Large earthquake recurrence in the Sprigg Orogen, South Australia and implications for earthquake hazard assessment

Dan Clark

The Australian continent is actively deforming at a range of scales in response to far-field stresses associated with plate margins, and buoyancy forces associated with mantle dynamics. On the smallest scale (several 10’s of km), fault-related deformation associated with far-field stress partitioning has modified surface topography at rates of up to approximately 100 m/Myr. This deformation is evidenced in the record of historical earthquakes, and in the pre-historic record in the landscape. Paleoseismological studies indicate that few places in Australia have experienced a maximum magnitude earthquake since European settlement, and that faults in most areas are capable of hosting potentially catastrophic earthquakes with magnitudes in excess of 7.0. South Australia is well represented in terms of its pre-historic earthquake record. Seismogenic faulting in the last 5-10 million years is thought to be responsible for generating more than 30-50% of the contemporary topographic relief separating the highlands of the Flinders and Mt Lofty Ranges from adjacent plains, and perhaps as much as a third of the strain budget of the entire continent is accommodated there. Adelaide itself straddles several faults which are arguably some of Australia’s most active. Decisions relating to the siting and construction of the built environment should therefore be informed with knowledge of the local neotectonics.