Systematic Estimation of Earthquake Source Parameters for Continental Australia: Attenuation and Stress Drop

ABSTRACT A new continental-scale Fourier spectral attenuation model is developed to resolve source parameters for well-recorded earthquakes occurring within Australian continental crust since 1994. The attenuation model uses almost 6200 individual earthquake recordings and is valid for hypocentral distances up to 2000 km. Assuming the Brune (1970)f−2 model, source parameters are derived for >290 earthquakes from moment magnitude 3.1≤M≤6.6. The stress-drop parameter (Δσ) is lognormally distributed with a median estimate of 1.85 MPa, ranging from <0.1 MPa to >60 MPa. The estimates of Δσ suggest significant regional variability in earthquake source characteristics for different seismotectonic regions, with earthquakes in Australia’s northwest and Flinders Ranges regions demonstrating stress drops consistently higher than the median value relative to other areas. Given Australia’s sparse monitoring network, it is difficult to attribute a physical justification (e.g., source depth) for this observation. Nevertheless, the regional variations in source parameters have utility for the selection and development of ground-motion models for national-scale and site-specific seismic hazard assessments in Australia. Importantly, the earthquake source parameters presented herein are explicitly anchored to the attenuation model developed in this study.