Re‐evaluation of late Quaternary displacement along the Old Man Fault Zone at Gorge Creek, Central Otago, New Zealand

Abstract

Abstract Late Quaternary vertical displacement along the Old Man Fault Zone between Roxburgh and Alexandra, Central Otago, has been inferred previously from the observation of a newly formed scarp and a stream‐bank exposure showing crushed schist overlying late Quaternary alluvium at Gorge Creek. Both localities are in regions of active surficial slope failure. The lack of definitive criteria to distinguish between tectonic faulting and slope processes suggests that the most likely cause for the emplacement of broken schist over late Quaternary gravel and sand at Gorge Creek is from the failure and downslope movement of schist. Scarps formed by horizontal motion without accompanying seismicity are also likely to be the result of local land instability. A flight of unfaulted Clutha River terraces 15 km to the south of Gorge Creek confirms that there has been no surface fault displacement along the Old Man Fault Zone in the last c. 350 000–250 000 years.