Seismic anisotropy of the Northeastern Tibetan Plateau from shear wave splitting analysis

Li, Yonghua; Wu, Qingju; Zhang, Fengxue; Feng, Qiangqiang; Zhang, Ruiqing

doi:10.1016/j.epsl.2011.01.026

Cited by 74 publications

(73 citation statements)

References 53 publications

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“…The nearly W-E trend of high-Q direction θ in the northeastern TP is also close to the patterns of Global Position System velocity vector measurements [e.g. and shear wave splitting fast directions [e.g., Huang et al, 2000;Wang et al, 2008;Li et al, 2011]. This correlation supports the assumption of mechanical coupling between the crust and lithospheric mantle during their deformation in the northeastern TP.…”

Section: Lg and Pg Q Tomographysupporting

confidence: 72%

Collaborative Research: High-Resolution Seismic Velocity and Attenuation Models of Western China

Sandvol¹,

Ni²,

Hearn³

et al. 2014

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Section: Lg and Pg Q Tomographysupporting

confidence: 72%

Collaborative Research: High-Resolution Seismic Velocity and Attenuation Models of Western China

Sandvol¹,

Ni²,

Hearn³

et al. 2014

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“…Li et al 2011;Levin et al 2012;Wu et al 2015b). Computation of predicted SKS splitting with specific splitting analysis methods is beyond the scope of this paper, but we can infer, qualitatively, that the dominant E-W (central Tibet) and NW-SE (eastern Tibet) fastpropagation directions, as seen in the SKS-splitting observations (Fig.…”

Section: Origin Of Shear-wave Splitting Beneath Tibetmentioning

confidence: 99%

“…Two-layer modelling of shear-wave splitting has also been carried out at a number of other sites within the plateau (Levin et al 2008;Huang et al 2011;Li et al 2011;Levin et al 2012;Wu et al 2015b;Ye et al 2016). …”

Section: Origin Of Shear-wave Splitting Beneath Tibetmentioning

confidence: 99%

Complex, multilayered azimuthal anisotropy beneath Tibet: evidence for co-existing channel flow and pure-shear crustal thickening

Agius

Lebedev²

2017

Geophysical Journal International

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SUMMARYOf the two debated, end-member models for the late-Cenozoic thickening of Tibetan crust, one invokes "channel flow" (rapid viscous flow of the mid-lower crust, driven by topography-induced pressure gradients and transporting crustal rocks eastward) and the other-"pure shear" (faulting and folding in the upper crust, with viscous shortening in the mid-lower crust). Deep-crustal deformation implied by each model is different and would produce different anisotropic rock fabric. Observations of seismic anisotropy can thus offer a discriminant. We use broadband phase-velocity curves-each a robust average of tens to hundreds of measurements-to determine azimuthal anisotropy in the entire lithosphere-asthenosphere depth range and constrain its amplitude. Inversions of the differential dispersion from path pairs, region-average inversions and phase-velocity tomography yield mutually consistent results, defining two highly anisotropic layers with different fast-propagation directions within each: the middle crust and the asthenosphere.In the asthenosphere beneath central and eastern Tibet, anisotropy is 2-4 per cent and has a NNE-SSW fast-propagation azimuth, indicating flow probably driven by the NNEward, shallow-angle subduction of India. The distribution and complexity of published shear-wave splitting measurements can be accounted for by the different anisotropy in the mid-lower crust and asthenosphere. The estimated splitting times that would be ac-2 M.R. Agius and S. Lebedev cumulated in the crust alone are 0.25-0.8 s; in the upper mantle-0.5-1.2 s, depending on location. In the middle crust (20-45 km depth) beneath southern and central Tibet, azimuthal anisotropy is 3-5 and 4-6 per cent, respectively, and its E-W fast-propagation directions are parallel to the current extension at the surface. The rate of the extension is relatively low, however, whereas the large radial anisotropy observed in the middle crust requires strong alignment of mica crystals, implying large finite strain and consistent with high-rate horizontal flow. Together, radial and azimuthal anisotropy suggest eastward mid-crustal channel flow in central Tibet, along the regional topography gradient.In NE high Tibet, mid-crustal azimuthal anisotropy is 4-8 per cent and has WNW-ESE and NW-SE fast-propagation directions, parallel to the net extension at the surface. These fast directions are inconsistent with channel flow following the SW-NE regional topography gradient. Instead, they suggest similar net deformation in the (decoupled) shallow and deep crust. In the brittle upper crust, it is accommodated by strike-slip faulting; in the ductile mid-lower crust-by shear oriented at ∼45 • to the faults. Although mid-crustal flow beneath NE Tibet may transport some material towards the plateau periphery at a low region-average rate, the dominant mid-crust deformation pattern is shear parallel to the plateau boundary. This implies that channel flow from central Tibet is not the main cause of the on-going crustal thickening farther northeast.

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“…Receiver functions near the Qaidam basin showed a south-dipping velocity discontinuity in the upper mantle, which is interpreted as the top of the subducting Eurasia mantle lithosphere (Kind et al 2002), however, Yue et al (2012) observed a slightly northward dipping Moho underneath the Qaidam basin. Moreover, the shear wave splitting observation showed that a one-layer anisotropy model with a fast anisotropic direction trending NW-SE in the western and northern NET, is required to fit the model, but two anisotropic layers in the eastern NET (Li et al 2011). Furthermore, the connections between the LVZ in the crust and upper mantle and the Moho depth and their Ordos Q ia n g ta n g T e rr a n e Q a id a m B a s in S o n g p a n -G a n z i T e rr a n e Q il ia n O r o g e n Qin ling Oro gen implications for local tectonics remain open to debate due to limitations of different datasets and/or methods.…”

Section: Introductionmentioning

confidence: 99%

Crustal and upper mantle structure beneath the northeastern Tibetan Plateau from joint analysis of receiver functions and Rayleigh wave dispersions

Zheng

Shen

et al. 2015

Geophys. J. Int.

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Seismic anisotropy of the Northeastern Tibetan Plateau from shear wave splitting analysis

Cited by 74 publications

References 53 publications

Collaborative Research: High-Resolution Seismic Velocity and Attenuation Models of Western China

Collaborative Research: High-Resolution Seismic Velocity and Attenuation Models of Western China

Complex, multilayered azimuthal anisotropy beneath Tibet: evidence for co-existing channel flow and pure-shear crustal thickening

Crustal and upper mantle structure beneath the northeastern Tibetan Plateau from joint analysis of receiver functions and Rayleigh wave dispersions

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