Anisotropic structure under a back arc spreading region, the Taupo Volcanic Zone, New Zealand

摘要: [1] We investigate anisotropy surrounding a continental back arc spreading region, the Central Volcanic Region (CVR), in North Island of New Zealand and present simple method for spatial averaging to examine heterogeneous anisotropy. S phases from local earthquakes yield consistent trench-parallel fast directions (ϕ) southern, compressional region but varied northern, extensional region. In forearc east CVR, ϕ is nearly trench-parallel, suggesting shear mantle or flow. western 50 80 km depth give parallel extension (120°), 150 220 similar (150°). These results suggest asthenospheric flow with olivine axes oriented direction down 100–150 depth. eastern show mixed ϕ, that it transition between CVR forearc. Trench-parallel shallow events within may be caused by fluid-filled cracks. deeper SKS can explained standard fabrics developed lithospheric shearing, flow, fossil subducting oceanic lithosphere. Alternatively, they could part hydrous minerals at slab-mantle upper interface, which cause orient trench due maximum stress perpendicular along slab. We trench-perpendicular helps drive fluids away slab, while fails distribute fluids, explaining location changes geophysical properties.