Distinct Crustal Structure Across the Alpine Fault, New Zealand: Seismic Imaging of a Through‐Going Vertical Fault Beneath Its Central Section

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Abstract
The Alpine Fault (Aotearoa New Zealand) is a major plate boundary transform fault, that quasi‐periodically hosts large (M7‐8) to great (M8+) earthquakes. The fault is thought to be segmented with sections rupturing both individually and in combination. Surface mapping indicates the fault changes from near‐vertically orientated in the South‐Westland Section, to dipping ∼45–60° SE in the Central Section, but it is unclear how this change is accommodated in the subsurface. We use receiver functions generated from long‐term seismic stations and a temporary array to image the subsurface at this section boundary. Using velocity inversion and common conversion point stacking, we find there are distinct crustal structures on either side of the fault trace. The subvertical fault likely extends northeastward past the section boundary and two fault structures may co‐exist beyond the section boundary. This geometry is consistent with microseismicity and previous tectonic studies, and helps to explain through‐going fault ruptures.
Funding Information
  • Natural Environment Research Council (NE/W008289/1)

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