Determining Rockfall Risk in Christchurch Using Rockfalls Triggered by the 2010–2011 Canterbury Earthquake Sequence

Abstract

The Canterbury earthquake sequence triggered thousands of rockfalls in the Port Hills of Christchurch, New Zealand, with over 6,000 falling on 22 February 2011. Several hundred families were evacuated after about 200 homes were hit. We characterized the rockfalls by boulder-size distribution, runout distance, source-area dimensions, and boulder-production rates over a range of triggering peak ground accelerations. Using these characteristics, a time-varying seismic hazard model for Canterbury, and estimates of residential occupancy rates and resident vulnerability, we estimated annual individual fatality risk from rockfall in the Port Hills. The results demonstrate the Port Hills rockfall risk is time-variable, decreasing as the seismic hazard decreases following the main earthquakes in February and June 2011. This presents a real challenge for formulating robust land-use and reconstruction policy in the Port Hills.

Strong proximal earthquakes revealed by cosmogenic 3He dating of prehistoric rockfalls, Christchurch, New Zealand

“…Five fatalities and significant infrastructural damage during the Christchurch I earthquake resulted from coseismic rockfall and cliff collapse (Bradley, 2013;Massey et al, 2014). Major rockfall also occurred in an M w 6.0 earthquake on 13 June 2011 (termed the Christchurch II-b earthquake) (Fig.…”

Optical dating of loessic hillslope sediments constrains timing of prehistoric rockfalls, Christchurch, New Zealand

“…These loess deposits host numerous palaeorockfall boulders that have previously been dated by cosmogenic 3 He (Mackey and Quigley, ), enabling cross‐validation of our optical ages with independent age control. The new luminescence ages allow us to refine the timing of palaeorockfall emplacement in an area of high rockfall hazard (Massey et al ., ). This study and that of Borella et al .…”

Stochastic ground motion modelling of the largestMw5.9 + aftershocks of the Canterbury 2010–2011 earthquake sequence

“…This study was initiated by the need to obtain realistic ground-motion characteristics at sites of interest for seismic slope-response analyses in the Port Hills (Christchurch) for the seismic response of slopes research project funded by New Zealand's Natural Hazard Platform (Holden & Kaiser 2014). None of these sites was equipped with a strong-motion sensor at the time of the Canterbury earthquakes; a preliminary approach was to use the nearest ground-motion recording or an average of the nearest recordings to assess slope damage (Massey et al 2012a(Massey et al , 2012b(Massey et al , 2014. Distances to the nearest site can be quite large however, and many of the sites exhibit strong local site effects that may bias ground motion estimates (e.g.…”