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Solid Earth An interactive open-access journal of the European Geosciences Union

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doi:10.5194/se-2016-134
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
20 Sep 2016
Review status
A revision of this discussion paper was accepted for the journal Solid Earth (SE) and is expected to appear here in due course.
Seismic anisotropy inferred from direct S-waves derived splitting measurements and its geodynamic implications beneath southeastern Tibetan Plateau
Ashwani Kant Tiwari1, Arun Singh1, Tuna Eken2, Nitin Grewal1, and Chandrani Singh1 1Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, India
2Department of Geophysical Engineering, Istanbul Technical University, Turkey
Abstract. The present study deals with detecting seismic anisotropy parameters beneath southeastern Tibet near Namche Barwa Mountain using splitting of the direct S-waves. We employed the reference station technique to remove the effects of source side anisotropy. Seismic anisotropy parameters, splitting time delay and fast polarization directions were estimated through analyses on a total of 501 splitting measurements obtained from direct-S waves from 25 earthquakes (> 5.5 magnitude) that were recorded at 42 stations of Namchebarwa seismic network. We observed a large variation in time delays ranging from 0.64 to 1.68 s but in most cases it is more than 1 s, which suggests for a highly anisotropic lithospheric mantle in the region. A comparison between direct S- and SKS-derived splitting parameters generally shows a close similarity although some discrepancies exist where null or negligible anisotropy is reported earlier using SKS. The seismic stations with hitherto null or negligible anisotropy are now supplemented with new measurements with clear anisotropic signatures. Our analyses indicate a sharp change in lateral variations of fast polarization directions (FPDs) from consistent ENE-SSW or E-W to NW-SE direction at the southeastern edge of Tibet. Comparison of the FPDs with global positioning system (GPS) measurements, absolute plate motion (APM) directions and surface geological features signify that the observed anisotropy and hence inferred deformation patterns are not only due to asthenospheric dynamics but it is a combination of lithospheric deformation and sub-lithospheric (asthenospheric) mantle dynamics. Splitting measurement using direct-S waves proves their utility to supplement the anisotropic measurements in the study region and fills the missing links that remain rather illusive due to lack of SKS measurements.

Citation: Tiwari, A. K., Singh, A., Eken, T., Grewal, N., and Singh, C.: Seismic anisotropy inferred from direct S-waves derived splitting measurements and its geodynamic implications beneath southeastern Tibetan Plateau, Solid Earth Discuss., doi:10.5194/se-2016-134, in review, 2016.
Ashwani Kant Tiwari et al.
Ashwani Kant Tiwari et al.

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Short summary
New splitting measurements are obtained using direct-S waves by correcting source side contamination using data from southeastern Tibetan near Namche Barwa Mountains. A highly deformed lithospheric and sub-lithospheric mantle reveals fast-axis patterns close to the surficial expressions of the local geology. Significant anisotropy observed at stations where null of no measurements were obtained in earlier studies signifies the importance of using direct-S waves for anisotropic measurements.
New splitting measurements are obtained using direct-S waves by correcting source side...
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