The early Cretaceous thermal perturbation beneath the eastern continental margin of the Indian shield resulted in the eruption of the Rajmahal Traps. To understand the impact of the magmatic process that originated in the deep mantle on the lower crustal level of the eastern Indian shield and adjoining Bengal basin the conspicuous gravity anomalies observed over the region have been modelled integrating with available geophysical information. The 3-D gravity modelling has delineated 10–15 km thick high-density (ρ = 3.02 g/cm³) accreted igneous layer at the base of the crust beneath the Rajmahal Traps. Thickness of this layer varies from 16 km to the west of the Rajmahal towards north to about 12 km near Kharagpur towards south and about 18 km to the east of the Raniganj in the central part of the region. The greater thickness of the magmatic body beneath the central part of the region presents itself as the locus of the potential feeder channel for the Rajmahal Traps. It is suggested that the crustal accretion is the imprint of the mantle thermal perturbation, over which the eastern margin of the eastern Indian shield opened around 117 Ma ago. The nosing of the crustal accretion in the down south suggests the possible imprint of the subsequent magmatic intrusion along the plume path.

We analyzed 3365 relocated aftershocks with magnitude of completeness (Mc) ≥ 1.7 that occurred in the Kachchh Rift Basin (KRB) between August 2006 and December 2010. The analysis of the new aftershock catalogue has led to improved understanding of the subsurface structure and of the aftershock behaviour. We characterized aftershock behaviour in terms of 𝑎-value, 𝑏-value, spatial fractal dimension ($D_s$), and slip ratio (ratio of the slip that occurred on the primary fault and that of the total slip). The estimated 𝑏-value is 1.05, which indicates that the earthquake occurred due to active tectonics in the region. The three dimensional 𝑏-value mapping shows that a high 𝑏-value region is sandwiched around the 2001 Bhuj mainshock hypocenter at depths of 20–25 km between two low 𝑏-value zones above and below this depth range. The $D_s$-value was estimated from the double-logarithmic plot of the correlation integral and distance between hypocenters, and is found to be 2.64 ± 0.01, which indicates random spatial distribution beneath the source zone in a two-dimensional plane associated with fluid-filled fractures. A slip ratio of about 0.23 reveals that more slip occurred on secondary fault systems in and around the 2001 Bhuj earhquake (Mw 7.6) source zone in KRB.