Christchurch earthquakes

A major earthquake occurred in Christchurch on Tuesday 22 February 2011 at 12:51 p.m. local time (23:51 UTC, 21 February). The () earthquake struck the entire of the Canterbury region in the South Island, centred south-east of the central business district. It caused widespread damage across Christchurch, killing 185 people, in New Zealand's fifth-deadliest disaster.

Christchurch's central city and eastern suburbs were badly affected, with damage to buildings and infrastructure already weakened by the magnitude 7.1 Canterbury earthquake of 4 September 2010 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.

Geology

The 6.3-magnitude earthquake 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. According to GNS Science seismologists, the energy released in Christchurch was equivalent to a magnitude 6.7 earthquake.

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 underground, whereas the September quake was measured at 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.

Fault

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.

Intensity

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 upwards (positive acceleration) was greater than the downwards, which had a maximum recording of 0.9 ''g''; the maximum recorded horizontal acceleration was 1.7 ''g'' The force of the earthquake was "statistically unlikely" to occur more than once in 1000 years, according to one seismic engineer, with a PGA greater than many modern buildings were designed to withstand. Although the rupture was subsurface, satellite images indicated that the net displacement of the land south of the fault was 50 cm westwards and upwards; the land movement would have been greater during the earthquake. Land movement was varied around the area horizontally—in both east and west directions—and vertically; the Port Hills were raised by 40 cm.

The earthquake was a "strike-slip event with oblique motion" which caused mostly horizontal movement with some vertical movement, with reverse thrust causing upwards vertical movement. The vertical acceleration was far greater than the horizontal acceleration.

The current New Zealand building code requires a building with a 50-year design life to withstand predicted loads of a 500-year event. Initial reports by GNS Science suggested that ground motion "considerably exceeded even 2500-year design motions", beyond maximum considered events (MCE). By comparison, the 2010 quake—in which damage was predominantly to pre-1970s buildings—exerted 65% of the design loading on buildings. The acceleration experienced in February 2011 would "totally flatten" most world cities, causing massive loss of life; in Christchurch, New Zealand's stringent building codes limited the disaster. It is also possible that "seismic lensing" contributed to the ground effect, with the seismic waves rebounding off the hard basalt of the Port Hills back into the city. Geologists reported liquefaction was worse than the 2010 earthquake.

Aftershocks

The earthquake generated a significant series of its own aftershocks. More than 361 aftershocks occurred in the first week following the magnitude 6.3 earthquake.

* The largest was a magnitude 5.9 tremor which occurred just under two hours after the main earthquake.
* A 5.3-magnitude aftershock on 16 April, the largest for several weeks, caused further damage, including power cuts and several large rock falls.
* An aftershock from the Greendale Fault measuring 5.3 on the Richter scale hit the region on 10 May 2011. It cut power to homes and businesses for several minutes and caused further damage to buildings in the city centre. No deaths or injuries were reported. It was felt as far away as Dunedin and Greymouth.
* On 6 June, a large aftershock measuring 5.5 on the Richter scale occurred and was felt as far away as Kaikoura and Oamaru.
* A series of aftershocks occurred on 13 June. A tremor of 5.7 on the Richter scale was felt at 1 pm NZT, with a depth of 9 km, its epicentre at Taylors Mistake. A 6.0 tremor occurred just over an hour later, with a depth of 7 km, located 5 km south-east of the city. Power was cut to around 54,000 homes, with further damage and liquefaction in already weakened areas. The Lyttelton Timeball Station collapsed and Christchurch Cathedral sustained more damage. At least 46 people were reported injured. These were followed by a magnitude 5.4 quake at a depth of 8 km and centred 10 km south-west of Christchurch at 10:34 pm on 21 June 2011.
* 23 December 2011 featured another series of strong shocks, including a 5.8 at 1:58pm and a 6.0 at 3:18pm. The earthquakes interrupted power and water supplies, three unoccupied buildings collapsed and there was again liquefaction in eastern suburbs and rockfalls in hill areas. One person died after tripping on uneven ground caused by the earthquake.

Below is a list of all aftershocks of Richter, moment, and body-wave magnitudes 5.0 and above that occurred in the region between 22 February 2011 and 15 January 2012.

Damage and effects

Road and bridge damage occurred and hampered rescue efforts. Soil liquefaction and surface flooding also occurred. Road surfaces were forced up by liquefaction, and water and sand were spewing out of cracks. A number of cars were crushed by falling debris. In the central city, two buses were crushed by falling buildings. Because the earthquake hit during the lunch hour, some people on the footpaths were buried by collapsed buildings.

Central city

Damage occurred to many older buildings, particularly those with unreinforced masonry and those built before stringent earthquakes codes were introduced. On 28 February 2011, the Prime Minister announced that there would be an inquiry into the collapse of buildings that had been signed off as safe after the previous earthquake on 4 September 2010, "to provide answers to people about why so many people lost their lives."

Of the 3,000 buildings inspected within the four avenues which bound the central business district by 3 March 2011, 45% had been given red or yellow stickers to restrict access because of the safety problems. Many heritage buildings were given red stickers after inspections. As of February 2015, there had been 1240 demolitions within the bounds of the four avenues since the September 2010 earthquakes.

The six-storey Canterbury Television (CTV) building collapsed in the earthquake, leaving only its lift shaft standing, which caught fire. 115 people died in the building, which housed a TV station, a medical clinic and an English language school. On 23 February police decided that the damage was not survivable, and rescue efforts at the building were suspended. Fire-fighting and recovery operations resumed that night, later joined by a Japanese search and rescue squad. Twelve Japanese students from the Toyama College of Foreign Languages died in the building collapse. A government report later found that the building's construction was faulty and should not have been approved.

The four-storey Pyne Gould Guinness (PGC) House on Cambridge Terrace, headquarters of Pyne Gould Corporation, collapsed, with 18 casualties. On Wednesday morning, 22 hours after the quake, a survivor was pulled from the rubble. The reinforced concrete building had been constructed in 1963–1964.

The Forsyth Barr Building survived the earthquake but many occupants were trapped after the collapse of the stairwells, forcing some to abseil out after the quake. Search of the building was technically difficult for USAR teams, requiring the deconstruction of 4-tonne stair sets, but the building was cleared with no victims discovered.

The earthquake destroyed the ChristChurch Cathedral's spire and part of its tower, and severely damaged the structure of the remaining building. The remainder of the tower was demolished in March 2012. The west wall suffered collapses in the June 2011 earthquake and the December 2011 quake due to a steel structure – intended to stabilise the rose window – pushing it in. The Anglican Church decided to demolish the building and replace it with a new structure, but various groups opposed the church's intentions, with actions including taking a case to court. While the judgements were mostly in favour of the church, no further demolition occurred after the removal of the tower in early 2012. Government expressed its concern over the stalemate and appointed an independent negotiator and in September 2017, the Christchurch Diocesan Synod announced that ChristChurch Cathedral will be reinstated after promises of extra grants and loans from local and central government. By mid-2019 early design and stabilisation work had begun. Since 15 August 2013 the cathedral congregation has worshipped at the Cardboard Cathedral.

Christchurch Hospital was partly evacuated due to damage in some areas, but remained open throughout to treat the injured.

On 23 February, Hotel Grand Chancellor, Christchurch's tallest hotel, was reported to be on the verge of collapse. The 26-storey building was displaced by half a metre in the quake and had dropped by 1 metre on one side; parts of the emergency stairwells collapsed. The building was thought to be irreparably damaged and have the potential to bring down other buildings if it fell; an area of a two-block radius around the hotel was thus evacuated. The building was eventually stabilised and, on 4 March it was decided the building would be demolished over the following six months, so that further work could be done with the buildings nearby. Demolition was completed in May 2012. The 21-storey PricewaterhouseCoopers building, the city's tallest office tower, was among the office buildings to be later demolished.

The Carlton Hotel, a listed heritage building, was undergoing repairs after the September 2010 earthquake damage when the February 2011 earthquake damaged the building further. It was deemed unstable and demolished in April 2011. St Elmo Courts had been damaged in the September 2010 earthquake and the owner intended to repair the building, but further damage caused by the February 2011 event resulted in a decision to demolish, which was done the following month.

The historic Canterbury Provincial Council Buildings were severely damaged, with the Stone Chamber completely collapsing.

The second civic office building of Christchurch City Council, Our City, had already been damaged in the September earthquake and was heavily braced following the February event.

The Civic, the council's third home, was heavily damaged in February and was demolished. Both Our City and the Civic are on the register of Heritage New Zealand.

The Catholic Cathedral of the Blessed Sacrament was also severely damaged, with the towers falling. A decision was made to remove the dome because the supporting structure was weakened.

Several other churches were seriously damaged, including: Knox Presbyterian Church, St Luke's Anglican Church, Durham Street Methodist Church, St Paul's-Trinity-Pacific Presbyterian Church, Oxford Terrace Baptist Church, Holy Trinity Avonside and Holy Trinity, Lyttelton. Sydenham Heritage Church and the Beckenham Baptist Church were heavily damaged, and then demolished days after the earthquake. Concrete block construction fared badly, leaving many modern iconic buildings damaged.

Suburbs

On 7 March, Prime Minister John Key said that around 10,000 houses would need to be demolished, and liquefaction damage meant that some parts of Christchurch could not be rebuilt on.

;Residential red zone
Several areas in and around Christchurch were deemed infeasible to rebuild due to earthquake damage resulting from soil liquefaction and rockslides. These areas were placed into a residential red zone.

;Lyttelton
Buildings in Lyttelton sustained widespread damage, with a fire officer reporting that 60% of the buildings in the main street had been severely damaged. Two people died on local walking tracks after being hit by rockfalls. The town's historic Timeball Station was extensively damaged, adding to damage from the preceding earthquake in September 2010. The station collapsed on 13 June 2011 after a magnitude 6.0 aftershock. In 2013, it was announced that the tower and ball would be restored, and that funds were to be sought from the community to rebuild the rest of the station. The restoration was completed in 2018 with the site being reopened in November.

;Sumner
Landslides occurred in Sumner, crushing buildings. Parts of Sumner were evacuated during the night of 22 February after cracks were noticed on a nearby hillside. Three deaths were reported in the Sumner area, according to the Sumner Chief Fire Officer. The Shag Rock, a notable landmark, was reduced to half of its former height.

;Redcliffs
In contrast to the September 2010 earthquake, Redcliffs and the surrounding hills suffered severe damage. The cliff behind Redcliffs School collapsed onto the houses below. Large boulders were found on the lawns of damaged houses.

Twelve streets in Redcliffs were evacuated on the night of 24 February 2015 after some cliffs and hills surrounding Redcliffs were deemed unstable.

Redcliffs Primary School, then located at 140 Main Road, right under the cliffs, was moved to Van Asch Deaf Education Centre, 4.5 km from the main site soon afterwards. After 9 years, the school was moved to Redcliffs Park, reopening in July 2020. The cost of the rebuild was $16 million.

Beyond Christchurch

The quake was felt as far north as Tauranga and as far south as Invercargill, where the 111 emergency network was rendered out of service.

At the Tasman Glacier some from the epicentre, around 30 million tonnes (33 million ST) of ice tumbled off the glacier into Tasman Lake, hitting tour boats with tsunami waves high.

KiwiRail reported that the TranzAlpine service was terminating at Greymouth and the TranzCoastal terminating at Picton. The TranzAlpine was cancelled until 4 March, to allow for personnel resources to be transferred to repairing track and related infrastructure, and moving essential freight into Christchurch, while the TranzCoastal was cancelled until mid-August. KiwiRail also delayed 14 March departure of its Interislander ferry to Singapore for a extension and refit prior to the 2011 Rugby World Cup. With extra passenger and freight movements over Cook Strait following the earthquake, the company would have been unable to cope with just two ships operating on a reduced schedule so soon after the earthquake, so pushed back the departure to the end of April.

The earthquake combined with the urgency created by the unseasonably early break-up of sea ice on the Ross Ice Shelf caused logistical problems with the return of Antarctic summer season research operations from Scott Base and McMurdo Station in Antarctica to Christchurch.

Casualties

185 people from more than 20 countries died in the earthquake. Over half of the deaths occurred in the six-storey Canterbury Television (CTV) Building, which collapsed and caught fire in the earthquake. A state of local emergency was initially declared by the Mayor of Christchurch, which was superseded when the government declared a state of national emergency, which stayed in force until 30 April 2011.

Of the 185 victims, 115 people died in the CTV Building alone, while another 18 died in the collapse of PGC House, and eight were killed when masonry fell on Red Bus number 702 in Colombo Street. In each of these cases the buildings that collapsed were known to have been appreciably damaged in the September 2010 earthquake but the local authority had permitted the building to be re-occupied (CTV and PGC buildings) or protective barriers adjacent to them moved closer to areas at risk of falling debris (Colombo Street). An additional 28 people were killed in various places across the city centre, and twelve were killed in suburban Christchurch. Due to the injuries sustained some bodies remained unidentified. Between 6,600 and 6,800 people were treated for minor injuries, and Christchurch Hospital alone treated 220 major trauma cases connected to the quake.
Rescue efforts continued for over a week, then shifted into recovery mode. The last survivor was pulled from the rubble the day after the quake.

The nationalities of the deceased are as follows.

Emergency management

Immediately following the earthquake, 80% of Christchurch was without power. Water and wastewater services were disrupted throughout the city, with authorities urging residents to conserve water and collect rainwater. Prime Minister John Key confirmed that, "All Civil Defence procedures have now been activated; the Civil Defence bunker at parliament is in operation here in Wellington." It was only the second time that New Zealand had declared a national civil defence emergency; the first occasion was the 1951 waterfront dispute. The New Zealand Red Cross launched an appeal to raise funds to help victims. A full response management structure was put in place within minutes of the quake, with the Christchurch City Council's alternate Emergency Operations Centre re-established in the City Art Gallery and the regional Canterbury CDEM Group Emergency Coordination Centre (ECC) activated in its post-earthquake operational facility adjacent to the Canterbury Regional Council offices. Within two hours of the quake national co-ordination was operating from the National Crisis Management Centre located in the basement of the Beehive in Wellington.

A composite "Christchurch Response Centre" was established in the Christchurch Art Gallery, a modern earthquake-resilient building in the centre of the city which had sustained only minor damage. On 23 February the Minister of Civil Defence, John Carter declared the situation a state of national emergency, the country's first for a civil defence emergency (the only other one was for the 1951 waterfront dispute). Meanwhile, the Canterbury CDEM Group ECC had relocated to the fully operational University of Canterbury Innovation (UCi3) building to the West of the city, when the Copthorne Hotel adjacent to the Regional Council offices threatened to fall onto the offices and ECC. Once the composite Christchurch Coordination Centre was established on 23 February the CDEM Group Controllers and ECC personnel relocated to the City Art Gallery to supplement the management personnel available to the National Controller.

As per the protocols of New Zealand's Coordinated Incident Management System, the Civil Defence Emergency Management Act, and the National Civil Defence Emergency Management Plan and Guide, Civil Defence Emergency Management became lead agency—with the Director of the Ministry of Civil Defence & Emergency Management John Hamilton as National Controller. CDEM were supported by local authorities, New Zealand Police, Fire Service, Defence Force and many other agencies and organisations.

Gerry Brownlee, a Cabinet Minister, had his regular portfolios distributed amongst other cabinet ministers so that he could focus solely on earthquake recovery.

Establishment of Red Zone

A Central City Red Zone was established on the day of the earthquake as a public exclusion zone in central Christchurch. Both COGIC, French Civil Protection and the American USGS requested the activation of the International Charter on Space and Major Disasters on the behalf of MCDEM New Zealand, thus readily providing satellite imagery for aid and rescue services.

Police

Christchurch Police were supplemented by staff and resources from around the country, along with a 323-strong contingent of Australian Police, who were sworn in as New Zealand Police on their arrival, bringing the total number of officers in the city to 1200. Many of them received standing ovations from appreciative locals as they walked through Christchurch Airport upon arrival. Alongside regular duties, the police provided security cordons, organised evacuations, supported search and rescue teams, missing persons and family liaison, and organised media briefings and tours of the affected areas. They also provided forensic analysis and evidence gathering at fatalities and Disaster Victim Identification (DVI) teams, working closely with pathologists, forensic dentists and scientists, and the coroner at the emergency mortuary established at Burnham Military Camp. They were aided by DVI teams from Australia, UK, Thailand Taiwan and Israel.

Search and rescue

The New Zealand Fire Service coordinated search and rescue, with support from the Urban Search and Rescue (USAR) teams from New Zealand, Australia, United Kingdom, United States, Japan, Taiwan, China and Singapore, totalling 150 personnel from New Zealand and 429 from overseas. They also responded to fires, serious structural damage reports, and landslides working with structural engineers, seismologists and geologists, as well as construction workers, crane and digger operators and demolition experts.

NSW Task Force 1, a team of 72 urban search and rescue specialists from New South Wales, Australia was sent to Christchurch on two RAAF C-130J Hercules, arriving 12 hours after the quake. A second team of 70 from Queensland, Queensland Task Force 1, (including three sniffer dogs), was sent the following day on board a RAAF C-17 . A team of 55 Disaster Assistance and Rescue Team members from the Singapore Civil Defence Force were sent. The United States sent Urban Search and Rescue California Task Force 2, a 74-member heavy rescue team consisting of firefighters and paramedics from the Los Angeles County Fire Department, doctors, engineers and 26 tons of pre-packaged rescue equipment.
Japan sent 70 search-and-rescue personnel including specialists from the coastguard, police and fire fighting service, as well as three sniffer dogs. The team left New Zealand earlier than planned due to the 9.0 earthquake which struck Japan on 11 March 2011. The United Kingdom sent a 53 strong search and rescue team including nine Welsh firefighters who had assisted the rescue effort during the 2010 Haiti earthquake. Taiwan sent a 22-member team from the National Fire Agency, along with two tons of specialist search and rescue equipment. China sent a 10-member specialist rescue team.

Defence forces

The New Zealand Defence Force—staging their largest-ever operation on New Zealand soil— provided logistics, equipment, transport, airbridges, evacuations, supply and equipment shipments, survey of the Port and harbour, and support to the agencies, including meals; they assisted the Police with security, and provided humanitarian aid particularly to Lyttelton, which was isolated from the city in the first days. Over 1400 Army, Navy and Air Force personnel were involved, and Territorials (Army Reserve) were called up. They were supplemented by 116 soldiers from the Singapore Army, in Christchurch for a training exercise at the time of the earthquake, who assisted in the cordon of the city.

The Royal New Zealand Air Force provided an air bridge between Christchurch and Wellington using two Boeing 757 and three C-130 Hercules, and bringing in emergency crews and equipment and evacuating North Island residents and tourists out of Christchurch. One P-3 Orion