ALBERT

Description: During the period between September 2010 and June 2011, the city of Christchurch was strongly shaken by a series of earthquakes that included the 4 September 2010 (Mw = 7.1), 26 December 2010 (Mw = 4.8), 22 February 2011 (Mw = 6.2), and 13 June 2011 (Mw = 5.3 and Mw = 6.0) earthquakes. The moment magnitude (Mw) values adopted in this paper are taken from GNS Science, New Zealand (http://www.geonet.org.nz); they are 0.1 units higher than the corresponding Mw values reported by the U.S. Geological Survey (http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usb0001igm/). These earthquakes produced strong ground motions within the central business district (CBD) of Christchurch, which is the central heart of the city just east of Hagley Park and encompasses approximately 200 ha. Some of the recorded ground motions had 5% damped spectral accelerations that surpassed the 475-year return-period design motions by a factor of two. Ground shaking caused substantial damage to a large number of buildings and significant ground failure in areas with liquefiable soils. The 22 February earthquake was the most devastating. It caused 181 fatalities and widespread liquefaction and lateral spreading in the suburbs to the east of the CBD and in areas within the CBD, particularly along the stretch of the Avon River that runs through the city. There were pockets of heavy damage in the CBD, including the collapse of two multistory reinforced concrete buildings, as well as the collapse and partial collapse of many unreinforced masonry structures including the historic Christchurch Cathedral in the center of the CBD. Soil liquefaction in a substantial part of the CBD adversely affected the performance of many multistory buildings, resulting in global and differential settlements, lateral movement of foundations, tilt of buildings, and bearing failures. The Mw = 6.2, 22 February 2011 earthquake...