Fault geometry and slip rates from the Nullarbor and Roe Plains of south-central Australia: Insights into the spatial and temporal characteristics of intraplate seismicity

Abstract

Analysis of TanDEM-X and Shuttle Radar Topography Mission (SRTM) data reveals geomorphic evidence for 292 fault-propagation fold scarps across the Miocene Nullarbor and Pliocene Roe Plains in south-central Australia. Vertical displacements (VD) are determined using topographic profiling of a subset (n = 48) of the fold traces. Fault dips (mean = 44 +16/−14° at 1σ) are estimated from seismic reflection data; the mean dip is assigned to faults with unknown dip and combined with VD to estimate net displacements (ND) and average net displacements (AD) for each fault. AD exceeds single-event displacements estimated from fault-length scaling regressions, indicating the identified faults have hosted multiple earthquakes. Combining AD with (i) faulted surface ages (Nullarbor ~10–5 Ma, Roe ~2.5 Ma), (ii) ages of faulted erosional–depositional features (e.g. relic Late Miocene dune fields and Pliocene paleochannels), and (iii) onset of the neotectonic regime in Australia at ~10 Ma yields average slip rates from <0.1 m Myr−1 to >17 m Myr−1 (mean = 1.1 m Myr−1). Summation of displacements across faults yields crustal horizontal shortening rates lower than geodetically detectable resolution (≤0.01 mm yr−1) since the Late Miocene. The ca. 10 Myr-long record of neotectonic faulting on the Nullarbor Plain provides important insights into earthquake spatial–temporal behaviours in a slowly deforming intraplate continental region.