2005 – Ground-Motion Attenuation Modelling in Australia; Implications for Earthquake Hazard and Ris

Trevor Allen, Phil R. Cummins, Trevor Dhu, John Schneider

Ground-motion attenuation models have been derived for the Australian crust. These models
employ both empirical and stochastic methods and are the first spectral ground-motion models to be
based entirely on Australian ground-motion data. In the past, these studies have been hampered by a lack of quality ground-motion data given Australia’s relatively low levels of seismicity.

Two key datasets have been employed to derive empirical ground-motion attenuation models for
Australia; one from data recorded in the Palaeozoic crust of southeastern Australia (SEA) and the
other from the Archean shield region of southwestern Western Australia (WA). Empirical ground motion models are derived for each of these datasets. In general, long-period (e.g. 1 sec) ground motion energy appears to attenuate less in WA than in SEA. These empirical models suggest that SEA has similar near-source attenuation with eastern North America. Because of the limited and spatially clustered nature of the WA dataset, however, we could not constrain attenuation models as well as in SEA.

Stochastic methods are employed to simulate ground-motions for larger earthquakes in regions
where recordings from real events are not available. These models are largely based upon source and attenuation parameters derived from empirical studies. Stochastic models are derived for SEA only.

Spectral ground-motion predicted by these models are generally lower than ground-motion predicted
by both eastern and western North American models, particularly at short-periods (T < 0.5 sec).
Results from this study have significant implications for earthquake hazard and risk in Australia. They
suggest that we are currently overestimating earthquake hazard in SEA. Furthermore, they suggest
that we cannot simply rely on North American ground-motion models to predict earthquake ground
motions in Australia.

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