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Christchurch CBDAvon RiverHeathcote RiverChristchurch Cathedral▲▲Figure 3. Liquefaction documentation map of eastern Christchurch from drive-through reconnaissance.TABLE 1Geometric mean PGAs and adjusted cyclic stress ratios to M w = 7.5 earthquake (CSR 7.5 ) for four strong motion stationswithin/close to CBD, for five earthquakes in the period September 2010–June 2011Geometric Mean PGA (g) Cyclic Stress Ratio CSR*7.5Magnitude ScalingEventCBGS CCCC CHHC REHS CBGS CCCC CHHC REHS Factor MSF †4 SEP 10, M w = 7.1 0.158 0.224 0.173 0.252 0.089 0.127 0.098 0.142 1.1526 DEC 10, M w = 4.8 0.270 0.227 0.162 0.245 0.097 0.082 0.058 0.088 1.8022 FEB 11, M w = 6.2 0.501 0.429 0.366 0.522 0.199 0.170 0.145 0.208 1.6313 JUN 11, M w = 5.3 0.183 – 0.199 0.188 0.066 – 0.072 0.068 1.8013 JUN 11, M w = 6.0 0.163 – 0.215 0.264 0.060 – 0.079 0.097 1.77* CSR 7.5 = 0.65 (PGA/g)/MSF (at depth of groundwater)† MSF = 10 2.24 / M2.56w ≤ 1.8 (corresponding to the lower bound range recommended in Youd et al. 2001, with a cap of 1.8)]severity of its manifestation across Christchurch. The drivethroughsurvey aimed at capturing surface evidence of liquefactionas quickly as possible and quantifying its severity in aconsistent and systematic manner. The resulting liquefactiondocumentation map is shown in Figure 3. Three areas of differentliquefaction severity are indicated: A) moderate to severeliquefaction (black zone), B) low to moderate liquefaction (darkgray zone), and C) liquefaction predominantly on roads withsome on properties (light gray zone). Traces of liquefactionwere also observed in other areas. The suburbs to the east of theCBD along the Avon River (Avonside, Dallington, Avondale,Burwood, and Bexley) were most severely affected by liquefaction.About 5,000 residential properties in these suburbs willbe abandoned (New Zealand Government 2011). There wasalso substantial damage in areas of the CBD, and many heavilydamaged structures will require retrofit or demolition.Ten days after the earthquake, after the urban search andrescue efforts had largely finished, the authors initiated a comprehensiveground survey within the CBD to document liquefactioneffects in this area. Figure 4 shows a preliminary liquefactiondocumentation map for the CBD. This paper focusesprimarily on key observations of building performance withinthe principal liquefied zone stretching west-east through theCBD, from Hagley Park to the west, along the Avon River tothe northeast boundary of the CBD at the Fitzgerald Bridge.This zone is of particular interest because many high-risebuildings on shallow foundations and deep foundations wereaffected by the liquefaction in different ways.Even though the map shown in Figure 4 distinguishes thezone most significantly affected by liquefaction, the severity ofliquefaction within this zone was not uniform. The manifestationof liquefaction was primarily of moderate intensity with896 Seismological Research Letters Volume 82, Number 6 November/December 2011