2018 – Evaluating potentially active tectonic faults for probabilistic seismic hazard assessments in Australia

Dee Ninis, Elodie Borleis & Wayne Peck

For intraplate regions such as Australia, identifying and quantifying activity on tectonic faults for inclusion in probabilistic seismic hazard assessments can be challenging due to the typically long return period for ground-rupturing earthquakes associated with these structures. Return periods of 10,000’s to 1,000,000’s of years mean that surface displacement evidence is prone to degradation through erosion and burial, and paleoseismological ‘trench’ excavations may not uncover geology old enough to reveal previous events. As a consequence, there is often little or no preserved evidence of past ground rupturing events on these structures. Rather than ignoring faults which show no evidence of neotectonic displacement, we present an alternative approach; in addition to considering active faults (movement in the last 35,000 years) and neotectonic faults (movement in the last 10 Myr) in seismic hazard assessments, we also consider faults which otherwise show no evidence of neotectonic activity but which are aligned favourably with the current stress regime and are therefore potential sources of earthquakes and accompanying strong ground motion.