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.