Surface Signatures of Basement Fault Reactivation in the Ganga Plain

The Ganga plain is a vast foreland basin between the Himalaya on the North and the peninsular region in its South. The thick alluvial cover of the plain overlies the basement which encompasses several basement ridges and transverse faults. These basement ridges and faults have great influence on the Ganga plain tectonics. The geomorphic evidence suggests tectonic control on the surface drainage as the River Ramganga shows a 4-5 kms southward shift in its channel in the south of Moradabad Basement Fault. The Moradabad basement fault (MBF) beneath the Ganga plain strikes transverse to the Himalayan trend. The present study shows several field evidences of surface deformation caused by the basement fault reactivation. Soft sediment deformation structures (seismites) and surface faults found at four different locations on the trace of the Moradabad Basement fault in the Upper Ganga plain. Ground penetrating radar (GPR) survey across the fault also provides evidence of shallow subsurface deformations. The epicenters of historical earthquakes are concentrated along the Moradabad basement fault zone. The deformations can be attributed to possible pre-historic earthquake event associated with MBF because other impulsive stresses like slope instability, flood surges and rapid sediment deposition are absent. Close association of these secondary faults and deformation structures with the Moradabad basement fault indicate their origin is due to the stress release along this fault created by Himalayan tectonics.