Quaternary faults of south-central Australia: Palaeoseismicity, slip rates and origin

Abstract

Faults bounding the Flinders Ranges of South Australia and the Barrier Ranges of New South Wales display clear evidence of significant Quaternary displacements. Kinematic analysis of the Wilkatana, Burra and Mundi Mundi Faults indicates that reverse-oblique fault slip occurred in response to east – west compression, consistent with maximum compressive stress (SH_Max) orientations derived from historical earthquake focal mechanisms. Surface-rupturing events resulted from a series of moment magnitude (M) ≥6.6 palaeo-earthquakes over the past ∼100 000 years. The timing of the most recent surface-rupturing events was determined on each fault from optically stimulated luminescence dating of faulted and post-faulting strata. The Wilkatana Fault has been the site of at least two major earthquakes since around 67 ka, making this one of the youngest prehistoric fault scarp exposures in Australia. Thickness estimates of faulted Pliocene and Quaternary footwall sediment imply minimum fault slip rates of 20 – 30 m per million years, while extrapolation of a domed planation envelope in the bedrock hangingwall to the fault plane yields fault slip rates of 36 – 51 m per million years. Movement at these rates over the Pliocene to Holocene interval accounts for a significant proportion of the contemporary relief in the Flinders Ranges. The relative intensity of neotectonic activity and historical seismicity in the Flinders Ranges reflects the role of structural and thermal heterogeneities in a regional stress field dominated by far-field plate-boundary forces.

Key words:

• earthquakes
• faulting
• intraplate
• neotectonics
• Quaternary faults
• seismicity
• southern Australia
• stress

Acknowledgements

Dan Clark, Steven Hill and Chris Wilson are thanked for critical reviews of draft manuscripts that greatly improved this paper. We thank Wolfgang Preiss for drawing our attention to the Burra locality and Geoscience Australia for contributing financial support. Andrew Smart is thanked for access to the Wilkatana property.