Ground motion modelling of an Alpine fault earthquake and a Hope fault earthquake for main South Island cities (NZ)

Executive Summary

The large September 2010 and the tragic February 2011 Canterbury earthquakes caused widespread damage by ground shaking and sand liquefaction in the Canterbury region. Both earthquakes were less than 50km from the Christchurch central business area and had a magnitude that is much smaller than that expected from the alpine Fault (Mw=8.2) and that is similar to a potential Hope fault event (Mw7+). At present, the response spectra from a great scenario earthquake from the alpine fault can only be estimated from ground-motion prediction equations (GMPEs) based on local and overseas earthquake records. A major problem of all GMPEs, including even the latest GMPEs from the next generation attenuation (NGA), for example, Abrahamson and Silva (2008), is their very large variability in ground motion predictions for large and great earthquakes.

Recent advances in earthquake mechanics allow us to compute seismograms for realistic earthquake scenarios, at specific locations, and with specific site conditions. Such simulations can provide very useful alternative estimates of possible ground motions from large faults for major population centres. In this study, instead of using GMPE, we carry out synthetic broadband simulations to derive synthetic strong-motion records.