December 2010 Christchurch earthquake

A magnitude 7.1 Mw earthquake, known as the Darfield earthquake, occurred on 4 September 2010, and had, at the time, the biggest ground shaking ever to be recorded in New Zealand, at 1.26 g (1.26 times the acceleration of gravity). The Darfield quake occurred along the Greendale Fault, and had thousands of shallow aftershocks over the coming months. Most occurred along the fault's surface trace, but there was also a zone of aftershocks extending northwards from the middle of the fault trace, as well as beyond the western and eastern (towards Christchurch) sides. The Boxing Day aftershock occurred in the eastern cluster. however a few did, including a magnitude 5.0 quake on 19 October, a magnitude 4.7 quake on 14 November, the Boxing Day quake and the 22 February 2011 earthquake. The February earthquake caused 185 deaths and tens of billion dollars in damage. == Earthquake ==

The earthquake occurred at 10:30a.m. on Boxing Day, 26 December 2010, and had a moment magnitude () of 4.7 and local magnitude () of 4.9. The hypocentre was located under the city, with an epicentre near Barbadoes Street, or northwest of Christ Church Cathedral. and the 17th biggest since the sequence began in September. The maximum peak ground acceleration measured 0.4g, at Christchurch Botanic Gardens. By contrast, the Darfield earthquake had peak ground accelerations in the central city ranging up to 0.3 g. The Boxing Day earthquake was followed by an aftershock sequence in the same area, with 'two dozen' occurring in the first 36 hours, and more than 30 occurring within three-to-four weeks. They mostly occurred within a area, at depths of , along a steeply dipping strike-slip fault striking east–northeast. Activity on that fault was spread over a distance of about . Five aftershocks had magnitudes of at least , and 20 measured or greater. Because the earthquake did not occur on the Greendale Fault that ruptured in the Darfield earthquake, the Boxing Day earthquake does not fit GNS Science's definition of an aftershock, which should occur on the same fault. As it is likely that the Boxing Day earthquake resulted from the stress changes following the Darfield earthquake, it can be 'loosely' considered an aftershock. == Damage and effects ==

The Boxing Day earthquake caused "significant" damage to Christchurch, Of the 3,000 buildings inspected within a day of the earthquake (out of 5,000) in Four Avenues, 115 needed repairs. A few walls collapsed including the Southern Encounter Aquarium building in Cathedral Square. Several buildings had a few cracks form and bricks loosened. Some sprinkler pipes broke There was no damage to the water, wastewater or stormwater networks, and there were no reports of injuries. By 6 January, the Earthquake Commission had received 3,500 damage compensation claims, the 19 October earthquake had 2,139 claims on 6 January and the 14 November aftershock had 1,986. This was also more than the 6,200 claims received after the 2007 Gisborne earthquake. An expert panel report commissioned by the Department of Building and Housing concluded that the Boxing Day and Darfield quakes "did not significantly reduce the earthquake resistance" of four major buildings that experienced building failure in the February 2011 earthquake: the CTV Building, the PGC Building, the Hotel Grand Chancellor building and the Forsyth Barr Building. == Response ==

Shortly after the earthquake, hundreds of shoppers were evacuated from the Westfield Riccarton shopping mall. In the late afternoon, these restricted zones were slowly scaled back, Police made three arrests relating to the cordons. To recoup for these losses, Boxing Day sales were re-run on 12 February 2011. It was launched by Mayor Bob Parker and Earthquake Recovery Minister Gerry Brownlee at City Mall, and received funding from the government, the city council and earthquake trusts. Despite claims that New Year's Eve celebrations at Cathedral Square had to be relocated due to the damage, it did not happen. After structural assessments determined that there was no public danger, the council decided that the celebrations would continue and expected 15,000 attendees. == See also==