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arXiv · 2610.33399

Ground-motion simulation of multi-segment ruptures on the Alpine-Marlborough fault system

Brendon A. Bradley·Jake Faulkner·Felipe Kuncar·Cesar A. Pajaro
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Abstract

The Alpine Fault (AF) is the major plate boundary crustal structure in New Zealand (NZ), producing large-to-great (M7-8+) earthquakes approximately every 300-500 years, and has long been a focal point for earthquake resilience in NZ. This study advances prior AF ground-motion modelling by considering multi-segment ruptures that initiate on the AF and rupture northward onto structures in the Marlborough Fault Zone (MFZ), resulting in ground shaking of consequential amplitudes for the upper South Island and Lower North Island, including Wellington city. From the 2022 NZ National Seismic Hazard Model (NSHM), three multi-segment rupture geometries including the Wairau, Clarence, and Hope fault structures in the MFZ are obtained, together with their scenario rupture rates. Hybrid broadband simulations using a multi-segment kinematic source description and a 3D NZ crustal velocity model are performed. Three rupture realizations per geometry are considered to compare the effects of kinematic rupture randomness with those of the different geometries. To provide comparisons with the prior ground-motion simulations used for public outreach in the AF8 programme, we also simulated the segmented M7.9 Alpine Fiordland-to-Kelly rupture geometry of Bradley et al. (2017a), adopting the same southern hypocentre location in all rupture scenarios, enabling examination of differences due to eight years of advancements in kinematic rupture and crustal velocity modelling. Results illustrate strong northward directivity and basin response, with the largest Wellington amplitudes resulting from the Alpine-Wairau and Alpine-Clarence scenarios -- peak ground accelerations of approximately 0.1 g, comparable to those observed during the 2016 Kaikōura earthquake; in aggregate, these Alpine-MFZ ruptures have a likelihood similar to the conventionally-considered Wellington Fault and Hikurangi subduction sources.

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Brendon A. Bradley, Jake Faulkner, Felipe Kuncar, Cesar A. Pajaro. 2026-10-24. Ground-motion simulation of multi-segment ruptures on the Alpine-Marlborough fault system. https://arxiv.org/abs/2610.33399

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