Earthquake in Christchuurch

A 6.3 earthquake occurred in Christchurch on 22 February 2011 at 12:51 p.m. local time. The earthquake struck the Canterbury Region in New Zealand's South Island and was centred 2 kilometres west of the port town of Lyttelton, and 10 kilometres south-east of the centre of Christchurch, at the time New Zealand's second-most populous city.The earthquake occurred more than five months after the 4 September 2010 earthquake, but is considered to be an aftershock of the earlier quake.

What caused the earthquake?

In New Zealand, the Australian and Pacific Plates push against each other along a curving boundary. At the southern end of the South Island, the Australian Plate dives down (subducts) below the Pacific Plate whilst in the North Island the opposite situation occurs with the Pacific Plate being pushed under by the Australian Plate. In between, through most of the South Island, the two plates grind past each other along the Alpine Fault. The earthquake occurred on a conservative plate margin where the Pacific Plate slid past the Australian Plate in the opposite direction. It was technically an aftershock from a larger earthquake in 2010 but the impacts were more severe.

Primary

• Ground shaking: The ground was violently shaken and caused it to rise by up to 1 metre in places.

• Liquefaction: When the ground was shaken, the water was brought to the surface and this made the ground very soft and everything from buildings to roads to cars and trees sunk into the ground. Sand boils were the most common type of liquefaction in this earthquake.

• Slope failure: Part of the country’s longest glacier was broken off creating a large iceberg (size of 20 football fields). Significant landslides and rock falls in the Port Hills in the southern part of Christchurch were reported.

• Tsunami: 3.5m (11ft) tsunami waves in Tasman Lake, following quake-triggered glacier calving from Tasman Glacier.

Secondary

• Building/infrastructure failure: Many had been weakened by the 2010 earthquake and although many survived that earthquake, they were destroyed by the 2011 earthquake. All types of buildings were affected and even some modern earthquake-proof buildings succumbed to the quake.

• Fire: A collapsed building at King’s education in Christchurch had to be extinguished in order to recue people trapped inside.

• Water shortage/contamination: Water & sewage pipes were ruptured during the quake and this allowed them to mix and contaminate the water. As a result, lots of bottled water had to be supplied to people with no access to clean water.

• Exposure/housing: Thousands of people had to move out of their homes as it was unsafe for them to stay as their homes may have been weakened by the quake and could collapse in an aftershock. There were no reports of famine or disease.

• Hazard-resistant design (hint: consider existing and future buildings): Damaged buildings had different coloured cards placed on them to indicate how damaged they were (Green: Safe, through to Red: Unsafe, must be demolished). Earthquake commission funds Geonet it also funds programs for people Quakesafe their homes. The AMI stadium has been reinforced by 10m stone columns which can stop liquefaction.

• Community education and preparedness: In New Zealand regular earthquake drills are carried out to ensure people know what to do. Plus all buildings are made life safe ensure that they will not collapse in case of an earthquake. Any old buildings have been retrofitted to withstand future earthquakes.

• Land-use planning: Homes are no longer being rebuilt in seismically dangerous zones. The government has instigated purchases of both land and houses in high risk zones and works with insurance companies to accelerate safe recovery (Canterbury Earthquake Recovery Authority, 2012).

• Insurance: $898 million has been paid in building claims.

• Aid: St John’s ambulance had 16 ambulances operational within half an hour of the quake. International aid was provided in the form of money (around $6-7 million) and aid workers.

• Development of the earthquake prediction systems: Geonet detects and monitors earthquakes can provide emergency services with info within a few minutes of an earthquake.