How Subduction Margin Processes and Properties Influence the Hikurangi Subduction Zone

The Hikurangi margin has been an important global focus for subduction zone research for the last decade. International Ocean Discovery Program drilling and geophysical investigations have advanced our understanding of megathrust slip behavior. Along and across the margin, detailed imaging reveals that the megathrust structure varies spatially and evolves over time. Heterogeneous properties of the plate boundary zone and overriding plate are impacted by the evolving nature of regional tectonics and inherited overriding plate structure. Along-strike variability in thickness of subducting sediment and northward increasing influence of seamount subduction strongly influence megathrust lithologies, fluid pressure, and permeability structure. Together, these exert strong control on spatial variations in coupling, slow slip, and seismicity distribution. Thicker incoming sediment, combined with a compressional upper plate, influences deeper coupling at southern Hikurangi, where paleoseismic investigations reveal recurring great (M w > 8.0) earthquakes. ▪ The Hikurangi Subduction Zone is marked by large-scale changes in the subducting Pacific Plate and the overlying plate, with varied tectonic stress, crustal thickness, and sediment cover. ▪ The roughness of the lower plate influences the variability in megathrust slip behavior, particularly where seamounts enhance subduction of fluid-rich sediments. ▪ Variations in sediment composition impact the strength of the subduction interface, with the southern Hikurangi Subduction Zone exhibiting a more uniform megathrust fault. ▪ Properties of the upper plate influence fluid pressures and contribute to the observed along-strike variations in Hikurangi plate coupling and slip behavior.