Style and timing of late Quaternary faulting on the Lake Edgar fault, southwest Tasmania, Australia: Implications for hazard assessment in intracratonic areas

Abstract

Geomorphic analysis of the ~30-km-long Lake Edgar fault scarp in southwestern Tasmania suggests that three large surface-rupturing events with vertical displacements of 2.4 m to 3.1 m have occurred in late Quaternary time. Optically stimulated luminescence (OSL) age estimates from a sequence of three periglacial fluvial terraces associated with faulting constrain these events to ca. 18 ka, ca. 28 ka, and ca. 48–61 ka. A similar amount of vertical displacement during each faulting event suggests that surface-breaking earthquakes on this fault are characteristically of magnitude MW 6.8–7.0. Estimates for the average slip rate calculated over two complete seismic cycles range from 0.11 to 0.24 mm/yr, which is large for a stable continental region fault. This sequence represents the first recurrence data for surface-rupturing earthquakes on an eastern Australian Quaternary fault, and one of only a few for the entire Australian continent.