Engineers Australia

Earthquake-induced landsliding in New Zealand and potential for landslides during earthquakes in Adelaide, South Australia

Graham T Hancox

Abstract

A study of landsliding caused by historical earthquakes in New Zealand was completed at the end of 1997. That study showed the minimum magnitude for earthquake-induced landsliding (EIL) in N.Z. to be M 5, with significant landsliding at M 6 or greater. The minimum MM intensity for landsliding is MM6 and the most common intensities for landslides are MM7–8. The threshold for liquefaction is MM7 for sand boils and MM8 for lateral spreading. Environmental criteria (landslides, liquefaction) were also defined for the MM Intensity Scale.

In this paper the EIL relationships and MM Intensity criteria are described and then applied in Adelaide. This indicates that an M 6–7 (MM8–9) earthquake in the Adelaide area could cause moderate to large rock falls and slides on high unsupported cuts, river banks, terrace edges and coastal cliffs. Liquefaction damage could also occur in areas of saturated sandy alluvium and estuarine deposits. The historical seismic record, however, suggests that the probability of an M 6 or M 7 earthquake in Adelaide is relatively low; hence the potential risk from earthquake-induced landslides and liquefaction is also likely to be low.