Large earthquake recurrence on the southern Willunga Fault, South Australia

The presence of Pliocene marine sediments in the Myponga and Meadows basins within the Mt Lofty Ranges south of Adelaide is testament to over 200 m of tectonic uplift within the last 5 Myr (e.g., Sandiford 2003, Clark 2014). The spatiotemporal distribution of uplift amongst the various faults within the range and along the range fronts is poorly understood. Consequently, large uncertainties are associated with estimates of the hazard that the faults pose to proximal communities and infrastructure.   We present the preliminary results of a paleoseismic investigation of the southern Willunga Fault, ~40 km south of Adelaide. Trenches were excavated across the fault to examine the relationships between fault planes and sedimentary strata. Evidence is preserved for 3-5 ground-rupturing earthquakes since the Middle to Late Pleistocene, with single event displacements of 0.5 – 1.7 m. Dating of samples will provide age constraints on the timing of these earthquakes. This most recent part of the uplift history may then be related to the longer-term landscape evolution evidenced by the uplifted basins, providing an enhanced understanding of the present-day seismic hazard. This abstract was presented at the Australian & NZ Geomorphology Group (ANZGG) Conference in Alice Springs 26-30 September 2022. https://www.anzgg.org/images/ANZGG_2022_First_circular_Final_V3.pdf