The magnitude and principal direction of seismic azimuthal anisotropy provide key constraints on the deformation processes occurring within the Earth. Although this technique has been successfully applied to a variety of geological settings, high-resolution, three-dimensional anisotropic P-wave velocity model of the shallow part of a subduction zone was never yet achieved.
Arai et al.  provide the first of such models for the Northern Hikurangi subduction zone, where slow earthquakes are known to occur periodically. Deriving this high-resolution model was made possible through an exceptional dataset that resulted from one of the densest and most targeted 3D ocean bottom deployments in a subduction zone. The model highlights larger azimuthal anisotropy close to active faults and to the deformation front. Using the magnitude of the anisotropy, the authors attribute this clear fault related anisotropy to the preferentially oriented cracks and/or clay rich layers along these faults.
These results improve our understanding of the relationship between properties of the shallow part of the subduction zones and slip behavior on the plate boundaries.
Citation: Arai, R., Kodaira, S., Henrys, S., Bangs, N., Obana, K., Fujie, G., et al. . Three‐dimensional P wave velocity structure of the northern Hikurangi margin from the NZ3D experiment: Evidence for fault‐bound anisotropy. Journal of Geophysical Research: Solid Earth, 125, e2020JB020433. https://doi.org/10.1029/2020JB020433
―Anne Bécel, Associate Editor, JGR: Solid Earth