Style and episodicity of late Quaternary activity on the Pisa-Grandview Fault Zone, Central Otago, New Zealand

Abstract

The Pisa-Grandview Fault Zone in the upper Clutha valley of Central Otago, New Zealand, comprises major reverse faults in a Y-shaped pattern. Late Quaternary deformation associated with the zone follows the Pisa-Grandview (NW) branch and lies basinward of the master fault The deformation includes asymmetric folds and warps and associated antithetic reverse faults. Synthetic reverse faults are inferred to underlie the folds and warps. The relationships between the deformation and late Quaternary glacial and interglacial deposits suggest that activity along the Pisa-Grandview Fault Zone has occurred in episodic pulses. The duration of pulses of activity and quiescence is in the order of 10⁴ years. In addition, activity appears to Switch between the Pisa-Grandview and the Pisa-Lindis Peak branches at the northern end of the fault zone. These characteristics of fault activity lead to the hypothesis that the faults of Central Otago are interconnected as an imbricate system above a low-angle decollement thrust fault zone at mid-crustal depths. Earthquake and faulting activity may occur in episodic pulses across the region in response to a relatively uniform regional stress field.