Three-Dimensional Surface Deformation in the 2016 MW 7.8 Kaikura, New Zealand, Earthquake From Optical Image Correlation: Implications for Strain Localization and Long-Term Evolution of the Pacific-Australian Plate Boundary

We generated dense, high-resolution 3-D ground displacement maps for the 2016 M-W 7.8 Kaikura, New Zealand earthquake-the most geometrically and kinematically complex rupture yet recordedfrom stereo WorldView optical satellite imagery using a new methodology that combines subpixel image correlation with a ray-tracing approach. Our analysis reveals fundamental new details of near-field displacement patterns, which cannot easily be obtained through other methods. From our detailed correlation maps, we measured fault slip in 3-D along 19 faults at 500-m spacing. Minimum resolvable horizontal slip is similar to 0.1 m, and vertical is similar to 0.5 m. Net slip measurements range from <1 to similar to 12 m. System-level kinematic analysis shows that slip on faults north of the Hope fault was oriented primarily subparallel to the Pacific-Australian plate motion direction. In contrast, slip on faults to the south was primarily at high angle to the plate motion and secondarily parallel to plate motion. Fault kinematics are in some locations consistent with long-term uplift patterns, but inconsistent in others. Deformation within the Seaward Kaikura Range may indicate an attempt by the plate boundary fault system to geometrically simplify. Comparison of published field measurements along the Kekerengu fault with our correlation-derived measurements reveals that similar to 36% of surface displacement was accommodated as distributed off-fault deformation when considering only field measurements of discrete slip. Comparatively, field measurements that project previously linear features (e.g., fence lines) into the fault over apertures >5-100 m capture nearly all (similar to 90%) of the surface deformation.