Seismic Constraint on Heterogeneous Deformation and Stress State in the Forearc of the Hikurangi Subduction Zone, New Zealand

The Hikurangi subduction zone (HSZ) is the collisional boundary between the Pacific and Australian tectonic plates along the eastern coast of the North Island of New Zealand. The region is believed to be capable of hosting large megathrust earthquakes and associated tsunamis. Recent studies observe a range of slip behavior along the plate interface, with a sharp contrast between locked and creeping parts of the megathrust along the margin. This work uses teleseismic scattering data (receiver functions [RFs]) recorded at 53 long-running seismograph stations on the North Island of New Zealand to constrain the structure and mechanical properties of the forearc in the HSZ. We observe directional variations in RF phases at P–S converted delay times (i.e., depths) associated with the overlying forearc crust and note a general correlation with spatial variations in plate coupling as well as other geophysical properties. Our results suggest differences in the nature of crustal deformation (and stress state) along the Hikurangi margin, with evidence of clockwise rotation and/or extension in the northern HSZ, where the overriding forearc crust is uncoupled from the subducting Pacific slab.