Letter | Published:

Imaging the Indian subcontinent beneath the Himalaya

Abstract

The rocks of the Indian subcontinent are last seen south of the Ganges before they plunge beneath the Himalaya and the Tibetan plateau. They are next glimpsed in seismic reflection profiles deep beneath southern Tibet1, yet the surface seen there has been modified by processes within the Himalaya that have consumed parts of the upper Indian crust and converted them into Himalayan rocks2,3. The geometry of the partly dismantled Indian plate as it passes through the Himalayan process zone has hitherto eluded imaging. Here we report seismic images both of the decollement at the base of the Himalaya and of the Moho (the boundary between crust and mantle) at the base of the Indian crust. A significant finding is that strong seismic anisotropy develops above the decollement in response to shear processes that are taken up as slip in great earthquakes at shallower depths. North of the Himalaya, the lower Indian crust is characterized by a high-velocity region consistent with the formation of eclogite, a high-density material whose presence affects the dynamics of the Tibetan plateau.

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Acknowledgements

We thank C. Jones and P. Molnar for comments; H. Gilbert, F. Blume, R. Bendick, the Department of Mines and Geology of Nepal, particularly R. K. Aryal and N. R. Shtapit, and the Chinese Academy of Sciences, in particular H. B. Liu, for their collaboration and assistance; the US National Science Foundation for support; and the Incorporated Research Institutions for Seismology for use of their instruments. Author Contributions V.S., A.S., S.S., M..P., R.B. and F.W. participated in the deployment and data collection. V.S., G.M. and A.S. performed the seismological analysis. S.S., R.B. and F.W. provided the tectonic and geological context. V.S. wrote the Letter with contributions from all authors.

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Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Correspondence to Vera Schulte-Pelkum.

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Supplementary Notes

This contains Supplementary Methods, Supplementary Tables S1 and S2, and Supplementary Figures S1-S4. (PDF 249 kb)

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Further reading

Figure 1: Location map.
Figure 2: Receiver function analysis along profile and interpretation.
Figure 3: Observed and synthetic data showing the anisotropic shear zone, and explanation.

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