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Fault Geometric Complexity and Displacements of 2016 Kaikōura Earthquake Surface-ruptures, New Zealand

Description: 

The Kaikōura Earthquake ruptured a complex system of more than 20 faults in the northeastern South Island of New Zealand. These faults display a wide range of orientations, lengths, displacements, slip types and slip rates. We draw together information from the literature for fault-trace maps, displacement measurements, uplift and bedrock geology to examine controls on fault geometries and displacements in the Kaikōura Earthquake. The 2016 ruptures cross a tectonic domain boundary and their overall geometry is neither controlled by slip rate on individual faults nor by regional shear-strain rates. Instead, the complexity of 2016 faulting reflects the variable orientations of discontinuities in the underlying bedrock. The earthquake utilised a range of pre-existing zones of bedrock weakness including basement bedding/structures, Cretaceous normal faults, Miocene reverse faults and Cenozoic bedding planes. The resulting fault network is highly connected, with thrust faulting linking strike-slip faults at depths of 5-25 km and ‘jump’ distances < 1 km. High slip gradients approaching fault tips reflect slip transfer between faults and kinematic coherence across the fault system during the earthquake. Despite the geometric complexity of faulting, the sense of slip on each fault is broadly consistent with a ~120° regional principal horizontal shortening direction. However, many of the 2016 faults have orientations misfit for slip in the contemporary regional stress field, suggesting either local rotation of the principal stresses and/or dynamically triggered slip on misoriented faults. Complex multi-fault geometries are common for historical large-magnitude earthquakes in New Zealand and suggest that our observations have wide application.

Session: Exploring the Complexity of Fault Discontinuities - I

Type: Oral

Date: 4/17/2025

Presentation Time: 02:45 PM (local time)

Presenting Author: Andy

Student Presenter: No

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