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Fault Zone Structure of the Alpine Fault in New Zealand Imaged by Seismic Receiver Functions

The Alpine Fault in New Zealand is a major continental transform fault that is late in its earthquake cycle, offering a rare opportunity to study strike-slip systems before the next large earthquake. Paleoseismological studies indicate that ruptures of past great earthquakes commonly either terminate within or propagate through boundary zones between major fault sections of the Alpine Fault, where the fault geometry varies. Direct constraints are required for further refinement of the fault geometries at crustal depths. Here, we deployed a dense nodal array of 23 stations with ~100 m spacing for a few months in 2023 cross a 1.5-km-long profile spanning the Alpine Fault trace at Haast, South Island, New Zealand. This array sits atop a critical boundary zone characterized by an abrupt near-surface dip change and by documented terminations of large earthquake ruptures. Teleseismic P receiver functions (RFs) computed from these nodal seismometer data present dramatic, characteristic polarity reversals over backazimuth observed on both radial and transverse components, indicative of complex fault-parallel, dipping fault zone structures at crustal depths. In particular, we observe (1) distinct negative-amplitude arrivals at zero delay time clustered in 180 azimuths on radial RFs for individual stations; and (2) an across-fault change of the polarity-reversal patterns in RFs for stations located opposite sides of the fault, with a clear dependence on incoming waves direction. We perform 2-D finite-difference simulations to model these characteristic RFs, which suggests a single dipping fault cannot reproduce our observations. Instead, the new observations require at least two fault planes with finite widths and moderate dipping angles, indicating a structurally complex fault zone at depths. We infer that the fault zone structural complexity at boundary between the central and south segments of the Alpine Fault play a role in governing earthquake rupture arrest or propagation, with direct implications for hazard assessment.

Session: Physical Properties of Fault Zones from the Seismic Source to Earth’s Surface [Poster]

Type: Poster

Room: Exhibit Hall A+B

Date: 4/15/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Meghan Miller

Student Presenter: No

Invited Presentation: 

Poster Number: 127

Additional Authors