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Soil Liquefaction Effects in the CentralBusiness District during the February 2011Christchurch EarthquakeMisko Cubrinovski, Jonathan D. Bray, Merrick Taylor, Simona Giorgini, Brendon Bradley, Liam Wotherspoon, and Joshua ZupanMisko Cubrinovski, 1 Jonathan D. Bray, 2 Merrick Taylor, 1 SimonaGiorgini, 1 Brendon Bradley, 1 Liam Wotherspoon, 3 and Joshua Zupan 2INTRODUCTIONDuring the period between September 2010 and June 2011,the city of Christchurch was strongly shaken by a series ofearthquakes that included the 4 September 2010 (M w = 7.1),26 December 2010 (M w = 4.8), 22 February 2011 (M w = 6.2),and 13 June 2011 (M w = 5.3 and M w = 6.0) earthquakes. Themoment magnitude (M w ) values adopted in this paper are takenfrom GNS Science, New Zealand (http://www.geonet.org.nz);they are 0.1 units higher than the corresponding M w valuesreported by the U.S. Geological Survey (http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usb0001igm/). Theseearthquakes produced strong ground motions within the centralbusiness district (CBD) of Christchurch, which is the centralheart of the city just east of Hagley Park and encompassesapproximately 200 ha. Some of the recorded ground motionshad 5% damped spectral accelerations that surpassed the 475-year return-period design motions by a factor of two. Groundshaking caused substantial damage to a large number of buildingsand significant ground failure in areas with liquefiablesoils. The 22 February earthquake was the most devastating.It caused 181 fatalities and widespread liquefaction and lateralspreading in the suburbs to the east of the CBD and in areaswithin the CBD, particularly along the stretch of the AvonRiver that runs through the city. There were pockets of heavydamage in the CBD, including the collapse of two multistoryreinforced concrete buildings, as well as the collapse and partialcollapse of many unreinforced masonry structures includingthe historic Christchurch Cathedral in the center of the CBD.Soil liquefaction in a substantial part of the CBD adverselyaffected the performance of many multistory buildings, resultingin global and differential settlements, lateral movement offoundations, tilt of buildings, and bearing failures.The M w = 6.2, 22 February 2011 earthquake is especiallymeaningful for earthquake professionals because it occurredjust five months after the M w = 7.1, 4 September 2010 Darfield1. University of Canterbury, Christchurch, New Zealand2. University of California, Berkeley, California, U.S.A.3. University of Auckland, Auckland, New Zealandearthquake, the epicenter of which was approximately 40 kmfrom the Christchurch CBD. Whereas the 22 February eventkilled almost two hundred people, the 4 September eventresulted in no deaths. Although the September event causedwidespread liquefaction-induced damage in the Christchurcharea, it did not cause significant liquefaction-induced damagewithin the CBD. There is much to learn from comparingthe different levels of soil liquefaction, differing magnitudesand seismic source distances, and variable performanceof buildings, lifelines, and engineered systems during thesetwo earthquakes. It is rare to have the opportunity to documentthe effects of one significant earthquake on a moderncity with good building codes. It is extremely rare to have theopportunity to learn how the same ground and infrastructureresponded to two significant earthquakes.This paper summarizes the key field observations madefollowing the 22 February 2011 Christchurch earthquakeregarding the effects of soil liquefaction on building performancein the CBD. Other papers in this special issue provideinformation on earthquake ground motions and the geotechnicaleffects of this event outside the CBD. Additionally, theeffects of the 4 September 2010 Darfield earthquake were documentedpreviously (e.g., Cubrinovski et al. 2010). After a briefoverview of the CBD, we describe the typical soil conditions inthe CBD, followed by a summary of recorded ground motionsin the CBD. There are several cases of buildings with differentfoundation types (e.g., isolated spread footings, spread footingswith grade beams, raft foundations, and pile foundations) thatperformed differently in liquefied ground. Representative casesof building performance on liquefied ground are described toprovide insights regarding the effects of soil liquefaction onurban areas with modern construction.CHRISTCHURCH CENTRAL BUSINESS DISTRICTChristchurch is situated in the middle part of the east coastof the South Island of New Zealand. It has a population ofabout 350,000 (the second-largest city in New Zealand). Itsurban area covers approximately 450 km 2 . It is sparsely developedwith approximately 150,000 dwellings (predominantlydoi: 10.1785/gssrl.82.6.893Seismological Research Letters Volume 82, Number 6 November/December 2011 893