Crustal Configuration and Seismic Stability of the Eastern Indian Shield and Adjoining Regions: Insights for Incidents of Great Earthquakes in the Nepal-Bihar-Sikkim Himalaya

The Eastern Indian Shield (EIS) is comprised of the intracratonic (coal-bearing) Damodar Gondwana basin, rift-controlled extensional Lower Gangetic basin (LGB), and downward flexed Indo-Gangetic (IGB). present study involves computations mapping basement configuration, sediment thickness, Moho depth, residual isostatic gravity anomaly, based on 2-D modeling. thickness in area ranges between 0.0 6.5 km, Conrad discontinuity occurs at ∼17.0–20 km depth. depth varies 36.0 41.5 with maximum value beneath Upper (UGB), minimum ∼36 (uplifted Moho) southeastern part LGB. anomaly +44 mGal southern indicates Singhbhum shear zone, LGB, Rajmahal trap to be under-compensated, whereas northern recording –87.0 over-compensated. Although region experienced a few moderate-magnitude earthquakes past, small-magnitude are sparsely distributed. reactivation was possibly associated events magnitudes more than 4.0. Toward south, Bay Bengal (BOB), seismic activities moderate size shallow origin confined aseismic 85 90°E ridges. regions extreme north south [along Himalaya equatorial Ocean (EIO)] moderate-to-great over different times historical but intervening EIS BOB have stability. We propose that two ridges guiding lithospheric stress fields, which being further focused by EIS, BOB, N-S extended regional fault systems into bending zone penetrating lithosphere Himalaya. obliquity plate transecting Foothills channelize enhance field zone. enhanced generates great Nepal-Bihar-Sikkim Himalaya, reflected back through apparently stable creates deformation EIO.