2004 – Development Of Australian Ground-Motion Models For Engineering Design

Trevor Allen, David Robinson, Phil Cummins, Trevor Dhu and John Schneider

Geoscience Australia, the Australian National Committee on Large Dams (ANCOLD), and Environmental Systems & Services (ES&S) are collaborating on a project to develop earthquake ground-motion models to improve earthquake hazard and risk assessments in Australia. Here we discuss the importance of such models, which have the potential to substantially reduce uncertainties in estimates of earthquake hazard and risk. This problem is important for Australia, where the lack of ground-motion data and models means that the uncertainty in predicted ground-motion is the dominant factor that controls uncertainty in risk and hazard assessments.

Progress thus far consists in analysing a dataset comprising some 400 seismograph and accelerograph records for 67 events from the Burakin 2001-02 earthquake swarm. Events range in size from moment magnitude 2.2 ≤ M ≤ 4.5. These data were compiled to develop a regional ground-motion model for the Yilgarn Craton, southwestern Western Australia (WA). Modelled horizontal-component spectral displacement amplitudes fit the observed data well. Amplitude residuals (predicted – observed amplitudes) are, on average, relatively small and do not vary significantly with distance from the earthquake.

Since these data were recorded from an earthquake swarm, we have reason to suspect that the spectral shapes observed may not be characteristic of isolated crustal earthquakes, particularly at low magnitudes. Our ground-motion model may therefore have limited application for predicting ground-motions for other earthquakes, particularly at periods less than 0.5 s. This gives added impetus for the need to include more data in our work and to expand this research into different seismotectonic regions within the Australian continent. Nonetheless, this paper provides an important framework for developing ground-motion relations in Australia for use in engineering design.

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