Christchurch New Zealand 2011 (GNS)
On Tuesday February 22, 2011, at 12.51 pm local time, an earthquake of moment magnitude (Mw) 6.1 and focal depth 5 km struck the Canterbury Region, in New Zealand’s South Island. The epicenter (43.583 S, 172.68 E) was around 10 km south-east of Christchurch City (367,700 inhabitants), near the port of Lyttleton.
This event is considered to be part of the aftershock sequence of the September 4, 2010 Darfield earthquake involving oblique-thrust faulting at the easternmost limit of previous aftershocks.
The proximity of the rupture (about 14km of subsurface rupture, GNS Science), and the shallow focal depth combined with the fact that much of the damage in Christchurch remained unrepaired since the September 2010 earthquake and following aftershocks have made the February 22, 2011 earthquake surprisingly devastating and damaging for its magnitude.
The earthquake produced exceptionally high values of ground shaking up to 2.2 g (vertical component) with another two readings beyond 1 g, and maximum intensity of MM IX-X. Extensive slope failures (landslides and rock falls) and liquefaction occurred.
1 Population at June 2011. New Zealand Statistics http://www.stats.govt.nz/
Hardest hit was the city of Christchurch, especially the Central Business District (CBD) and its southern and eastern suburbs. The city is built on former swamps with coarser gravel deposits more common in the western part, and finer-grained sediment, such as sand, silt and clay in the eastern part close to the coast, the latter having a shallow groundwater level (0-2m).
Liquefaction was much more extensive and severe than in September’s earthquake causing higher extent of damage to buildings and to the lifeline systems of the city (in particular water and wastewater pipes). Roads and bridges were also damaged as effect of ground settlement and lateral spreading.
In general, the most significant damage to lifelines and residential buildings was due to liquefaction. Liquefaction phenomena resulted in widespread ejection of silt and fine sand (some of which contaminated by raw sewage) that created a significant demand in resources and time. Despite damage to homes, there were few serious injuries in residential houses in liquefaction areas.
The Port Hills area, built on volcanic rocks, experienced extensive rockfalls and rock slope failures leading to tens of houses being impacted by falling rocks (four people were killed by falling rocks).
91% of the city’s 190000 dwellings suffered damage due to the earthquake, 7860 (as of April 8, 2013) of these were marked for demolition and another 9,000 (excluding the red zone) were made uninhabitable (CERA, 2012). Over 1200 commercial and public buildings (including 212 heritage buildings) were also slated for full or partial demolition, of which 900 were in the CBD.
The earthquake killed 185 people: 115 people died due to the collapse of the CBD building and 18 due to the collapse of the PGC building. In addition 36 people were killed (mostly due to falling masonry) in the city’s CBD and another 12 in the suburbs (incl. 5 due to rockfalls). The remaining 4 fatalities were subsequently associated to the earthquake by the Chief Coroner since their death was caused by injuries suffered during the earthquake. The Accident Compensation Corporation received 7133 quake-related injury claims.
The earthquake had a huge economic impact with the overall direct economic loss estimated at 15-16 billion USD by SwissRe and MunichRe, respectively (9.5-10% of New Zealand’s GDP in 2011). Most of these losses are insured losses that are expected to reach 12-13 billion USD (SwissRe, MunichRe respectively).
EQC’s insurance payouts as of November 3, 2013 reached 6.32 billion NZD (5.23 billion USD) incl. claims for the whole Canterbury earthquake sequence (from September 4, 2010) with 57.6% of 744,248 accepted claims having been closed. EQC’s current projection (Nov. 3, 2013) is that the total payouts will reach 12 bilion NZD (9.96 billion USD).
2 TeAra, Encyclopedia of NZ http://www.teara.govt.nz/en/historic-earthquakes/page-13.
3 CERA. Environment Canterbury Preliminary Draft Land Use Recovery Plan (2013), at 36.
Based on ACC Press Releases on April 8, 2011 there were 7133 injury claims, but it is not clear if the lists contained double counting due to multiple injuries per person as the data were by type of injury. The ACC estimated that 6659 people were injured in the first 24h (Ardagh et al., 2012. The initial health-system response to the earthquake in Christchurch, New Zealand, in February, 2011. Lancet 2012; 379, pp. 2109–15. DOI:10.1016/S0140-6736(12)60313-4).
115 people incl. 4 unidentified people died in the Canterbury Television (CTV) building; 18 people died in the Pyne Gould Corporation (PGC) building; 8 people died on a bus crushed by falling masonry in the CBD; 28 people died in other areas of the CBD; 12 people died in suburban locations. 4 fatalities were subsequently associated to the earthquake by the Chief Coroner since their death was caused by injuries suffered during the earthquake.
133 (74%) killed by the collapse of two mid-rise reinforced concrete office buildings.
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 (one of which during an aftershock).
Severe damage or collapse of buildings was induced by ground shaking (in the CBD) and liquefaction (in the suburbs of Christchurch). During the mainshock in the CBD: 710 (24%) red-tag buildings, plus 50 (1.7%) at risk from adjacent buildings. In the aftermath of the June 13, 2011 aftershock another 29 red-tag buildings, as well as 18 more at risk from adjacent stuctures (total 807 buildings or 27.2%).
Eventually when all surveys were completed there were 1,199 buildings (1,042 & 157 to be completely or partially demolished) in the CERA list of critical buildings (incl. non-residential). The list refers to cumulative damage during the whole 2010-12 Canterbury earthquakes sequence, incl. the effects of liquefaction.
In addition 7,779 houses in the liquefaction affected areas will be demolished under the Voluntary Crown Offer scheme (a system allowing families to relocate in new areas, safe from liquefaction hazard). Some double-counting may occur between the CERA and the Voluntary Crown Offer lists. Furthermore commercial buildings, vacant buildimgs and uninsured land owners in the residential red zone are not included in these figures.
According to the EQC, approximately 141,000 building damage claims were accepted that were solely related to the February 22, 2011 earthquake. Claims refer to individual properties (not buildings).
Approximately 5,000 out of 13,000 commercial and industrial buildings were damaged (Platt, S., 2012, Reconstruction in New Zealand Post 2010-11 Christchurch Eearthquakes, ReBuilDD Field Trip February 2012).
Of around 190,000 dwellings in Greater Christcurch about 91% were damaged (incl. those that were destroyed), about 110,000 Christchurch dwellings requiring major repairs, another 60,000 dwellings requiring smaller repairs (http://beckerfraserphotos.co.nz/post/46307415988/why-is-it-taking-so-lon...).
According to the EQC as of March 10, 2012, 156,590 building damage claims were accepted that were solely related to the February 22, 2011 earthquake.
According to an analysis of cellphone calls made by Christchurch users, around 55,000 residents may have left the city in the week after the February 2011 earthquake (CERA, 2013).
About 10,000 households displaced (http://www.oceanpartners.co.nz/earthquakes/)
16 billion US$ overall economic loss incl. 13 billion in insured losses (Munich Re).
Estimated indirect losses due to the entire 2010-2012 Canterbury earthquakes sequence mostly due to GDP loss in Canterbury and temporary relocation costs for homes and businesses.
By February 23, 2012 (one year anniversary) the EQC had paid 1.315 billion US$ in claims with 15.5% of the claims closed, while 36% had not yet received any payment. These losses refer only to claims (buildings, contents, land) related to the February 22, 2011 Christchurch earthquake.
Estimate of the total number of buildings in the greater Christchurch area.
Approximately 13,000 commercial and industrial buildings (Platt, S., 2012, Reconstruction in New Zealand Post 2010-11 Christchurch Eearthquakes, ReBuilDD Field Trip February 2012).