Identifying Active Faulting in the Flinders Ranges, South Australia, Using a Temporary Seismometer Deployment

Compared to the rest of continental Australia, the Flinders Ranges region of South Australia stands out not only because of its high topographic relief, but also because of its high seismicity and high fault density. The high density of thrust faults combined with their relatively high Quaternary slip rates indicate that the Flinders and Mt. Lofty Ranges comprise a region of pronounced neotectonic activity. Applying the accumulating body of neotectonic evidence to an assessment of earthquake hazard in South Australia requires determining what relationship exists, if any, between the earthquakes and faults. If it can be shown that the seismicity tends to cluster along faults, then neotectonic and paleoseismological studies focused on these active faults can help constrain the size and frequency of earthquakes. If there is no evidence of clustering, then an assessment of earthquake hazard will rely more heavily on the very short history of recorded earthquakes

We describe the use of a temporary seismometer deployment to monitor local earthquakes in the Flinders Ranges, South Australia. 16 seismograph stations were deployed over a 200 x 100 km area, which is one of the most seismically active regions in Australia. The instrumentation consisted of short-period and broadband Guralp seismometers combined with Reftek and Kelunji data loggers, which sample data continuously at 100-200 sps. Analysis of data from the period Sept.-Dec., 2003, resulted in the determination of hypocentres for over 175 earthquakes, most of which could not be located using PIRSA¡_s permanent network. 54 of these earthquakes had depths resolved at 10 km or greater, and the proportion of deep events appears to increase from the southern to the northern part of the Flinders Ranges. The largest earthquake, ML¡Ö4, occurred near Hawker on 22 November, 2003, and has a depth of 17¡A2 km, and a well-resolved normal focal mechanism. This result is surprising given that the regional stress field is widely assummed to be compressive, and we will discuss implications for lithospheric deformation in the Flinders Ranges.