THE POTENTIAL FOR PALEOLIQUEFACTION STUDIES TO CONTRIBUTE TO AUSTRALIA'S EARTHQUAKE HAZARD MAP

Australia has a low rate of modern seismicity and a short historical record of earthquakes. Both of these factors combined make it difficult to lead to large uncertainties construct regarding an earthquake hazard map for Australia in which we can have complete confidence. The current hazard map is based exclusively on historical and instrumentally recorded seismicity. It is an open question whether this is a valid characterisation of seismicity over the long term. Recent neotectonic investigations in areas of low topographic relief, for example, indicate that seismicity must be transitory in both space and time over large parts of Australia.

One approach to address the problem of sparse seismicity in intraplate regions like Australia is to use paleoliquefaction studies to constrain the occurrence of prehistoric earthquakes. Liquefaction has been observed following large historic earthquakes in South Australia and Victoria , and numerous ‘sand blowsEwere observed following the 1968 Meckering earthquake (Ms 6.8) in Western Australia. It therefore seems likely that earlier, prehistoric earthquakes would have also induced liquefaction in these areas, as well as other areas which are geologically prone to liquefaction but have not experienced an historical earthquake.

We have identified 4 target areas for paleoliquefaction studies: (1) the Perth region, a major urban centre situated in a large sedimentary basin near the South West Seismic Zone; (2) the Murchison river area about 500 km north of Perth, which lies near the epicentres of two large historical earthquakes; (3) the southeastern tip of South Australia, site of pronounced liquefaction associated with a large (Ms 6.5) 1897 earthquake; and (4) the Goulburn river near the Cadell fault in Victoria, whose banks consist of poorly consolidated fluvial sediments and lies near a fault known to have experienced slip in the Quaternary. In this presentation, we will discuss why we have chosen these sites as having high potential for paleoliquefaction studies, and hope to present some results from preliminary surveys at of the four target areas.