Exploring the Relationship Between Stress State and Fault Stability at the Hikurangi Subduction Margin, New Zealand

The Hikurangi Subduction Margin (HSM), New Zealand is characterized by along‐strike variation in slip behavior, linked to spatial‐temporal variations of plate interface coupling, tectonic stresses, and pore fluid pressures ( P p ) in the overriding plate. This study investigates fault dilation and slip tendencies within the HSM overriding plate under constrained stress states to better understand the geomechanical behavior of these structures and their role in varied slip behaviors of the HSM. Results reveal a transition from shear to hybrid failure in central HSM upper plate faults, and from compactive shear to shear failure in the south, suggesting increased vertical permeability in the central HSM. The decrease in vertical permeability from north to south coincides with variation in seismic behavior, from aseismically creeping and shallow Slow Slip Events (SSEs) in the north and central HSM, to an interseismically locked subduction interface in the south. Our findings suggest SSE distributions and characteristics along HSM are influenced by both along‐strike variations in upper‐plate vertical permeability and fluid conditions of the subducting slab. Transient P p fluctuations in the subducting plate may facilitate fluid migration to the subduction interface and overriding plate, increasing P p to trigger SSEs on the subduction interface. While SSE recurrence interval may depend on P p at the subduction interface and in the subducting plate, their duration, and the rate P p decreases may be controlled by the time required for dilational fault's permeability to increase in response to SSE‐induced stresses, allowing high P p to migrate from the subduction interface into the overriding plate.