Shear-wave splitting unmasks deformation properties in the Eastern Himalayan Syntaxis and Namcha Barwa region
Abstract
The Himalayan orogen and the Tibetan Plateau resulted from the collision between the Indian Plate and Eurasian Plate. This young and active orogenic system provides excellent opportunities to examine the lithospheric deformation and various dynamic processes during continental collision. Of particular interest is the Eastern Himalayan Syntaxis, where the structures of the Himalayan range change abruptly, developing an 'indenter corner' at the edge of the two colliding plates. Previous GPS measurements in the broad areas of Tibet and the adjacent Sichuan Basin reveal a clockwise deformation pattern. These observations have led to the crustal flow model, among others, suggesting that the lower crust beneath Tibet is weak and thus moving toward southeast during the collision. However, it is unclear to what extent the surface deformation detected by GPS can represent the deformation and flow pattern in the underlying lithosphere. Seismic anisotropy, on the other hand, offers an effective means to infer the lithospheric deformation. The past decade has seen a series of deployments of broadband seismic arrays in the Himalaya-Tibet and surrounding regions that yield shear-wave splitting measurements indicating complexities in anisotropic parameters in this region. In this study, we perform shear-wave splitting analysis of teleseismic waveform data from 25 recently deployed broadband stations in the Namcha Barwa region. The analysis was operated on the SKS phase that travels through the Earth's core from the mantle, which is then radially polarized upon reentry. We apply a particle motion test with the cross-correlation method, in which the values of the rotation direction (phi) and the time lag (dt) are selected when the cross-correlation coefficient attains its maximum. Our preliminary results show a general NE-SW (61-66 degrees) fast axis of polarization direction to the west of Yarlung-Tsangpo River. The polarization direction appears to be roughly parallel to that of the Indian absolute plate motion. To the farther east, the fast axis wraps around the edge of the Himalayan syntaxis with a NW-SE orientation. Most of the stations yield delay times between 0.10 and 0.425 s, much lower compared to those obtained in the surrounding regions, suggesting possibly weaker anisotropy in this region. Nevertheless, our observations may argue for a mechanically coupled crust and lithospheric mantle at the suture region.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMDI11A2169C
- Keywords:
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- 7218 SEISMOLOGY Lithosphere;
- 8104 TECTONOPHYSICS Continental margins: convergent;
- 8120 TECTONOPHYSICS Dynamics of lithosphere and mantle: general