[SCG58-17] Seismic evidence for fault-bound anisotropy and its implications on fault structure in the northern Hikurangi subduction zone
Keywords:Subduction zone, Seismic anisotropy, Fault structure
Seismic anisotropy around the shallow plate interface is often interpreted to be caused by preferentially-oriented cracks in a compressional stress regime associated with plate subduction. Our findings suggest that the anisotropic features are not ubiquitous and homogeneous within the overriding plate but more localized along the active thrust faults. We also found that the magnitude of anisotropy is roughly equivalent to the values reported in the spreading centers where the ridge-perpendicular extensional stress regime is dominant and thus aligned fractures, or cracks, are primary controls on crustal anisotropy (e.g. Dunn, 2015). In the case of subduction zones, the porosity along the faults is not expected to increase significantly due to the compressional stress regime as implied by the core samples from the splay fault in our study area (Fagereng et al., 2019). These considerations may indicate that both the orientation of cracks and the foliation structure, related to fault slip, contribute to seismic anisotropy.