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Shallow Tectonic Stress Magnitudes at the Hikurangi Subduction Margin, New Zealand
  • Effat Behboudi,
  • David Daniel McNamara,
  • Ivan Lokmer
Effat Behboudi
School of Earth Sciences

Corresponding Author:[email protected]

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David Daniel McNamara
University of Liverpool
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Ivan Lokmer
University College Dublin
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Quantifying tectonic stress magnitudes is crucial in understanding crustal deformation processes, fault geomechanics, and variable plate interface slip behaviors in subduction zones. The Hikurangi Subduction Margin (HSM), New Zealand is characterized by along-strike variation in interface slip behavior, which may be linked to tectonic stress variations within the overriding plate. This study constrains in-situ stress magnitudes of the shallow (<3km) overriding plate of the HSM to better understand its tectonics and how they relate to larger scale subduction dynamics. Results reveal σ3: Sv ratios of 0.6-1 at depths above 650-700 m TVD and 0.92-1 below this depth interval along the HSM and SHmax: Sv ratios of 0.95-1.81 in the central HSM, and 0.95-3.12 in the southern HSM. These stress ratios suggest a prevalent thrust to strike-slip (σ1=SHmax) faulting regime across the central and southern HSM. In the central HSM, the presence of NNE-NE striking reverse faults co-existing with a modern σ1 aligned ENE-WSW (SHmax) suggests that overtime the stress state here evolved from a contractional to a strike-slip state, where the compressional direction changes from perpendicular (NW-SE) to subparallel (ENE-WSW) to the Hikurangi margin. This temporal change in stress state may be explained by forearc rotation, likely combined with development of upper plate overpressures. In the southern HSM, the modern WNW-ESE/ NW-SE σ1 (SHmax) and pre-existing NNE-NE striking reverse faults indicate that stress state remains contractional and subparallel (NW-SE) to the Hikurangi margin overtime. This may reflect the interseismic locked nature of the plate interface.