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

Authors / CoAuthors

Clark, D. | Cupper, M. | Sandiford, M. | Kiernan, K.

Abstract

Geomorphic mapping of the ~30 km Lake Edgar fault scarp in SW Tasmania suggests that three large surface-rupturing events with vertical displacements of 2.4 - 3.1 m have occurred in late Quaternary times. Optically stimulated luminescence (OSL) chronology from a sequence of three periglacial fluvial terraces associated with scarp incision provides constraint on the age of these events. The ages of alluvial/colluvial fans derived from the youngest fluvial terraces constrain the most recent event to ca 17 - 18 ka. The chronology of the two preceding events is more poorly constrained. The near coincidence of ages from the base of the youngest terrace and the penultimate terrace suggest that penultimate faulting might have occurred during active fluvial deposition ca 25 - 28 ka. The oldest recognised event occurred subsequent to the ca 61 ka deposition of gravels on the highest of the three terraces and prior to the deposition of ca 48 ka gravels exposed in the footwall fan. The vertical displacement implies earthquake magnitudes in the order of MW 6.8 - 7.0. Estimates for the average slip rate calculated for the two complete seismic cycles range from 0.17 - 0.20 mm/yr (unweighted mean). This sequence represents the first recurrence data for surface-rupturing earthquakes on an eastern Australian Quaternary fault. The Lake Edgar Fault, which originally formed in the Palaeozoic, is undoubtedly susceptible to reactivation under conditions imposed by the contemporary Australian intraplate stress field. While displaying episodic rupture behaviour, the fault appears to rupture with a "characteristic" magnitude. These findings are significant for seismic hazard assessment both in Australia and in intracratonic areas worldwide.

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nonGeographicDataset

eCat Id

61364

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Keywords

• External Publication

( Theme )

• climate

( Theme )

• earthquakes

( Theme )

• geohazards

• AU-TAS

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

Publication Date

2004-06-22T00:00:00

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geoscientificInformation

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[-43.20, -42.80, 146.25, 146.50]

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