Rockfall at Port Hills, Christchurch. Credit: Rob Becker

One of the legacies of the Christchurch earthquake sequence in New Zealand has been both increased levels of rockfall hazard and increased awareness of the level of hazard that predated the seismic events.  The most seriously affected area is the Port Hills area to the southeast of the city, where large numbers of houses were affected by rockfalls during the earthquakes, and may more were left at risk in the aftermath.  To assess the level of hazard properly, Christchurch City Council commissioned GNS Science to undertake a quantitative life risk assessment for the affected areas.  This has been a huge piece of work, undertaken in the public spotlight on a very short timescale.  The aim has been to generate the best possible assessment of the risk to life; this assessment can then be used as the basis for decisions on the viability of individual properties.

Christchurch City Council have now released the full set of reports of the rockfall life risk assessment, such that they are available for download.  A total of seven reports are available as PDFs as follows:

  1. Canterbury Earthquakes 2010/2011 Port Hills Slope Stability: Geomorphology mapping for rockfall risk assessment
  2. Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Principles and criteria for the assessment of risk from slope instability in the Port Hills, Christchurch
  3. Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Pilot study for assessing life-safety risk from cliff collapse
  4. Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Life-safety risk from cliff collapse in the Port Hills
  5. Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Additional assessment of the life-safety risk from rockfalls (boulder rolls)
  6. Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Pilot study for assessing life-safety risk from rockfalls (boulder roll)
  7. Canterbury Earthquakes 2010/11 Port Hills Slope Stability: Life-safety risk from rockfalls (boulder roll) in the Port Hills
  8. Separate maps associated with the reports

The analysis presented in these reports is really fascinating – they are the most comprehensive, carefully considered and thorough rockfall risk assessments that I have ever seen.  I strongly commend in particular the “principles and criteria” report (number 2) and the Life safety risk reports (numbers 4 and 7).

Inevitably the political situation with regard to implementing the outcome of these analyses is very complex, but at least there is a credible scientific analysis from which to start.

Re-blogged from Dave Petley’s Landslide Blog – http://blogs.agu.org/landslideblog/

Prof Dave Petley is Wilson Chair in Hazard and Risk at the Institute of Hazard, Risk and Resilience.

Further Reading

The latest events in the Christchurch earthquake sequence

Christchurch earthquake secondary hazards

New Maps of christchurch earthquake

Images of landslides from the Christchurch earthquakes