QUATERNARY TECTONIC DEFORMATION IN THE STABLE CONTINENTAL REGION OF CENTRAL WESTERN AUSTRALIA

Central Western Australia is a stable continental region (SCR) that has experienced repeated large magnitude earthquakes that have diverted streams, impounded lakes, and episodically reversed the flow of rivers. The Mt. Narryer fault zone is a ~120 km long left-stepping en echelon reverse-dextral fault system that includes, from south to north, the Sandford River, Roderick River, and Mt. Narryer fault segments. The principal scarps have been mapped previously using remote sensing, but have not been paleoseismically investigated. The fault system likely is responsible for Australia’s largest recorded onshore earthquake, the 1941 M_w 7.1 to 7.3 Meeberrie event, and the tectonic geomorphology indicates that individual faults within the system have experienced multiple previous Quaternary events.

Lake Wooleen is a fault dammed lake at the confluence of the Roderick and Murchison Rivers. The ~60 km long Roderick River scarp dams Lake Wooleen and reaches 8 meters in height along the west side of the lake. The Roderick River terminates at the Lake Wooleen scarp; during years of high flow Lake Wooleen overflows into the Murchison River then flows downstream to the west through a channel incised through the scarp. There is geomorphic evidence and historic documentation of the Murchison River episodically flowing upstream into Lake Wooleen causing the lake to back up into the Roderick River. The lake is ephemeral and most years during historic times remains dry.

The adjacent landscape is predominantly characterized by low relief sheetwash pediments that are overlain with ripple trains formed during infrequent high-intensity precipitation events. The region’s arid climate, low gradient rivers, and low relief landscape is highly sensitive to minor perturbations in both climate and tectonically driven land-level changes. The robust geomorphic record preserved along the fault traces is unique for Western Australia and includes fault scarps, fault dammed lakes, fault captured streams, sag ponds, fluvial terraces, and paleoshorelines. These features provide a good opportunity to address ongoing questions about fault behavior in SCRs and will help establish control on rupture segmentation, style of deformation, and an event chronology for the system.