Abstract
Activity on low deformation rate faults are challenging to quantify and comparatively understudied. One such fault, the Mangatangi Fault, strikes NE‐SW along the southeastern flanks of the Hunua Ranges c. 52 km south of New Zealand's most populous city, Auckland. It is part of a series of regional normal faults that reactivated since the Miocene; yet, its slip rate and earthquake recurrence interval is poorly constrained. In this study, we present geomorphic, geochronological, and geophysical data supporting vertical fault displacement rates of 0.017–0.27 mm yr−1 . Holocene rates (0.14–0.27 mm yr−1 ) compared to long–term rates (0.017–0.049 mm yr−1 ) highlight temporal variability in fault behaviour and earthquake clustering. The maximum earthquake magnitude is estimated as M W 6.8–6.9, with a recurrence interval ranging anywhere between 8100–127,100 years. Although ruptures along the Mangatangi Fault are interpreted to be infrequent over geologic timescales, dating of truncated sediments in the piedmont scarp constrain at least two Late Quaternary events, including one in the early Holocene. These results indicate that the Mangatangi Fault may pose greater seismic hazard to the Auckland area than previously considered, which, given high exposure and vulnerability, could translate into significant risk.