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Papers by SN Bhattacharya

Bulletin of the Seismological Society of America, 2009

Interstation phase velocities of surface waves are measured through a cross-correlation method ac... more Interstation phase velocities of surface waves are measured through a cross-correlation method across the Bastar craton in the eastern part of the Indian peninsula. The periods of Love waves lie between 15 and 91 sec and those of Rayleigh waves lie between 13 and 104 sec. The observed phase velocities are close to the theoretical dispersion curves for the crust and upper mantle structure IP11 obtained earlier for central India (in the Indian peninsula) through inversion of surface-wave group velocities. However, for periods higher than 70 sec, the theoretical curves remain above the observed data. In IP11, the upper mantle low velocity zone (LVZ) starts downward at a depth of 140 km; the S-wave velocity (V S) in the LVZ of IP11 is decreased based on the recent studies, and the modified structure IP11L is obtained. The theoretical dispersion curves of IP11L improve the fit to the observed data particularly at higher periods. The lithospheric part of IP11L is then improved through genetic algorithm inversion with more stratification in the structure for a better fit to the observed data. Such inversion generated the model IP11BA for the Bastar craton. The crustal thickness of this craton is found to be 40:1 0:6 km with the thickness of the upper crust as 15:3 0:7 km, which is less than the corresponding thickness of 20 km in southern India. In the upper crust, V S shows a small increase with depth, having an average value of 3:508 km=sec, and in the lower crust, V S 3:934 km=sec. These values of V S for the crust of the Bastar craton are nearly the same as those found in southern India. Below the Moho down to a depth of 70 km, IP11BA shows a constant V S of 4:577 km=sec and then increases slowly to 4:609 km=sec at the top of the LVZ.

Bulletin of the Seismological Society of America, 2011

The lithospheric velocity structure of the lower Indus basin has been evaluated through inversion... more The lithospheric velocity structure of the lower Indus basin has been evaluated through inversion of fundamental modes of both Love and Rayleigh wave group velocities from the broadband records of a seismic network maintained by the Institute of Seismological Research, Gujarat, India. We have considered three clusters of wave paths A, B, and C that mainly cross the lower Indus basin from south to north; the wave paths of A mainly cross the continental shelf, and the wave paths of B and C pass through the lower Indus basin. The measured group velocities correspond to periods of 5 to 90 s for Rayleigh waves, and 5 to 115 s for Love waves. These data sets resolve the structure of the lithosphere through a nonlinear inversion based on a genetic algorithm with a wide solution space. The mean and standard deviation (S.D.) of the 70 accepted solutions for each of these three clusters provide the 2D structure for the lower Indus basin from south to north. The sediment consists of two layers with total thickness from 5.7 to 6.6 km increasing northward. The crustal thickness also increases northward from 32.9 (cluster A) to 39.7 km (cluster C) in the lower Indus region. The S-wave velocity below the crust varies from 4.55 to 4:59 km=s, which is close to the corresponding velocity of 4:60 km=s of the Indian shield region to the east of the Aravalli range. The thicknesses of the lithosphere, as well as the velocities of the uppermost mantle of the lower Indus plain, are similar to that of the Indian shield.

Pure and Applied Geophysics PAGEOPH, 1996

We consider the second-order differential equations of P-SV motion in an isotropic elastic medium... more We consider the second-order differential equations of P-SV motion in an isotropic elastic medium with spherical coordinates. We assume that in the medium Lam6's parameters 2, # oc r p and compressional and shear-wave velocities c~, flocr, where r is radial distance. With this regular heterogeneity both the radial functions appearing in displacement components satisfy a fourth-order differential equation which provides solutions in terms of exponential functions. We then consider a layered spherical earth in which each layer has heterogeneity as specified above. The dispersion equation of the Rayleigh wave is obtained using the Thomson-Haskel method. Due to exponential function solutions in each layer, the dispersion equation has similar simplicity as in a flat-layered earth. The dispersion equation is further simplified when p =-2. We obtain numerical results which agree with results obtained by other methods.

Bulletin of the Seismological Society of America, 2008

... Moreover, results obtained from previous studies of deep seismic refraction, wide-angle refle... more ... Moreover, results obtained from previous studies of deep seismic refraction, wide-angle reflection (Kaila et al., 1992; Sarkar et al., 1995; Kaila et al., 1996; Reddy et al ... We thank Probal Sengupta for support in maintaining the Kharagpur Broadband Observatory and data archival. ...

Bulletin of the Seismological Society of America, 2009

Interstation phase velocities of surface waves are measured through a cross-correlation method ac... more Interstation phase velocities of surface waves are measured through a cross-correlation method across the Bastar craton in the eastern part of the Indian peninsula. The periods of Love waves lie between 15 and 91 sec and those of Rayleigh waves lie between 13 and 104 sec. The observed phase velocities are close to the theoretical dispersion curves for the crust and upper mantle structure IP11 obtained earlier for central India (in the Indian peninsula) through inversion of surface-wave group velocities. However, for periods higher than 70 sec, the theoretical curves remain above the observed data. In IP11, the upper mantle low velocity zone (LVZ) starts downward at a depth of 140 km; the S-wave velocity (V S) in the LVZ of IP11 is decreased based on the recent studies, and the modified structure IP11L is obtained. The theoretical dispersion curves of IP11L improve the fit to the observed data particularly at higher periods. The lithospheric part of IP11L is then improved through genetic algorithm inversion with more stratification in the structure for a better fit to the observed data. Such inversion generated the model IP11BA for the Bastar craton. The crustal thickness of this craton is found to be 40:1 0:6 km with the thickness of the upper crust as 15:3 0:7 km, which is less than the corresponding thickness of 20 km in southern India. In the upper crust, V S shows a small increase with depth, having an average value of 3:508 km=sec, and in the lower crust, V S 3:934 km=sec. These values of V S for the crust of the Bastar craton are nearly the same as those found in southern India. Below the Moho down to a depth of 70 km, IP11BA shows a constant V S of 4:577 km=sec and then increases slowly to 4:609 km=sec at the top of the LVZ.

Bulletin of the Seismological Society of America, 2011

The lithospheric velocity structure of the lower Indus basin has been evaluated through inversion... more The lithospheric velocity structure of the lower Indus basin has been evaluated through inversion of fundamental modes of both Love and Rayleigh wave group velocities from the broadband records of a seismic network maintained by the Institute of Seismological Research, Gujarat, India. We have considered three clusters of wave paths A, B, and C that mainly cross the lower Indus basin from south to north; the wave paths of A mainly cross the continental shelf, and the wave paths of B and C pass through the lower Indus basin. The measured group velocities correspond to periods of 5 to 90 s for Rayleigh waves, and 5 to 115 s for Love waves. These data sets resolve the structure of the lithosphere through a nonlinear inversion based on a genetic algorithm with a wide solution space. The mean and standard deviation (S.D.) of the 70 accepted solutions for each of these three clusters provide the 2D structure for the lower Indus basin from south to north. The sediment consists of two layers with total thickness from 5.7 to 6.6 km increasing northward. The crustal thickness also increases northward from 32.9 (cluster A) to 39.7 km (cluster C) in the lower Indus region. The S-wave velocity below the crust varies from 4.55 to 4:59 km=s, which is close to the corresponding velocity of 4:60 km=s of the Indian shield region to the east of the Aravalli range. The thicknesses of the lithosphere, as well as the velocities of the uppermost mantle of the lower Indus plain, are similar to that of the Indian shield.

Pure and Applied Geophysics PAGEOPH, 1996

We consider the second-order differential equations of P-SV motion in an isotropic elastic medium... more We consider the second-order differential equations of P-SV motion in an isotropic elastic medium with spherical coordinates. We assume that in the medium Lam6's parameters 2, # oc r p and compressional and shear-wave velocities c~, flocr, where r is radial distance. With this regular heterogeneity both the radial functions appearing in displacement components satisfy a fourth-order differential equation which provides solutions in terms of exponential functions. We then consider a layered spherical earth in which each layer has heterogeneity as specified above. The dispersion equation of the Rayleigh wave is obtained using the Thomson-Haskel method. Due to exponential function solutions in each layer, the dispersion equation has similar simplicity as in a flat-layered earth. The dispersion equation is further simplified when p =-2. We obtain numerical results which agree with results obtained by other methods.

Bulletin of the Seismological Society of America, 2008

... Moreover, results obtained from previous studies of deep seismic refraction, wide-angle refle... more ... Moreover, results obtained from previous studies of deep seismic refraction, wide-angle reflection (Kaila et al., 1992; Sarkar et al., 1995; Kaila et al., 1996; Reddy et al ... We thank Probal Sengupta for support in maintaining the Kharagpur Broadband Observatory and data archival. ...