Anisotropic Structure beneath the Indian Continent from Surface wave studies
Abstract
The shear wave splitting measurements have conclusively demonstrated that plate motion related strain is the dominant mechanism for forging the anisotropic character of the Indian plate (Kumar and Singh, 2008; Saikia et al., 2010). Forward modelling of the variability of splitting parameters with incoming polarization reveals two layers of anisotropy beneath the Indian shield. A stronger anisotropy (δt 1s) in the bottom layer is related to asthenospheric flow and a weaker one (δt 0.4s) in the upper layer possibly represents anisotropy frozen in the lithosphere. However, depth localization of anisotropic structures beneath India are poorly known. In the present study, we collated a new seismic dataset to investigate the 3-D anisotropic structure of the upper mantle beneath the Indian continent. We measured surface wave dispersion (group and phase) curves amounting to 14,000 Rayleigh and 6,000 Love waves and inverted them to obtain isotropic SV-wave velocity (VSV), azimuthal (G, ψG) and radial anisotropies (ξ) down to 300km. The lateral resolution of our tomography model is 200km, which is uniform in most of the study area except the western part, where data coverage is poor. We observe 2 to 3% radial anisotropy in top 100km beneath the central to southern region of the continent. On the other hand, we observe a significant change in the direction of azimuthal anisotropy with evidence for two-layers ( 80-110km and 150-250km) especially beneath cratons, in agreement with the interpretation of SKS splitting. The three resolved parameters (VSV, ξ, ψG) derived from the tomography model show presence of an intermediate layer ( 80-110km) within the cratonic lithosphere, which can be interpreted as an MLD. Our study images the LAB beneath the Indian cratons with both isotropic (VSV) and anisotropic parameters (ψG). We observed large variations (120-250km) in the LAB beneath Indian continent with the thickest lithospheric cratonic keels beneath central India.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.S43B2830M
- Keywords:
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- 3260 Inverse theory;
- MATHEMATICAL GEOPHYSICSDE: 3275 Uncertainty quantification;
- MATHEMATICAL GEOPHYSICSDE: 7270 Tomography;
- SEISMOLOGYDE: 7290 Computational seismology;
- SEISMOLOGY