On Tuesday 22 February 2011 at 12.51 p.m. Christchurch was badly damaged by a magnitude 6.3 earthquake, which killed 185 people and injured several thousand. The earthquake epicentre was near Lyttelton, just 10 kilometres south-east of Christchurch’s central business district. The earthquake occurred more than five months after the 4 September 2010 earthquake, but is considered to be an aftershock of the earlier quake.
Casualties and damage
One hundred and eighty five people died as a result of the 22 February earthquake. It was lunchtime and many people were on the city streets. One hundred and fifteen died in the CTV building, 18 in the PGC building, 36 in the central city (including eight on buses), and 12 in the suburbs (including from falling rocks in the Redcliffs, Sumner and Port Hills). The Chief Coroner determined that another four deaths were directly associated with the earthquake. (A complete list of the deceased can be found on the New Zealand Police website.)
The earthquake brought down many buildings previously damaged in the September 2010 earthquake, especially older brick and mortar buildings. Many heritage buildings were heavily damaged, including the Provincial Council Chambers, Lyttelton’s Timeball Station, and both the Anglican Christchurch Cathedral and the Catholic Cathedral of the Blessed Sacrament. Among the modern buildings damaged, and eventually demolished, was Christchurch’s tallest building, the Hotel Grand Chancellor. Over a quarter of the buildings in the central business district were demolished.
A violent earthquake
Although not as powerful as the magnitude 7.1 earthquake on 4 September 2010, this earthquake occurred on a fault line that was shallow and close to the city, so the shaking was particularly destructive. In the February 2011 quake, the fault movement and structure of the bedrock produced exceptionally strong ground motion – up to 1.8 times the acceleration due to gravity in the eastern suburbs. In the city centre ground accelerations were three to four times greater than those produced by the September 2010 earthquake.
Liquefaction was much more extensive than in the September 2010 earthquake. Eastern sections of the city were built on a former swamp. Shaking turned water-saturated layers of sand and silt beneath the surface into sludge that squirted upwards through cracks. Properties and streets were buried in thick layers of silt, and water and sewage from broken pipes flooded streets. House foundations cracked and buckled, wrecking many homes. Despite the damage to homes, there were few serious injuries in residential houses in liquefaction areas. However, several thousand homes had to be demolished, and a large area of eastern Christchurch will probably never be reoccupied.
Aftermath and exodus
The government immediately activated its National Crisis Management Centre, and declared a national state of emergency the day after the quake. Christchurch’s central business district remained cordoned off for more than two years after the earthquake. Electricity was restored to 75% of the city within three days, but water supplies and sewerage systems took several years to restore in some areas affected by liquefaction.
In the weeks following the earthquake about 70,000 people were believed to have left the city due to uninhabitable homes, lack of basic services and continuing aftershocks. Timaru’s population swelled by 20% and thousands of pupils registered at schools in other cities and towns. Many returned to Christchurch as conditions improved.
Fault beneath the Port Hills
The earthquake was caused by the rupture of a 15-kilometre-long fault along the southern edge of the city, from Cashmere to the Avon–Heathcote estuary. The fault slopes southward beneath the Port Hills and did not break the surface – scientists used instrument measurements to determine its location and movement.