Neotectonic defomation in the Western Australia shear zone

Paleoseismological, geomorphological, and geophysical studies of faults and fault-related folds reveal late Quaternary tectonic reactivation within western Australia’s former passive margin. Reactivation occurs along an approximately 2000 km long zone of dextral-oblique neotectonic faults and folds referred to as the Western Australian shear zone (WASZ). Offshore 2D and 3D seismic data reveal near sea bottom and seafloor expression of faults in the Carnarvon basin. High-precision leveling of modern and late Pleistocene shoreline features in the Cape Region indicates a systematic measurable change in relative paleo-sea level elevations consistent with late Neogene to Quaternary deformation on the Cape Cuvier and Cape Range anticlines. Analyses of ephemeral stream morphodynamics in the onshore Carnarvon basin demonstrate that tectonically driven land-level changes are affecting channel form and fluvial processes. Trenching investigations across neotectonic structures indicate four to six late Quaternary morphogenic earthquake events have occurred in the Mt. Narryer fault zone in the southern WASZ.
The WASZ reoccupies older rift related structures that initially formed during periods of continental-scale fragmentation in the Paleozoic and Mesozoic Eras. Reactivation is coincident with late Neogene and Quaternary reorganization of Australia’s northern plate boundary and realignment of the intraplate stress field. Neotectonic deformation in the southern WASZ is dominated by transpressional inversion within the extended crustal domain between Indian Oceanic crust to the west and non-extended Australian continental crust to the east. Folding in the near surface sediments is the predominant style of surface expression of reactivated basement faults. Tectonic deformation rates appear to decrease from north to south across the WASZ as indicated by historical seismicity and tectonic geomorphology. Rates of deformation in the region are low, however, active tectonic processes are occurring. The WASZ accommodates differential motion expressed as continental scale dextral oblique motion within a zone of extended crust between oceanic and non-extended continental tectonic blocks—or micro-plates.