GeoNet takes a look back at the big movers and shakers of 2010.
On Saturday, September 4 at 4:35 am the most damaging earthquake in New Zealand since the 1931 Hawke’s Bay earthquake
occurred near Darfield, 40 km west of Christchurch, causing significant damage in the Canterbury region.
The magnitude 7.1 earthquake
had a depth of 10 km, and was reported felt across New Zealand from Northland to Stewart Island. In mid-Canterbury damage was severe, with many buildings destroyed or damaged beyond repair and services disrupted. A fault trace of length about 25 km running roughly from west to east appeared, and widespread liquefaction and some landslides and slips resulted. That there was no loss of life was remarkable, and due mainly to the fact that the earthquake occurred at a time when human activity was minimal.
Aftershocks have occurred at distances of over 40 km from the mainshock, and many of these also caused severe damage, often to buildings weakened by earlier earthquakes.
There have been 11 aftershocks of magnitude 5.0 or greater, the largest a 5.6 that occurred 20 minutes after the mainshock.
The most damaging have all been located within 10 km of Christchurch city and at shallow depths of about 5 km. These include a magnitude 5.0 on September 8 at 7:49 am, a 5.1 on October 19 at 11:32 am and a 4.9 on Boxing Day at 10:30 am, all of which caused serious damage and disruption.
Earthquakes other than those in the Canterbury region that caused minor damage and were of magnitude 5.0 and greater were:
- July 12, a magnitude 5.3 earthquake centred 10 km north-west of Wairoa at a depth of 40 km was felt from Whakatane to Hastings and caused goods to fall from shelves in Gisborne, Tuai and Wairoa.
- August 25, a magnitude 5.1 centred 30 km south-west of Whanganui at a depth of 30 km was felt mainly throughout the lower North Island, with goods falling from shelves in Whanganui.
- September 7, a shallow magnitude 5.2 earthquake centred 10 km south-east of Porangahau was felt from Hastings to Wellington and caused minor damage in Porangahau. A similarly located event of magnitude 5.3 on September 9 had a similar felt pattern, although no damage was reported.
- November 28, a magnitude 5.4 earthquake centred 10 km north-west of Masterton and at a depth of 30 km was felt throughout the lower North Island, with minor contents damage reported in Masterton, Carterton and Otaki. Three aftershocks were also reported felt.
The largest deep earthquake was a magnitude 6.5 event on September 29. This was centred 80 km north of White Island at a depth of 290 km and was felt from Northland to Christchurch, most strongly along the eastern side of the North Island, which is characteristic of deep North Island earthquakes.
There were four earthquakes outside the New Zealand region that were reported felt.
The most significant, on June 18, was a magnitude 5.9 event centred 500 km north-east of East Cape at a depth of 200 km. It was felt at scattered locations throughout the North Island.
In 2010, a total of 39 earthquakes of magnitude 5.0 or greater occurred in New Zealand, of which 11 were at depths of greater than 100 km. About 1,600 earthquakes have been reported felt, and all significant damage was caused by the Darfield earthquake and its aftershocks. The Earthquake Commission has so far received 163,000 claims, and the latest estimate of the cost of damage is around NZ$4 billion.