Newly discovered active faults in the Wairarapa Valley: Implications for multi-fault rupture and kinematics in the southern North Island, Aotearoa New Zealand

Genevieve Coffey , Nicola Litchfield, Regine Morgenstern, Rob Langridge, Dougal Townsend

Active fault locations and constraints on the timing and size of earthquakes are important for understanding and mitigating seismic hazard in Aotearoa New Zealand. However, historical and instrumental records are too short to provide these data on most earthquake-generating faults. Light detection and ranging (lidar) data provide us with the ability to locate and describe active faults and importantly, help us fill gaps in the paleoseismic record. A recent update to active fault mapping in the Wairarapa Valley has led to the discovery of seven new faults along with many new traces along previously identified faults. Four of these newly identified faults, (the Ruamahanga, Woodside, Carters Line, and Pāpāwai faults) are close to population centres and have slip rates and recurrence intervals of 0.1 - 1.1 mm/yr, and 770 - <15,000 years respectively. This work has revealed that active faults are distributed more widely across the Wairarapa Valley than previously thought, particularly in areas of geometric complexity. Fault-scarp gradients and paleoseismic constraints developed here suggest that faults in the Wairarapa Valley tend to rupture as part of multi-fault earthquakes with surface rupture during the 1855 CE earthquake on the Wairarapa Fault being more widespread than previously thought.