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’s epicentre was near Lyttelton, just 10 km south-east of Christchurch’s central business district. The earthquake occurred nearly six months after the 4 September 2010 earthquake, but is considered to be an aftershock of the earlier quake.
The earthquake occurred at lunchtime, when many people were on the city streets. More than 110 fatalities were caused by the collapse of two multi-storey office buildings – the Canterbury Television and Pyne Gould Corporation buildings. Falling bricks and masonry on Manchester St and in 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 down the Port Hills, 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 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.
The earthquake brought down many buildings that had been damaged in September 2010, 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 irrevocably damaged was Christchurch’s tallest building, the Hotel Grand Chancellor. More than half of the buildings in the central business district have had 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, 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 reoccupied.
The government immediately activated its National Crisis Management Centre, and a national state of emergency was declared the day after the quake. Christchurch’s central business district was quickly cordoned off. Electricity was restored to 75% of the city within three days, but re-establishing water supplies and sewerage systems took much longer.
The cordon around the central business district was progressively reduced over the next two years but not completely removed until June 2013. It is expected to take several years to completely restore the city’s electricity and water networks to pre-earthquake standards. Many areas in the condemned ‘Red Zone’ will not have services restored to this standard, but temporary repairs have been made while residents remain.
* The official toll was initially 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