Surface Wave Dispersion from Recent Australian Earthquakes

Various imaging techniques have been deployed recently to make maps of the subsurface of Australia from seismic signal and ambient noise. These maps contribute to the understanding of structure and evolution of the Australian lithosphere, and can also improve understanding of the associated geohazards. Surface wave group velocity dispersion is one of the tools used to image the shallow subsurface, especially the crust and the uppermost mantle. Most surface wave velocity maps of Australia's subsurface were made using data from earthquakes that occurred at teleseismic distances, predominately along the subduction zones surrounding the continent to the west and east. Australia rarely has large magnitude earthquakes on the landmass, yet in the past year there have been two major earthquakes on the continent, a Mw=5.7 in South Australia and a Mw=5.4 in Victoria. The longer travel paths used in previous studies mean that the average velocity information inevitably included structures from offshore and away from the landmass. Data from earthquakes large enough to have excited surface waves that occurred on the continental crust in Australia are thus, arguably, a unique tool to scrutinize the current maps and provide additional information. This study incorporates data from 5 earthquakes and about 100 new paths within the Australian continent. The newly obtained Rayleigh wave group velocity dispersion curves are compared with dispersion curves and tomographic maps obtained using long source-receiver paths from the updated model of Yoshizawa and Kennett (2004) and with the PREM predictions (Dziewonski and Anderson, 1981). This allows for insight into how the offshore distance affects the results and presents the potential to create a better, higher resolution map of crustal and lithoshperic properties of Australia.