to be about 20 to 30 centimetres, which was equivalent to roughly four to five years of plate motion there.

“To look at it another way, if this had ruptured in a single, instantaneous fault rupture (or what we consider a typical earthquake), it would likely have been similar to a magnitude 7.0 earthquake.

“Our scientists had been anticipating this slow-slip event.

“That’s why we have instruments on the seafloor right now recording movement.

“Our slow-slip record has shown regular events every one-to-two years, with much larger events every four-to-six years.

“This most recent slow-slip event appears to be the largest event we’ve seen offshore of the East Coast and is slightly larger than the 2010 Gisborne slow-slip event — previously the largest we have observed in that area.

“Slow-slip events are quite common in this part of New Zealand due to the subducting Pacific Plate moving westward under the Australian Plate.

“We started detecting slow-slip events in 2002 after installing a GPS (Global Positioning System) network around New Zealand to monitor land movement.

“Slow-slip events are undetectable by both humans and our seismograph network because they move faults over weeks to months instead of within seconds like the earthquakes that you typically think of.”

Your email address will not be published. Comments will display after being approved by a staff member. Comments may be edited for clarity.

Poll

  • Voting please wait...
    Your vote has been cast. Reloading page...
    Do you support the new identity and wellbeing focus of Trust Tairawhiti (formerly Eastland Community Trust)?