A major earthquake occurred in Christchurch on Tuesday 22 February 2011 at 12:51 p.m. local time (23:51 UTC, 21 February). The M_w6.2 (M_L6.3) earthquake struck the Canterbury Region in the South Island, centred 6.7 kilometres (4.2 mi) south-east of the central business district. It caused widespread damage across Christchurch, killing 185 people in New Zealand's fifth-deadliest disaster. Scientists classified it as an intraplate earthquake and a potential aftershock of the September 2010 Canterbury earthquake.

Christchurch's central city and eastern suburbs were badly affected, with damage to buildings and infrastructure already weakened by the 2010 Canterbury earthquake and its aftershocks. Significant liquefaction affected the eastern suburbs, producing around 400,000 tonnes of silt. The earthquake was felt across the South Island and parts of the lower and central North Island. While the initial quake only lasted for approximately 10 seconds, the damage was severe because of the location and shallowness of the earthquake's focus in relation to Christchurch as well as previous quake damage. Subsequent population loss saw the Christchurch main urban area fall behind the Wellington equivalent, to decrease from second- to third-most populous area in New Zealand. Adjusted for inflation, the 2010–2011 Canterbury earthquakes caused over $52.2 billion in damage, making it New Zealand's costliest natural disaster and one of the most expensive disasters in history.

The 2011 Christchurch Earthquake was a 6.3-magnitude intraplate earthquake. It may have been an aftershock of the 7.1-magnitude 4 September 2010 Canterbury earthquake. New Zealand's GNS Science has stated that the earthquake was part of the aftershock sequence that has been occurring since the September magnitude-7.1 quake, however a seismologist from Geoscience Australia considers it a separate event given its location on a separate fault system.

Although smaller in magnitude than the 2010 earthquake, the February earthquake was more damaging and deadly for a number of reasons. The epicentre was closer to Christchurch, and shallower at 5 kilometres (3 mi) underground, whereas the September quake was measured at 10 kilometres (6 mi) deep. The February earthquake occurred during lunchtime on a weekday when the CBD was busy, and many buildings were already weakened from the previous quakes. The peak ground acceleration (PGA) was extremely high, and simultaneous vertical and horizontal ground movement was "almost impossible" for buildings to survive intact. Liquefaction was significantly greater than that of the 2010 quake, causing the upwelling of more than 200,000 tonnes of silt which needed to be cleared. The increased liquefaction caused significant ground movement, undermining many foundations and destroying infrastructure, damage which "may be the greatest ever recorded anywhere in a modern city". 80% of the water and sewerage system was severely damaged. The earthquake also caused an increased spring activity in the Avon and Heathcote Rivers.

GNS Science stated that the earthquake arose from the rupture of an 8 km x 8 km fault running east-northeast at a depth of 1–2 km beneath the southern edge of the Avon-Heathcote Estuary and dipping southwards at an angle of about 65 degrees from the horizontal beneath the Port Hills."

While both the 2010 and 2011 earthquakes occurred on "blind" or unknown faults, New Zealand's Earthquake Commission had, in a 1991 report, predicted moderate earthquakes in Canterbury with the likelihood of associated liquefaction.

Initial measurement of peak ground acceleration (PGA) in central Christchurch exceeded 1.8 g (i.e. 1.8 times the acceleration of gravity), with the highest recording 2.2 g, at Heathcote Valley Primary School, a shaking intensity equivalent to MMI X+. Subsequent analysis revised the Heathcote Valley Primary School acceleration down to 1.37 g, with the 1.89 g reading at Pages Road Pumping Station in Christchurch revised down to 1.51 g. Nevertheless, these were the highest PGAs ever recorded in New Zealand; the highest reading during the September 2010 event was 1.26 g, recorded near Darfield. The PGA is also one of the greatest-ever ground accelerations recorded in the world, and was unusually high for a 6.2 quake, and the highest in a vertical direction. The central business district (CBD) experienced PGAs in the range of 0.574 and 0.802 g. As a comparison, the 7.0 M_w 2010 Haiti earthquake had an estimated PGA of 0.5 g. The acceleration occurred mainly in a vertical direction, with eyewitness accounts of people being tossed into the air.

The maximum Modified Mercalli intensity was assigned XI (Extreme).