Millennial forearc erosion driven by upper plate faulting, Southeastern North Island, Aotearoa New Zealand

The contributions of potential drivers of uplift and erosion in subduction zone forearcs over geologic time remain unknown. Proposed drivers include coseismic and interseismic earthquake cycle deformation associated with upper‐plate forearc faults and the underlying subduction interface. The Hikurangi subduction zone (HSZ), along the eastern North Island of Aotearoa New Zealand, provides a unique location to examine these controls, given both along‐strike variations in subduction zone coupling, as well a record of vertical motion from modern and prehistoric earthquakes on forearc faults and the plate interface. There, the Palliser–Kidnappers coastline (PKC) obliquely parallels the plate boundary in proximity to a number of forearc faults and spans a transitional boundary between currently locked and freely slipping portions of the subduction interface. Using digital topographic analysis and catchment‐averaged erosion rates from cosmogenic 10 Be, we examined the geomorphology of the HSZ forearc to evaluate connections between plate coupling and forearc erosion and uplift. In general, we find overall low concentrations of 10 Be and consequently high rates of erosion that mimic coastal uplift along the PKC, with high rates (>1 mm year −1 ) of erosion concentrated in the south near Cape Palliser. There, the southern Aorangi Range exposes deeper basement terrane rocks that are incised by the steepest fluvial drainages along the PKC, with positive correlation between normalised channel steepness ( k sn ), erosion rate and Late Pleistocene–Holocene uplift rates from marine terraces. Our findings indicate the highest forearc uplift rates occur above the narrow, locked portion of the HSZ, in an area near offshore oblique contractional deformation on the Palliser–Kaiwhata fault.