Abstract
<p>Through inversion of fundamental mode group velocities of Love and Rayleigh waves, we study the crustal and subcrustal structure across the central Deccan Volcanic Province (DVP), which is one of the world’s largest terrestrial flood basalts. Our analysis is based on broadband seismograms recorded at seismological station Bhopal (BHPL) in the central India from earthquakes located near west coast of India, with an average epicentral distance about 768 km. The recording station and epicentral zone are situated respectively on the northern and southern edges of DVP with wave paths across central DVP. The period of group velocity data ranges from 5 to 60 s for Rayleigh waves and 5 to 45 s for Love waves. Using the genetic algorithm, the observed data have been inverted to obtain the crust and subcrustal velocity structure along the wavepaths. Using this procedure, a similar velocity structure was also obtained earlier for the northwestern DVP, which is in the west of the present study region. Comparison of results show that the crustal thickness decreases westward from central DVP (39.6 km) to northwestern DVP (37.8 km) along with the decrease of thickness of upper crust; while the thickness of lower crust remains nearly same. From east to west S-wave velocity in the upper crust decreases by 2 to 3 per cent, while P-wave velocity in the whole crust and subcrust decreases by 3 to 6 per cent. The P- and S-wave velocities are positively correlated with crustal thickness and negatively correlated with earth’s heat flow. It appears that the elevated crustal and subcrustal temperature in the western side is the main factor for low velocities on this side.</p>
Highlights
The Deccan Volcanic Province (DVP) is the most remarkable continental flood basalts provinces of the Indian Peninsula and formed around 65 My, when this region passed over the Reunion hotspot during its northward movement [Duncan and Pyle 1988]
Reviewing the surface wave studies in the Indian Peninsula, Bhattacharya [1992] noted that the short period (0.6 to 2.5 s) surface wave data across the Koyna region are satisfied by IP12 (Figure 2); IP12 is same as IP11 except the top 1 km of latter is replaced by a Deccan trap layer
(1) The crustal thickness of central DVP is 39.6 km, which remains in the range between 38.7 and 40.2 km obtained in other areas of the central India
Summary
The Deccan Volcanic Province (DVP) is the most remarkable continental flood basalts provinces of the Indian Peninsula and formed around 65 My, when this region passed over the Reunion hotspot during its northward movement [Duncan and Pyle 1988]. Singh et al [1999] obtained velocity structure using surface waves recorded at regional distances from 1997 Jabalpur earthquake in the central India (Figure 2). The crustal structure of northwestern DVP was obtained by Prajapati et al [2011] using observed surface wave dispersion of Rayleigh and Love waves along a few wavepaths across this region. 2. Data and measurement of group velocity To select surface wavepaths across central-DVP, we consider the broadband records of the station Bhopal (BHPL), which is located in the northern part of DVP and analyze earthquakes occurred in the Koyna region in the west coast of India (Figure 1). The theoretical group velocity curves for different structures (Figure 3) of the Indian Peninsula are compared with the present mean observed data across central DVP. The misfit for this model is 0.77; this misfit value shows that the theoretical curves are within the SD of the observed data
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