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(A)(B)(C)▲▲Figure 15. Bridges with damage not associated with liquefaction: A) Moorhouse Avenue, B) Port Hills, C) Horotane.east direction (Figure 2). Shown in Figure 15C, the bridge is adual three-span reinforced concrete bridge supported by singlepier bents. The end spans are supported by seat-type abutments,with the structure spanning between two large builtupembankments approximately 9 m high. The embankmentslopes beneath the abutments and parallel to the roadway havean angle of about 33° relative to the horizontal (i.e., 1.5H:1Vslope). This bridge is ~200 m from the Port Hills Overbridge,and had also been recently retrofitted using a similar approach,with abutment seat extensions and linkages between the bridgeelements.This bridge did not suffer any damage during the Darfieldearthquake. During the Christchurch earthquake, the retrofitmethod appeared to have worked well in terms of protectingthe structure. The ties between spans and at the abutmentselongated and pulled out, as they had in the Port HillsOverbridge. Additionally, 60% of the bolts that attached thesoffit of the precast concrete beams to the abutment seat extensionhad sheared off.The northwest abutment back-rotated 1° and a transversecrack developed at the top of the northwest slope near theconcrete abutment; however, this was not continuous acrossthe slope. The southeast abutment back-rotated by 3.4°and atransverse crack developed at the bottom of the slope on thenortheast side. A significant transverse crack 10 cm wide and60 cm deep opened up at the top of the southeast slope and wascontinuous across the width of the bridge. A transverse scarpalso developed near the toe of the 13-m-long slope, extendingbetween the southern piers of the two bridges, suggesting thata slope failure had been initiated in the embankment fill butdid not become unstable. Movement was also evident perpendicularto the bridge axis, with cracking in the slope extendingthrough the abutment, resulting in wide cracking and lateralmovement of the abutment and superstructure (Figure 17).CONCLUSIONS▲▲Figure 16. Moorhouse Avenue Overbridge pier flexural bucklingfailure.Overall, the bridges in Christchurch and the Canterburyregion performed well during the Darfield and Christchurchearthquakes, given the magnitude of the observed groundmotions. Of those bridges that were damaged, the majoritywere as a result of liquefaction-induced lateral spreading, withonly four bridges suffering damage not related to liquefactioneffects. Even though the larger-magnitude Darfield eventaffected a much wider region, the location of the Christchurchevent resulted in more significant damage due to the intensityof shaking in a region of the city with many bridges and highliquefaction susceptibility.As a result of the significant lateral spreading, the mostaffected components of the bridges were the approaches, abutments,piers, and foundation system. Bridges were able to resistthe inertial forces due to shaking, while the compressive lateralspreading forces resulted in abutment rotation and foundationdamage. For almost all cases the predicted and observed lique-962 Seismological Research Letters Volume 82, Number 6 November/December 2011