High Resolution Rayleigh Wave Group Velocity Tomography of South India.

We present a comprehensive study of Rayleigh wave group velocity tomography in South India. South India is a stable continent comprising of Precambrian terrains such as the eastern Dharwar craton (EDC), the western Dharwar craton (WDC), the southern Granulite terrain (SGT), and the Cuddapah basin. The data used for the analysis were recorded at 51 broadband stations operated during 2009-2012 across this region. Based on the analysis a total of 781 unique earthquake events with shallow or moderate depths were chosen having an epicentral distance of 5^o-30^o and magnitude M_s ≥ 4.5. This attributed to a total of 4873 source-station raypaths for which the dispersion curves were calculated to obtain Rayleigh-wave group velocity maps in the period 10-200 secs. Due to the high ray coverage over the southern terrain, we obtained a high resolution of 0.5^o-1^o across all time periods. Furthermore, the local group velocity dispersion curve obtained for each grid cell were inverted for shear wave velocity profile. The tomographic velocity image reveals thinner crust ( 35 Km) in the late Archaen ( 2.7 Ga) EDC and relatively higher ( 40-50 Km) in adjoining terrains (mid-Archean and Proterozoic). The mid-Archaen ( 3.36 Ga) WDC has a thicker crust ( 50 Km). The depth versus velocity profile information obtained from inversion gives a quantitative picture of the lithospheric root around this entire terrain of Southern India.