SN Bhattacharya - Profile on Academia.edu (original) (raw)
Uploads
Papers by SN Bhattacharya
Annals of Geophysics, 2014
Through inversion of fundamental mode group velocities of Love and Rayleigh waves, we study the c... more 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 ...
Annals of Geophysics, 2015
We measure the inter-station Rayleigh and Love wave phase velocities across the northwestern Indi... more We measure the inter-station Rayleigh and Love wave phase velocities across the northwestern Indian Peninsular shield (NW-IP) through cross-correlation and invert these velocities to evaluate the underneath crust and upper mantle velocity structure down to 400 km. We consider a cluster of three stations in the northern tip of the Peninsula and another cluster of eight stations in the south. We measure phase velocities along 28 paths for Rayleigh waves and 17 paths for Love waves joining two stations with one from each cluster and using broadband records of earthquakes which lie nearly on the great circle joining the pair of stations. The phase velocities are in the period range of 10 to 275 s for Rayleigh waves and of 10 to 120 s for Love waves. The isotropic model obtained through inversion of the phase velocities indicates 199.1 km thick lithosphere with 3-layered crust of thickness 36.3 km; the top two layers have nearly same velocities and both constitute the upper crust with th...
Annals of Geophysics, 2015
Sensitivity kernels or partial derivatives of phase velocity (c) and group velocity (U) with resp... more Sensitivity kernels or partial derivatives of phase velocity (c) and group velocity (U) with respect to medium parameters are useful to interpret a given set of observed surface wave velocity data. In addition to phase velocities, group velocities are also being observed to find the radial anisotropy of the crust and mantle. However, sensitivities of group velocity for a radially anisotropic Earth have rarely been studied. Here we show sensitivities of group velocity along with those of phase velocity to the medium parameters VSV, VSH , VPV, VPH , h and density in a radially anisotropic spherical Earth. The peak sensitivities for U are generally twice of those for c; thus U is more efficient than c to explore anisotropic nature of the medium. Love waves mainly depends on VSH while Rayleigh waves is nearly independent of VSH . The sensitivities show that there are trade-offs among these parameters during inversion and there is a need to reduce the number of parameters to be evaluated...
Annals of Geophysics, Dec 21, 2017
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.
Crustal Structure of the Western Bengal Basin from Joint Analysis of Teleseismic Receiver Functions and Rayleigh-Wave Dispersion
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. ...
Annals of Geophysics, 2014
Through inversion of fundamental mode group velocities of Love and Rayleigh waves, we study the c... more 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 ...
Annals of Geophysics, 2015
We measure the inter-station Rayleigh and Love wave phase velocities across the northwestern Indi... more We measure the inter-station Rayleigh and Love wave phase velocities across the northwestern Indian Peninsular shield (NW-IP) through cross-correlation and invert these velocities to evaluate the underneath crust and upper mantle velocity structure down to 400 km. We consider a cluster of three stations in the northern tip of the Peninsula and another cluster of eight stations in the south. We measure phase velocities along 28 paths for Rayleigh waves and 17 paths for Love waves joining two stations with one from each cluster and using broadband records of earthquakes which lie nearly on the great circle joining the pair of stations. The phase velocities are in the period range of 10 to 275 s for Rayleigh waves and of 10 to 120 s for Love waves. The isotropic model obtained through inversion of the phase velocities indicates 199.1 km thick lithosphere with 3-layered crust of thickness 36.3 km; the top two layers have nearly same velocities and both constitute the upper crust with th...
Annals of Geophysics, 2015
Sensitivity kernels or partial derivatives of phase velocity (c) and group velocity (U) with resp... more Sensitivity kernels or partial derivatives of phase velocity (c) and group velocity (U) with respect to medium parameters are useful to interpret a given set of observed surface wave velocity data. In addition to phase velocities, group velocities are also being observed to find the radial anisotropy of the crust and mantle. However, sensitivities of group velocity for a radially anisotropic Earth have rarely been studied. Here we show sensitivities of group velocity along with those of phase velocity to the medium parameters VSV, VSH , VPV, VPH , h and density in a radially anisotropic spherical Earth. The peak sensitivities for U are generally twice of those for c; thus U is more efficient than c to explore anisotropic nature of the medium. Love waves mainly depends on VSH while Rayleigh waves is nearly independent of VSH . The sensitivities show that there are trade-offs among these parameters during inversion and there is a need to reduce the number of parameters to be evaluated...
Annals of Geophysics, Dec 21, 2017
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.
Crustal Structure of the Western Bengal Basin from Joint Analysis of Teleseismic Receiver Functions and Rayleigh-Wave Dispersion
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. ...