Three‐Dimensional Surface Deformation in the 2016 M_W7.8 Kaikōura, New Zealand, Earthquake From Optical Image Correlation: Implications for Strain Localization and Long‐Term Evolution of the Pacific‐Australian Plate Boundary

Abstract

We generated dense, high‐resolution 3‐D ground displacement maps for the 2016 MW 7.8 Kaikōura, New Zealand earthquake—the most geometrically and kinematically complex rupture yet recorded—from 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 ~0.1 m, and vertical is ~0.5 m. Net slip measurements range from <1 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 Kaikōura 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 ~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 (~90%) of the surface deformation.

Three‐Dimensional Surface Displacements During the 2016 MW 7.8 Kaikōura Earthquake (New Zealand) From Photogrammetry‐Derived Point Clouds

“…The resolution of our vertical offset measurements is similar to our horizontal resolution (0.2–0.5 m in Figure c). The smallest vertical uncertainties calculated by Zinke et al () are ~0.2–0.3 m; however, many uncertainties on vertical offsets measured from OIC along the Kekerengu and Jordan faults are significantly larger (>1 m).…”

“…The field measurements in Figure c show several negative vertical offsets, where the SE side of the Kekerengu Fault was uplifted relative to the NW side. These SE side up measurements contrast with our offset measurements and those of Zinke et al (); the remote sensing measurements show consistent uplift of the NW side of the fault except at its NE end. In the region of the fault marked by “CT” in Figure c, corrupted data in our preearthquake point cloud prevent us from measuring displacements close to the fault.…”

“…For vertical offsets (Figure c), uncertainties on our measurements are significantly smaller than those of Zinke et al (), whose vertical displacement field is noisier than ours. Zinke et al () suggest that their poor vertical resolution is because satellite viewing angles were close to nadir (downward looking). The resolution of our vertical offset measurements is similar to our horizontal resolution (0.2–0.5 m in Figure c).…”

“…Dynamic rupture models have suggested that the 2016 rupture either (1) “jumped” 15–20 km from the Hundalee Fault to the Jordan Fault through dynamic‐stress triggering (Ando & Kaneko, ) or (2) propagated along an offshore fault to the Papatea Fault, before moving north to the Jordan‐Kekerengu system (Klinger et al, ; Ulrich et al, ). A third possibility is that rupture propagated more directly between the Hundalee and Jordan faults by rupturing the onshore Whites and Snowflake Spur faults (Zinke et al, ). Different studies have used different fault geometries; better constraints on fault geometry are required to test and compare these different dynamic rupture models. The coseismic behavior of the Papatea Block.…”

“…Comparison of our measured offsets with those from field surveys (Kearse et al, ) and optical image correlation (OIC; Zinke et al, ). (a) Map of field measurement sites and surface ruptures (red lines) along the Kekerengu fault.…”