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Journal: |
Journal of Geophysical Research 2019 No.8
clicks:275 |
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Title:
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Author:
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Yifan Gao |
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Adress: |
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Abstract:
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The eastern and northeastern Tibetan plateau is a key region to study
the growth and expansion of the plateau and associated extrusion
tectonics. We studied the seismic anisotropic structure in this region
by shear‐wave splitting analysis of teleseismic records from a dense
linear seismic array, to constrain the lithospheric deformation and
processes. We detected small‐scale variations in anisotropy, including
changes of splitting parameters around major faults and different
anisotropy patterns among individual tectonic blocks and units but with
consistent interior features. Our results combined with previous
observations suggest that, in addition to the dominant effects of
lateral extrusion induced by the India‐Eurasia collision, major faults
and tectonic heterogeneity may have also exerted significant impacts on
the deformation and thus anisotropic structure of the lithosphere. In
particular, we constructed two‐layer anisotropy models for both the
Longmenshan sub‐block in the easternmost Songpan‐Ganzi terrane and the
Western Qinling orogen, indicating crust‐mantle decoupling in these
areas. The lower anisotropic layer of both areas shows a general NW‐SE
fast polarization direction (FPD). We attribute this feature to the
large‐scale mantle deformation, due to the lateral extrusion of Tibet
associated with the India‐Eurasia collision. The upper‐layer anisotropy
in both areas features an optimal NEE‐SWW FPD. While in the Longmenshan
sub‐block it may stem from crustal deformation under the combined
effects of mid‐lower crustal flow, faulting and tectonic heterogeneity,
that in the Western Qinling Orogen is probably resulted from shearing
caused by upper‐crustal displacement along a mid‐crustal detachment. |
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