Recent Chch quakes within 'expected aftershock sequence'

Photo: File image
Photo: File image
Christchurch is still experiencing a higher rate of earthquakes than it was before 2010, but they are within the expected behaviour of the 2010 aftershock sequence, Geonet says.

Over the past week, GeoNet recorded 10 earthquakes south-west of Christchurch, between magnitude 1.2 and 3.5.

The largest event occurred at 5.45pm on Saturday, June 15, for which it received more than 4000 felt reports.

"The M3.5 event was shallow at 4km deep, which explains why it was felt by many in the area surrounding the earthquake epicentre," a spokesperson said.

"Seismicity in the Canterbury region is still at higher levels than before 2010, this includes the earthquakes GeoNet is recording around Christchurch. 

"However, this is within the expected behaviour for the 2010 Canterbury aftershock sequence, even after more than a decade since the 2010-2011 earthquakes."

Image showing about 90 earthquakes recorded in the last year between M1.2 and M3.5, 13 of them...
Image showing about 90 earthquakes recorded in the last year between M1.2 and M3.5, 13 of them were above M3. The largest is the M3.5 of the evening of 15 June. Image: Geonet
GNS scientists continue to closely monitor and produce earthquake forecasts for the Canterbury region generated by computer models.

"Aftershock sequences typically quieten down over time – but it can take years, decades or even centuries for seismicity in a region to return to a pre-influenced - before the mainshock - state.

"It is difficult to attribute small magnitude earthquakes to a specific fault, but the events we have recorded in the past week fall within the region that ruptured during the M6.2 February 2011 Christchurch earthquake and the area where we have recorded aftershock events over the past 13 years.

"We understand that some people might find these earthquakes unsettling. The All Right? website has great resources where you can read and talk about any concerns that you have.

"Even though the events of the past week are consistent with what we observed for the Canterbury region in the past few years, every earthquake is a good reminder to be prepared. And to remember that drop, cover, hold is the right action to take during an earthquake."