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.
The earthquake occurred during lunch time, when many people were on the city streets. More than 110 fatalities were from the collapse of two multi-storey office buildings – the Canterbury Television and Pyne Gould Corporation buildings. Falling bricks and masonry on Manchester Street and Cashel Mall killed 11 people, and six died in two city buses crushed by crumbling walls. Rock cliffs behind houses collapsed in the Sumner and Redcliffs area, and boulders tumbled from the Port Hills summits, with five people killed by falling rocks.
Although not as powerful as the magnitude 7.1 earthquake on 4 September 2010, this earthquake occurred on a faultline 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 the ground motion produced by the September 2010 earthquake.
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 was Christchurch’s tallest building, the Hotel Grand Chancellor. Nearly a third of the buildings in the central business district are expected to be demolished.
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 will have to be demolished, and some sections of suburbs will probably never be re-occupied.
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 a month after the earthquake. Electricity was restored to 75% of the city within three days, but water supplies and sewerage systems took a number of weeks to restore in areas affected by liquefaction.
* The official toll was initially given as 181 but four further victims were confirmed by the coroner in February 2012
Text adapted from Te Ara with acknowledgements to GeoNet and GNS Science