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We use new paleoseismic data and lidar to reassess late Quaternary activity of the NW (northwest) Cardrona Fault, a ∼60 km long range-bounding fault in Otago. Paleoseismic investigations of the NW Cardrona Fault were conducted in the 1980s, but findings were limited by a paucity of materials suitable for dating. Here, re-exposure and re-assessment of a 1980s trench at Macdonalds Creek provide stratigraphic evidence for two surface rupturing earthquakes on the NW Cardrona Fault. Through Optically Stimulated Luminescence dating and OxCal modelling, we estimate these earthquakes occurred at (mean ± 2 standard deviations, σ) 20.5 ± 7.8 ka and 8.7 ± 6.6 ka. The timings of these earthquakes are consistent with those proposed from re-interpretation of another 1980s trench on the NW Cardrona Fault in the Kawarau River valley, ∼25 km farther south. The slip rate and recurrence interval derived from the Macdonalds Creek trench data are 0.13 ± 0.05 mm/yr and 11,800 ± 5100 years (2σ error) respectively. These estimates imply lower slip rates and longer earthquake recurrence intervals on the NW Cardrona Fault than previously assessed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]