Liquefaction impacts in residential areas in the 2010-2011 Christchurch ea…

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.

Question Time for 4 April 2012

Audio, Radio New Zealand

TODD McCLAY to the Minister of Finance: What recent reports has he received on the Government’s financial position? Dr RUSSEL NORMAN to the Prime Minister: Does he stand by his statement that “if you go and have a look at the tax cuts, they literally were neutral” and, if so, what is the projected net cost of the first four years of the 2010 tax package? DAVID SHEARER to the Prime Minister: Does he have confidence in all his Ministers? Dr PAUL HUTCHISON to the Associate Minister of Health: How will young New Zealanders receive better mental health services under the new Government package announced by the Prime Minister today? Hon DAVID PARKER to the Minister for Land Information: Has he or any other Minister this week sought further information on Shanghai Pengxin’s application for his approval to buy the Crafar farms, and if so, is it coincidence or purpose that this will further delay his decision on the application? NIKKI KAYE to the Minister of Education: What initiatives is she introducing to help schools tackle youth mental health? JULIE ANNE GENTER to the Minister of Transport: Has the Government reviewed its highway building programme in light of the warning in the briefing to the incoming Minister that there will be a $4.9 billion funding shortfall if oil prices remain high and economic growth remains low; if not, why not? CHARLES CHAUVEL to the Minister of Justice: Does she stand by all the answers she has given to questions asked of her to date? NICKY WAGNER to the Minister for Economic Development: What action has the Government taken to contribute to the recovery of high-tech businesses in Christchurch? Hon LIANNE DALZIEL to the Minister for Canterbury Earthquake Recovery: When will he approve a Recovery Plan for Christchurch’s CBD in light of the Christchurch City Council’s announcement that it will commence its Annual Plan processes next week? Rt Hon WINSTON PETERS to the Prime Minister: Does he have confidence in the Overseas Investment Office and his Ministers, Hon Jonathan Coleman and Hon Maurice Williamson over the issue of the latest Crafar farms deal; if so, why? CLARE CURRAN to the Prime Minister: What did he mean when he told the NZ Herald and other media last week that “We are comfortable with the current arrangements we have” with regards to Chinese telco Huawei’s involvement in our national broadband infrastructure, given that Australian Prime Minister Julia Gillard also said last week that “We’ve taken a decision in the national interest” to ban Huawei from even tendering for its broadband network? Questions to Members Hon DAVID PARKER to the Chairperson of the Finance and Expenditure Committee: Is it his intention to call the Treasury to appear before the committee to comment on the Report from the Controller and Auditor-General on The Treasury: Implementing and managing the Crown Retail Deposit Guarantee Scheme; if not, why not?