GIS modelling in support of earthquake-induced rockfall and cliff collapse risk assessment in the Port Hills, Christchurch.

Ground shaking associated with the 22 February 2011 Mw6.2 Christchurch earthquake exceeded MM10 and dislodged boulders from cliffs on the upper slopes of the Port Hills, southeast of Christchurch City. Boulders rolled into the urban areas below. Cliffs on the lower slopes collapsed and debris avalanches inundated homes built at their bases and undercut homes built at their crests. Boulders and debris avalanches impacted over 200 buildings and killed five people, resulting in widespread evacuations. Large aftershocks caused further boulder rolls and cliff collapses. Before buildings could be reoccupied a life-safety risk assessment was required. This study included pilot investigations of the 19 worst affected areas and these were used to develop hazard and risk models. Once ground verified, the models were extended to the entire Port Hills area. GIS was the main tool used in the development of the models, but other tools and techniques were also utilised. [ABSTRACT FROM AUTHOR]