Spatio-temporal variability of slip rates and rupture extents from geomorphic features along the northern Alpine Fault, Aotearoa New Zealand

James La Greca, Robert M. Langridge, & Mark C. Quigley

Submitted September 7, 2025, SCEC Contribution #14661, 2025 SCEC Annual Meeting Poster #TBD

The northern Alpine Fault exhibits structural complexities that could influence the rupture extents and magnitudes of future earthquakes. Slip rates decrease from towards the northeast, ranging from 6 mm/yr to 14 mm/yr, with rates typically derived from late Holocene (1 – 2 ka) alluvial terrace offsets. Here, we present Mid to Early Holocene slip rates along northern Alpine Fault and consider their implications for rupture segmentation and temporal variability. We combine detailed geomorphic mapping from lidar data and use OSL dating to establish ages of associated geomorphic features and derive geological slip rates. Three areas are examined, the boundary between the northern and central Alpine Fault, sites proximal to Springs Junction, and the Glenroy Valley. These sites exhibit 10s to 100s of meters of right lateral and/or vertical offset. At the boundary of the northern and central Alpine Fault, slip rates are as high as 20 ± 2 mm/yr. Near Springs Junction, recalculating the rate anchored to the most recent earthquake, provides a ~13 mm/yr slip rate. Trench logs show evidence for only three Holocene earthquakes through the Glenroy Valley of the Alpine–Wairau Bend. We identify the Alpine-Wairau Bend as a potential rupture terminator including the possibility for terminations of ruptures at junctions of the Alpine Fault with the Marlborough Faults. This has implications for hazard characterization in how the Alpine Fault is considered in fault source models, the potential rupture extent, and whether slip along the principal rupture is constant or segmented along-strike during the next Alpine Fault rupture.

Key Words
Alpine Fault, Slip Rates, Rupture Segmentation, Paleoseismology

Citation
La Greca, J., Langridge, R. M., & Quigley, M. C. (2025, 09). Spatio-temporal variability of slip rates and rupture extents from geomorphic features along the northern Alpine Fault, Aotearoa New Zealand. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology