The Nullarbor Plain is underlain by thick cratonic lithospheric mantle that is almost devoid of contemporary seismicity. Analysis of high‐resolution digital elevation models indicates neotectonic fault‐propagation fold traces on the nearly flat karst landscape that locally extend to lengths of >100 km, suggesting potential for hosting large (>7.3–7.5) moment magnitude earthquakes. Along‐strike maximum displacements are not proportional to neotectonic fold surface trace length but are spatially associated with crust‐scale electrical conductors identified in magnetotelluric surveys. Two major conductors penetrate from the upper crust to the uppermost mantle (at depths < 60 km) along crustal scale shear zones. Conductivity in the uppermost mantle shear zones is higher than conductivity at increased depth, suggesting fluid‐enhanced enrichment with hydrogen and/or carbon. Lithospheric fluid localization associated with ancient slab subduction and/or hydrothermal alteration may have weakened pre‐existing faults and enhanced neotectonic faulting in the Nullarbor Plain.

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/À14 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 À1 to >17 m Myr À1 (mean = 1.1 m Myr À1 ). Summation of displacements across faults yields crustal horizontal shortening rates lower than geodetically detectable resolution (≤0.01 mm yr À1 ) 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.

Using ground penetrating radar (GPR) we investigate the near surface (~0–10 m depth) geophysical structure of neotectonic fault-propagation folds and thrust faults in south-central Australia in varying stages of fold and fault growth. Variations in neotectonic fold scarp heights are interpreted to reflect variations in accumulated slip on the underlying reverse faults. Fold scarps on the Nullarbor and Roe Plains are characterized by broad, asymmetric morphologies with vertical displacements of ~5 to ~40 m distributed over 1 to 2 km widths (~0.5 to ~4 m per 100 m). Within increasing scarp height there is an increase in the frequency and spatial density of strong reflector packages in the hanging wall that are attributed to material contrasts imposed by co-seismic fracturing and associated lithological and weathering variations. No evidence for discrete faulting is found at scarp heights up to 40 m (maximum relief of 4 m per 100 m). Where the principal slip zone of a fault ruptures to the surface, scarp morphologies are characterized by steep gradients (ca. 10 m per 100 m). Discrete faulting is imaged in GPR as structural lineaments, abrupt changes in the thickness of reflector packages with variations of amplitude, and/or hyperbolic diffraction packages indicative of the disturbance of reflector packages. Geophysical imaging of subtle changes in the shallow geological structure during growth of fault-propagation folds can be conducted using GPR informing the identification of locations for invasive investigations (e.g., trenching).

The Nullarbor Plain is underlain by a thick cratonic lithospheric mantle, which is thought to have a paucity of neotectonic faults and seismicity. Based on the analysis of high-resolution digital elevation models, identified neotectonic fault traces on the nearly flat karst landscape locally extend >100 km long, suggesting potential for hosting large (>7.3 to 7.5) moment magnitude earthquakes. The measured along-strike maximum displacement Dmax for each trace is not proportional to surface rupture length (L) but is correlated with the occurrence of crust-scale electrical conductors identified in magnetotelluric surveys. Two major conductors penetrate from the upper crust to the topmost mantle along crustal scale shear zones. The conductivity value in the topmost mantle is much higher than in the cratonic mantle, indicating serpentinization of the mantle with the addition of fluids. Lithospheric fluid localization may have weakened pre-existing faults and enhanced neotectonic faulting in the Nullarbor plain.