ASSESSMENT OF ROCKFALL IMPACTS ON BUILDINGS DURING THE 2010-2011 CANTERBURY, NEW ZEALAND EARTHQUAKE SEQUENCE

Rock-slope failures during the 2010-2011 Canterbury (Christchurch), New Zealand Earthquake Sequence caused 5 fatalities and resulted in an estimated US$400 million of damage to buildings and infrastructure. Here we present a study if over 30 structures impacted by seismically induced rock fall in the Port Hills region of Christchurch, New Zealand. The consequences of rockfall impacts on structures, taken as both penetration distance into structures and building damage footprint, are shown to follow a power-law distribution with impact energy. Detailed mapping of rock fall sources and paths from field mapping, aerial lidar digital elevation model (DEM) data, and high-resolution aerial imagery provided well-constrained runout paths of boulders. Lumped mass, two-dimensional rock fall runout models were used with high resolution (1-m or better) lidar elevation data to estimate boulder impact velocities and energies. The boulder run out models were based on calibrated surface parameters from mapped runout paths of ~200 additional rock fall runouts. Terrestrial lidar scans generated 3-D point cloud data used to measure structural damage and impacting boulders. The case histories and resulting fragility curves serve as a quantitative basis for risk assessment of rock fall hazards by linking vulnerability data to the predicted impact energies from the hazard analysis.