Fluid-enhanced neotectonic faulting in the cratonic lithosphere of the Nullarbor Plain, Australia

Abstract

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.