Delineation of shallow structure and the Gondwana graben in the Mahanadi delta, India, using forward modeling of first arrival seismic data

Evidence of underplating from seismic and gravity studies in the Mahanadi delta of eastern India and its tectonic significance

“…Fluids released during the process of magmatism may get trapped at some depth, and this may have formed the low‐velocity (6.0 km/s) and low‐density (2.65 g/cm 3 ) layer at the midcrustal level. A thin (∼200 m) lid of high‐velocity (5.5 km/s) volcanic rock at very shallow depth (∼150 m) underlain by a thick (∼1.75 km) pile of Gondwana sediments [ Behera et al , 2002; Behera , 2003] may represent the sill‐type structure (Figure 19). This indicates intense volcanism that has affected the entire crustal column in the form of undulating intracrustal boundaries including the Moho.…”

“…The velocity-depth images of the crustal models are shown in Figure 8. Note that the shallow velocity variation (1.7 -5.0 km/s) down to the basement [Behera et al, 2002;Behera, 2003] is not shown here to expand the crustal velocity variations between 5.0 and [Sain and Kaila, 1994]. The travel times are plotted in a reduced timescale with a reduction velocity of 7.0 km/s.…”

“…The velocity‐depth images of the crustal models are shown in Figure 8. Note that the shallow velocity variation (1.7–5.0 km/s) down to the basement [ Behera et al , 2002; Behera , 2003] is not shown here to expand the crustal velocity variations between 5.0 and 8.0 km/s. The final velocity models are derived on the basis of (1) minimum RMS travel time residual between the data and the model response, (2) ability to trace rays to almost all observations, (3) parameterization represented by minimum number of velocity and boundary nodes, and (4) high parameter resolution.…”

“…The shot interval is ∼10 km, whereas the average receiver interval is 400–500 m after digitization. The shallow structure down to the basement was modeled using the first‐arrival refraction data [ Behera et al , 2002; Behera , 2003]. The most important aspects of modeling are the phase identification and classification.…”

“…They were juxtaposed with the Amery ice shelf, Prydz Bay, and adjoining regions of Antarctica. The coastal part of the Mahanadi basin and the continental shelf is characterized by Early Cretaceous and older Gondwana sediments overlain by volcanic rocks [ Behera et al , 2002], which are considered contemporary to the Rajmahal, Bengal, and Sylhet traps [ Fuloria , 1993; Mishra , 1984; Baksi , 1995]. This indicates that the Mahanadi rift resembles an active continental rift with magmatic activities along the coastal part and the continental shelf to the Lambert rift and Prydz Bay of Antarctica (Figure 18).…”