Fluid-Enhanced Neotectonic Faulting in the Cratonic Lithosphere of the Nullarbor Plain in South-Central Australia

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.