Located on the edge of two tectonic plates, New Zealand has numerous fault lines and seismic risk across the whole country. The way this risk is communicated affects whether people prepare effectively or at all. Research has shown that perceptions of risk are affected by slight changes in wording, and that probabilities commonly reported by experts and media are often interpreted subjectively based on context. In the context of volcanoes, research has found that given a certain probability of a volcano in a specific time window, people perceive risk as higher in later time intervals within that window. The present study examines this pattern with regard to earthquakes and aftershocks in the New Zealand context. Participants in both Wellington (N = 102) and Christchurch (N = 98) were presented an expert statement of earthquake risk within a given time window in Wellington and aftershock risk in Christchurch, and asked to rate their perception of risk in specific intervals across the time window. For a Wellington earthquake, participants perceived risk as incrementally higher toward the end of the 50 year time window whereas for a Christchurch aftershock, risk perception increased slightly for the first three intervals of the 12 month time window. Likelihood of preparing was constant over the time windows, with Wellington citizens rating themselves more likely than Christchurch citizens to prepare for either an earthquake or aftershock, irrespective of current level of preparedness. These findings suggest that people view earthquakes as more likely later toward the end of a given time window and that they view aftershocks very differently to scientific predictions.
When the devastating 6.3 magnitude earthquake hit Christchurch, Aotearoa New Zealand, at 12.51pm on 22nd February 2011, the psychological and physical landscape was irrevocably changed. In the days and weeks following the disaster communities were isolated due to failed infrastructure, continuing aftershocks and the extensive search and rescue effort which focussed resources on the central business district. In such moments the resilience of a community is truly tested. This research discusses the role of grassroots community groups in facilitating community resilience during the Christchurch 2010/11 earthquakes and the role of place in doing so. I argue that place specific strategies for urban resilience need to be enacted from a grassroots level while being supported by broader policies and agencies. Using a case study of Project Lyttelton – a group aspiring towards a resilient sustainable future who were caught at the epicentre of the February earthquake – I demonstrate the role of a community group in creating resilience through self-organised place specific action during a disaster. The group provided emotional care, basic facilities and rebuilding assistance to the residents of Lyttelton, proving to be an invaluable asset. These actions are closely linked to the characteristics of social support and social learning that have been identified as important to socio-ecological resilience. In addition this research will seek to understand and explore the nuances of place and identity and its role in shaping resilience to such dis-placing events. Drawing on community narratives of the displacement of place identity, the potential for a progressive sense of place as instigated by local groups will be investigated as an avenue for adaptation by communities at risk of disaster and place destabilisation.
The Mѡ=7.1 Darfield (Canterbury) earthquake struck on 4 September 2010, approximately 45 km west of Christchurch, New Zealand. It revealed a previously unknown fault (the Greendale fault) and caused billions of dollars of damage due to high peak ground velocities and extensive liquefaction. It also triggered the Mw=6.3 Christchurch earthquake on 22 February 2011, which caused further damage and the loss of 185 lives. The objective of this research was to determine the relationship between stress and seismic properties in a seismically active region using manually-picked P and S wave arrival times from the aftershock sequence between 8 September 2010-13 January 2011 to estimate shear-wave splitting (SWS) parameters, VP =VS-ratios, anisotropy (delay-time tomography), focal mechanisms, and tectonic stress on the Canterbury plains. The maximum horizontal stress direction was highly consistent in the plains, with an average value of SHmax=116 18 . However, the estimates showed variation in SHmax near the fault, with one estimate rotating by as much as 30° counter-clockwise. This suggests heterogeneity of stress at the fault, though the cause remains unclear. Orientations of the principal stresses predominantly indicate a strike-slip regime, but there are possible thrust regimes to the west and north/east of the fault. The SWS fast directions (ø) on the plains show alignment with SHmax at the majority of stations, indicating stress controlled anisotropy. However, structural effects appear more dominant in the neighbouring regions of the Southern Alps and Banks Peninsula.
Measurement of basement seismic resonance frequencies can elucidate shallow velocity structure, an important factor in earthquake hazard estimation. Ambient noise cross correlation, which is well-suited to studying shallow earth structure, is commonly used to analyze fundamental-mode Rayleigh waves and, increasingly, Love waves. Here we show via multicomponent ambient noise cross correlation that the basement resonance frequency in the Canterbury region of New Zealand can be straightforwardly determined based on the horizontal to vertical amplitude ratio (H/V ratio) of the first higher-mode Rayleigh waves. At periods of 1-3 s, the first higher-mode is evident on the radial-radial cross-correlation functions but almost absent in the vertical-vertical cross-correlation functions, implying longitudinal motion and a high H/V ratio. A one-dimensional regional velocity model incorporating a ~ 1.5 km-thick sedimentary layer fits both the observed H/V ratio and Rayleigh wave group velocity. Similar analysis may enable resonance characteristics of other sedimentary basins to be determined. © 2013. American Geophysical Union. All Rights Reserved.
In the aftermath of the 2011 earthquake, a state of polycentric urbanity was thrust upon New Zealand’s second largest city. As the city-centre lay in disrepair, smaller centres started to materialise elsewhere, out of necessity. Transforming former urban peripheries and within existing suburbs into a collective, dispersed alternative to the city centre, these sub-centres prompted a range of morphological, socio-cultural and political transformations, and begged multiple questions: how to imbue these new sub-centres with gravity? How to render them a genuine alternative to the CBD? How do they operate within the wider city? How to cope with the physical and cultural transformations of this shifting urbanscape and prevent them occurring ad lib? Indeed, the success and functioning of the larger urban structure hinges upon a critical, informed response to these sub-centre urban contexts. Yet, with an unrelenting focus on the CBD rebuild - effectively a polycentric denial - little such attention has been granted. Taking this urban condition as its premise and its provocation, this thesis investigates architecture’s role in the emergent sub-centre. It asks: what can architecture do in these urban contexts; how can architecture act upon the emergent sub-centre in a critical, catalytic fashion? Identifying this volatile condition as both an opportunity for architectural experimentation and a need for critical architectural engagement, this thesis seeks to explore the sub-centre (as an idea and actual urban context) as architecture’s project: its raison d’etre, impetus and aspiration. These inquiries are tested through design-led research: an initial design question provoking further, broader discursive research (and indeed, seeking broader implications). The first section is a site-specific, design for Sumner, Christchurch. Titled ‘An Agora Anew’; this project - both in conception and outcome - is a speculative response to a specific sub-centre condition. The second section ‘The Sub-centre as Architecture’s Project’ explores the ideas provoked by the design project within a discursive framework. Firstly it identifies the sub-centre as a context in desperate need of architectural attention (why architecture?); secondly, it negotiates a possible agenda for architecture in this context through terms of engagement that are formal, critical and opportunistic (how architecture?): enabling it to take a position on and in the sub-centre. Lastly, a critical exegesis positions the design in regards to the broader discursive debate: critiquing it an architectural project predicated upon the idea of the sub-centre. The implications of this design-led thesis are twofold: firstly, for architecture’s role in the sub-centre (especially to Christchurch); secondly for the possibilities of architecture’s productive engagement with the city (largely through architectural form), more generally. In a century where radical, new urban contexts (of which the sub-centre is just one) are commonplace, this type of thinking – what can architecture do in the city? - is imperative.
