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Journal: |
Journal of Geophysical Research 2018 No.11
clicks:239 |
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Title:
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Author:
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Tuo Zheng1,2,3, Zhifeng Ding1, Jieyuan Ning2, Lijun Chang1, Xingchen Wang1 , Fansheng Kong3,4, Kelly H. Liu3 , and Stephen S. Gao3 |
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Adress: |
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Abstract:
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The fast orientation and magnitude of crustal azimuthal anisotropy beneath the southeastern
Tibetan Plateau and adjacent areas are measured by analyzing the sinusoidal moveout of the P to S
converted phase from the Moho. Beneath the tectonically active plateau, the mean magnitude is
0.48 ± 0.13 s, which is about twice as large as that observed in the stable Sichuan Basin (0.23 ± 0.10 s). The
two areas are separated by the Longmenshan fault zone, a zone of devastating earthquakes including the
12 May 2008 MW 7.9 Wenchuan earthquake. Fault orthogonal fast orientations observed in the southern
Longmenshan fault zone, where previous studies have revealed high crustal Vp∕Vs and suggested the
presence of mid-lower crustal flow, may reflect flow-induced lattice preferred orientation of anisotropic
minerals. Fault parallel anisotropy in the central segment of the fault zone is most likely related to fluid filled
fractures, and fault perpendicular extensional cracks are probably responsible for the observed anisotropy
in the northern segment. The crustal anisotropy measurements, when combined with results from previous
studies, suggest the existence of mid-lower crustal flow beneath the southeastern margin of the plateau.
Comparison of crustal anisotropy obtained before and after the Wenchuan earthquake suggests that the
earthquake has limited influence on whole crustal anisotropy, although temporal changes of anisotropy
associated with the earthquake have been reported using splitting of shear waves from local earthquakes
occurred in the upper crust. |
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