Variable In Situ Stress Orientations Across the Northern Hikurangi Subduction Margin

We constrain orientations of the horizontal stress field from borehole image data in a transect across the Hikurangi Subduction Margin. This region experiences NW-SE convergence and is the site of recurrent slow slip events. The direction of the horizontal maximum stress is E-W at an active splay thrust fault near the subduction margin trench. This trend changes to NNW-SSE in a forearc trench slope basin on the offshore accretionary wedge, and to NE-SW in the onshore forearc. Multiple, tectonic, and geological processes, either individually or in concert, may explain this variability. The observed offshore to onshore stress rotation may reflect a change from dominantly compressional tectonics at the deformation front, to a strike-slip and/or extensional tectonic regime closer to the Taupo Volcanic Zone, further inland. In addition, the offshore stress may be affected by topography and/or stress rotation around subducting seamounts, and/or temporal stress changes during the slow slip cycle.