Paleoseismology of the Hyde Fault, Otago, New Zealand

ABSTRACT We present the first paleoseismic investigation of the Hyde Fault, one of a series of north-east striking reverse faults within the Otago range and basin province in southern New Zealand. Surface traces of the fault and associated geomorphology were mapped using a lidar digital elevation model and field investigations. Trenches were excavated at two sites across fault scarps on alluvial fan surfaces. The trenches revealed stratigraphic evidence for four surface-rupturing earthquakes. Optically stimulated luminescence dating constrains the timing of these events to around 47.2 ka (37.5–56.7 ka at 95% confidence), 34.6 ka (24.7–46.4 ka), 23.5 ka (19.7–27.3 ka) and 10.5 ka (7.9–13.1 ka). We obtain a mean inter-event time of 12.4 kyr (2.3–23.9 kyr at 95% confidence) and the slip rate is estimated to be 0.22 mm/yr (0.15–0.3 mm/yr). We do not find evidence to suggest that earthquake recurrence on the Hyde Fault is episodic, in contrast to other well-studied faults within Otago, suggesting diverse recurrence styles may co-exist in the same fault system. This poses challenges for characterising the seismic hazard potential of faults in the region, particularly when paleoearthquake records are limited to the most recent few events.