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P wave azimuthal and radial anisotropy of the Hokkaido subduction zone
Author(s) -
Niu Xiongwei,
Zhao Dapeng,
Li Jiabiao,
Ruan Aiguo
Publication year - 2016
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2015jb012651
Subject(s) - geology , subduction , anisotropy , seismology , mantle wedge , slab , mantle (geology) , trench , seismic tomography , seismic anisotropy , geophysics , s wave , upwelling , azimuth , geometry , tectonics , oceanography , physics , quantum mechanics , chemistry , mathematics , organic chemistry , layer (electronics)
We present the first three‐dimensional P wave radial anisotropy tomography of the Hokkaido subduction zone, as well as P wave azimuthal anisotropy and S wave tomography, which are determined by inverting 298,430 P wave and 233,934 S wave arrival times from 14,245 local earthquakes recorded by 344 seismic stations. Our results reveal significant velocity heterogeneity, seismic anisotropy, and upwelling flows beneath the study region. In the mantle wedge, prominent low‐velocity (low‐V) anomalies exhibit trench‐normal fast‐velocity directions (FVDs) and a negative radial anisotropy (i.e., vertical velocity > horizontal velocity), which may reflect upwelling mantle flows. Fan‐shaped FVDs are found at depths of 65–90 km, and a detailed 3‐D mantle flow pattern is revealed, which may be caused by a combination of oblique subduction of the Pacific plate and collision of the Kuril arc with the Honshu arc beneath southern Hokkaido. The radial anisotropy changes at ~100 km depth, which may reflect variations in temperature and fluid conditions there. The subducting Pacific slab exhibits a positive radial anisotropy (i.e., horizontal velocity > vertical velocity), which may reflect the original fossil anisotropy when the Pacific plate formed at the mid‐ocean ridge.