Crustal Structure of the Western Bengal Basin from Joint Analysis of Teleseismic Receiver Functions and Rayleigh-Wave Dispersion

Abstract

Teleseismic data recorded at the broadband seismological observatory of the Indian Institute of Technology (IIT) Kharagpur are analyzed to determine the seismic characteristics of the crust beneath the western Bengal basin. Receiver functions calculated from the teleseismic P waveform for a range of back azimuths show little variation in the Moho Ps arrival time, indicating a nearly one-dimensional crustal structure beneath Kharagpur. Transforming the time domain receiver functions into the H-V p =V s domain for a stack of all receiver functions reveals a 38 2 km thick crust with a V p =V s of 1:73 0:01. Receiver functions stacked in narrow bins of back azimuth and great-circle-arc distance were inverted jointly with group velocity dispersion data for periods from 15 to 45 sec. Joint inversion results reveal a near surface sedimentary layer of ∼1:5 km thickness, a 13 km thick upper crust, and a 23 km thick lower crust with the Moho at a depth of ∼37:5 km. The average crustal S-wave velocity is 3:7 km=sec. The top 0.5 km of the sedimentary layer has very low S-wave velocity and a large impedance contrast with the underlying layer. This represents the thin layer of unconsolidated sediments and weathered laterites near the surface as seen from deep seismic sounding (DSS) studies across the region.The S-wave velocity structure of the crust beneath Kharagpur is the first such result for the western Bengal basin and is broadly similar to that of the Indian Shield crust. A comparison of the crustal thickness and lower crustal velocities between Kharagpur and Agartala, seperated by the Eocene hinge zone, shows remarkable differences. Crustal models beneath Agartala reveal ∼36 km thick crust with the pres

Site-Specific Modeling of SH and P-SV Waves for Microzonation Study of Kolkata Metropolitan City, India

“…MITRA et al, (2008) show, at very shallow depth, the very sharp increase in S-wave velocity that is visible in our section models.…”

“…The BB 0 (4 km), CC 0 (4.5 km) and DD 0 (4.5 km) profiles run through the length of the metro track with a total length of 13 km from the Tollygunj to Shyam Bazar station and reach a depth of 60 m. The mechanical properties of S-wave velocity (V s ), density (q) and the quality factor (Q p and Q s ) for the local structural model of various soil layers along each profile are shown in Tables 1 and 2. The 2D structural model used for computation is a realistic model which reflects the sharp jump in the S-wave velocity (V s ) followed by a continuous 1D structure model (MITRA et al, 2008). In the computation for BB 0 , CC 0 and DD 0 , we have merged the very thin topmost layer with the layer below, to avoid digitization problems.…”

Crustal Structure and Evolution of the Eastern Himalayan Plate Boundary System, Northeast India

“…To the south of the plateau, due to change in crustal structure (from continental to transitional) and flexure of the crust, the passive margin normal faults got reactivated as reverse/thrust faults. Farther west beneath the Western Bengal Basin, receiver function models have revealed continental crust overlying a thin veneer of fluvial sediments (Mitra et al, 2008). The Oldham Fault, a south dipping back thrust, to the north dipping Dawki Fault (Clark & Bilham, 2008) could have been activated subsequently to accommodate the flexural bending of the underthrust Indian lithosphere to the north (England & Bilham, 2015).…”

Seismotectonics of the eastern Himalayan and indo-burman plate boundary systems

“…The associated slip vectors are parallel to the Eocene hinge zone (Figure b). The thick pile of overlying sediments form the thickest continental sedimentary basin (∼20 km) and are known to be oversaturated (from V p / V s estimate using receiver functions) [ Mitra et al , , ]. It is conjectured that the sedimentary layer has very low shear strength and deforms by aseismic creep, except for the region within the Tripura fold‐thrust belt.…”