资源环境科技发展态势分析平台

Large earthquakes usually rupture plate boundary faults, releasing the accumulated stress as displacements localized along smooth, narrow faults. However, certain earthquakes initiate off main faults, rupturing adjacent, secondary faults. The mechanisms of such atypical stress release remain enigmatic, partly due to a lack of detailed geodetic evidence. Here, using the 3D coseismic displacement field derived from space imaging geodesy, we detect ten‐kilometer‐scale, nearly‐circular coseismic block rotation during the 2016 M_w 7.8 Kaikōura earthquake in New Zealand. Together, geodetic observations, longer‐term local paleo‐magnetic data, analytical and discrete element modeling imply that localized block rotation occurred south of the Hope fault along weak, steep, bedding‐parallel boundaries within a narrow, ~20‐kilometer‐wide dextral shear zone. That stress along plate boundary faults can be partially released in zones of distributed ruptures absorbing coseismic rotation may retard rupture along main faults. Our observations also suggest that coseismic rotation may help adjust plate boundary propagation.