HR: 10:20h
AN: T22D-01    [Abstracts]
TI: Crust And Upper Mantle Structure Of The Bengal Basin And Bay Of Bengal From Surface Wave Group Velocity Dispersion Studies
AU: Dhali, K K
EM: kishoreiitkgp@yahoo.co.in
AF: Dept. Geology and Geophysics, Indian Institute of Technology, Kharagpur, WB 721302, India
AU: Majhi, S
EM: mitra@iitkgp.ac.in
AF: Dept. Geology and Geophysics, Indian Institute of Technology, Kharagpur, WB 721302, India
AU: * Mitra, S
EM: mitra@gg.iitkgp.ernet.in
AF: Dept. Geology and Geophysics, Indian Institute of Technology, Kharagpur, WB 721302, India
AU: Priestley, K
EM: keith@madingley.org
AF: Bullard Laboratory, Dept. of Earth Sciences, Madingley Rise Cammridge University, Cambridge, CB30EZ, United Kingdom
AB: Fundamental mode Rayleigh and Love wave group velocity dispersion for paths crossing the Bay of Bengal have been calculated for earthquakes in the Indo-Burman arc and the Andaman-Sumatra subduction zone recorded at seismographs in the eastern part of Peninsula India and Sri Lanka. The ray-path coverage in this study provides a better spatial sampling than any previous studies of the region. The individual dispersion curves range from 12 to 70~s and have been clustered in four spatial groups to form average dispersion curves representative of the Bengal basin, northern, central and southern Bay of Bengal. These average dispersion curves for Rayleigh and Love waves are jointly inverted to obtain shear wave velocity structure of the lithosphere. The higher frequencies/shorter periods (12--30~s) used in the inversion constrains the sediment shear wave speed and thickness while the longer periods provide information of the upper mantle structure. The results show a remarkable increase in the sediments thickness along the Bengal Fan from south to north ranging from 6 km, around the southern tip of India, to 23 km beneath the Bengal basin. The shear wave velocity models reveal a sediment saturation beyond 7-10 km of burial leading to metamorphism and eventual increase in velocity to continent like material with depth. The average crustal thickness (loose sediments overlying consolidated sediments followed by metasediments and oceanic crust) is anomalously continental (~20-36 km) rather than being simply oceanic crust overlain by sediments. The average shear wave velocity is about 3.5-3.8 km/s which is more representative of continental crusts. Finally the low velocity zone in the uppermost mantle is possibly an effect of the expected increase in temperature due to blanketing of the fan sediments over the Bay of Bengal crust. The misfits to parts of the dispersion data using a 1D isotropic model provides an indication of the presence of polarization anisotropy in the lithosphere and sets a good starting point for modeling the anisotropic structure.
DE: 7220 Oceanic crust
DE: 7255 Surface waves and free oscillations
DE: 8100 TECTONOPHYSICS
DE: 9320 Asia
SC: Tectonophysics [T]
MN: 2007 Fall Meeting