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Research papers, University of Canterbury Library

In the period between September 2010 and December 2011, Christchurch (New Zealand) and its surroundings were hit by a series of strong earthquakes including six significant events, all generated by local faults in proximity to the city: 4 September 2010 (Mw=7.1), 22 February 2011 (Mw=6.2), 13 June 2011 (Mw=5.3 and Mw=6.0) and 23 December 2011 (M=5.8 and (M=5.9) earthquakes. As shown in Figure 1, the causative faults of the earthquakes were very close to or within the city boundaries thus generating very strong ground motions and causing tremendous damage throughout the city. Christchurch is shown as a lighter colour area, and its Central Business District (CBD) is marked with a white square area in the figure. Note that the sequence of earthquakes started to the west of the city and then propagated to the south, south-east and east of the city through a set of separate but apparently interacting faults. Because of their strength and proximity to the city, the earthquakes caused tremendous physical damage and impacts on the people, natural and built environments of Christchurch. The 22 February 2011 earthquake was particularly devastating. The ground motions generated by this earthquake were intense and in many parts of Christchurch substantially above the ground motions used to design the buildings in Christchurch. The earthquake caused 182 fatalities, collapse of two multi-storey reinforced concrete buildings, collapse or partial collapse of many unreinforced masonry structures including the historic Christchurch Cathedral. The Central Business District (CBD) of Christchurch, which is the central heart of the city just east of Hagley Park, was practically lost with majority of its 3,000 buildings being damaged beyond repair. Widespread liquefaction in the suburbs of Christchurch, as well as rock falls and slope/cliff instabilities in the Port Hills affected tens of thousands of residential buildings and properties, and shattered the lifelines and infrastructure over approximately one third of the city area. The total economic loss caused by the 2010-2011 Christchurch earthquakes is currently estimated to be in the range between 25 and 30 billion NZ dollars (or 15% to 18% of New Zealand’s GDP). After each major earthquake, comprehensive field investigations and inspections were conducted to document the liquefaction-induced land damage, lateral spreading displacements and their impacts on buildings and infrastructure. In addition, the ground motions produced by the earthquakes were recorded by approximately 15 strong motion stations within (close to) the city boundaries providing and impressive wealth of data, records and observations of the performance of ground and various types of structures during this unusual sequence of strong local earthquakes affecting a city. This paper discusses the liquefaction in residential areas and focuses on its impacts on dwellings (residential houses) and potable water system in the Christchurch suburbs. The ground conditions of Christchurch including the depositional history of soils, their composition, age and groundwater regime are first discussed. Detailed liquefaction maps illustrating the extent and severity of liquefaction across Christchurch triggered by the sequence of earthquakes including multiple episodes of severe re-liquefaction are next presented. Characteristic liquefaction-induced damage to residential houses is then described focussing on the performance of typical house foundations in areas affected by liquefaction. Liquefaction impacts on the potable water system of Christchurch is also briefly summarized including correlation between the damage to the system, liquefaction severity, and the performance of different pipe materials. Finally, the characteristics of Christchurch liquefaction and its impacts on built environment are discussed in relation to the liquefaction-induced damage in Japan during the 11 March 2011 Great East Japan Earthquake.

Research papers, University of Canterbury Library

The 22 February 2011, Mw6.2 Christchurch earthquake is the most costly earthquake to affect New Zealand, causing an estimated 181 fatalities and severely damaging thousands of residential and commercial buildings. This paper presents a summary of some of the observations made by the NSF-sponsored GEER Team regarding the geotechnical/geologic aspects of this earthquake. The Team focused on documenting the occurrence and severity of liquefaction and lateral spreading, performance of building and bridge foundations, buried pipelines and levees, and significant rockfalls and landslides. Liquefaction was pervasive and caused extensive damage to residential properties, water and wastewater networks, high-rise buildings, and bridges. Entire neighborhoods subsided, resulting in flooding that caused further damage. Additionally, liquefaction and lateral spreading resulted in damage to bridges and to stretches of levees along the Waimakariri and Kaiapoi Rivers. Rockfalls and landslides in the Port Hills damaged several homes and caused several fatalities.

Images, UC QuakeStudies

Warning tape on the gate of a residential property near Cranmer Square. The photographer comments, "The yellow tape was put on the gate to warn property [owners] that the house beyond was unsafe. Now there is no house, but by the cobwebs on the handle the tape is doing a great job".

Images, UC QuakeStudies

A photograph captioned by BeckerFraserPhotos, "This photo epitomises aspects of many homes in the residential red zone. A home that used to be lovely once upon a time, and now is just a broken house, with indicators of the care once lavished upon it by the family that owned it in the rose bush still flowering by the door. Seabreeze Close, Bexley".

Videos, UC QuakeStudies

A video of interviews with three residents about their Port Hills properties. The video was filmed the day after Earthquake Recovery Minister Gerry Brownlee announced the red-zoning of 285 Port Hills properties. The video includes an interview with Marine Kent (whose house was zoned white to green), Mark Tranter (whose house was zoned white to red), and Tony Ging (whose house is still white-zoned).

Images, UC QuakeStudies

Liquefaction in a residential property in North New Brighton. The fence has subsided into the silt, and a temporary water line runs along the street in front. The photographer comments, "Because this is in the Christchurch red zone the people living here, if they have lost one of the normal essentials such as sewage they will not get it repaired. It is get out or live in third world conditions. The blue line is the temporary water pipe, which will be removed when the area is depopulated".

Images, UC QuakeStudies

A residential street in New Brighton. Liquefaction still lines the street, and lampposts are leaning in different directions. The photographer comments, "This is the New Brighton red zone, which is parallel to the Avon River. The area suffered serious liquefaction during the numerous earthquakes/aftershocks and the land is being bought by the government. Although the houses do not look too bad in the background they have suffered badly. On the day I took this picture the council had just hours before cut the grass, which made the area look less abandoned".