Influence of Structural Maturity on the Rupture Morphology of the Northern Alpine Fault, Aotearoa New Zealand

Abstract The Alpine Fault (AF) in Aotearoa New Zealand is a fast‐slipping plate boundary fault late in its seismic cycle that presents a major source of seismic hazard. Past earthquakes have created a structural‐geomorphic record of surface ruptures that we map and analyze for the northern AF using 1,000 of Light Detection and Ranging data and field studies. Mapped surface structures ( n = 4,500) are classified as either Principal Fault Traces (PFTs), Distributed Alpine Fault Traces (DAFTs), Secondary Active Faults, or Secondary Structures (SSs). Derivation of quantitative metrics including PFT and DAFT zone widths, fault trace corrugation, and topographic sinuosity reveal along‐strike variations that correlate with accumulated geological displacements, AF slip rate variations, and spatial relationships to other major faults. Collectively, this suggests that structural characteristics of Holocene‐Pleistocene earthquakes on the northern AF vary with fault structural maturity and neighboring fault interactions. On this basis we classify the northern AF into 4 distinct segments with implications for future rupture extents and structural characteristics. Maximum PFT and DAFT zone widths range from 500 m to 1,700 m and 1,500 m to 4,000 m, respectively, along the segments of the northern AF. Our results highlight the potential for plate boundary faults to produce wide and structurally complex ruptures.