Role of crustal structure in geodynamic evolution and seismogenesis in the eastern Indo-Gangetic Foreland Basin and Himalayan collision zone

The incessant convergence between the Indian and Eurasian plates has significantly altered the crustal thicknesses of the Indian subcontinent since their collision and formed one of the most dynamically active geological provinces in the northern Indian subcontinent, namely the Indo-Gangetic Foreland Basin (IGFB). The crustal geometry of this segment of the Indian Plate has long been a primary research focus due to the frequent occurrence of devastating earthquakes in the region. In this context, we aim to map the crustal layers of the eastern IGFB to establish a realistic and widely accepted framework for understanding its tectonogenesis. In this study, derivative analysis of the Bouguer Anomaly (BA) was used to delineate the E-W trending basement-controlled subsurface geological structures formed during the Miocene and Pleistocene epochs. The depths of the Precambrian basement and the Moho discontinuity range from 1 to 6.8 km and 39-60 km, respectively. Forward modelling of the BA reveals that the crustal interfaces beneath the eastern IGFB dip steeply northward, which is primarily associated with the Himalayan orogeny during the Eocene and Pleistocene epochs. The findings of this study indicate that the Munger-Saharsa Ridge (MSR) has controlled subsidence in the eastern IGFB from the Miocene to the present day. Furthermore, this study has identified a blind fault in the Gandak depression, where fault activity may be driven by either the southward propagation of the Himalayan wedge or by compressional bending of the lower crust. We also propose that the Munger-Saharsa Ridge, in conjunction with crustal bending, plays a significant role in modulating seismicity in the eastern segment of the IGFB.