Present activity and seismogenic potential of Himalayan sub-parallel thrust faults in Delhi: Inferences from remote sensing, GPR, gravity data and seismicity

摘要

The National Capital Territory (NCT) of Delhi and its environs have been jolted by earthquakes from a far-field seismic source in the Himalayas. Thus the seismo-tectonic activity in this region can be related to thrust faults sub-parallel to the Himalayan thrusts system trending NW-SE. In this present research work various techniques like Remote Sensing (RS), GPR (Ground-Penetrating Radar) and Bouguer gravity anomaly analysis were executed in the Delhi region to identify seismogenic faults sub-parallel to Himalayan thrust systems. The straightening of the Yamuna River and other drainages, separation of the North Delhi ridge from the Central Delhi ridge, shifting of the North Delhi ridge in the north-western direction and linear alignment of vegetation helped in delineating the probable NW-SE faults using satellite image and DEM (Digital Elevation Model) data. These NW-SE faults/thrusts were also identified by GPR (Ground-Penetrating Radar) surveys, using 200 MHz and 100 MHz antennas, carried out at 8 areas. Nearly 200 GPR profiles were taken and the best results were obtained near the Timarpur, Vasant Vihar, Mehrauli and Faridabad areas. The radar profiles were processed using low- and high-pass Finite Impulse Response (FIR) filters, for noise removal and Automatic Gain Control (AGC) for amplitude correction to enhance the data. The Bouguer gravity anomaly analysis confirms the presence of two NW-SE trending faults viz. the Yamuna-Timarpur-Sonepat fault passing from the northern portion and the Faridabad-Mehrauli-Rohtak fault in the southern portion cutting across the city, thus implying the in-between area as a graben. Moreover the fault plane solutions of the majority of the seismic events show orientation in a NW-SE direction along the Delhi Sargodha ridge (DSR). These faults are sub-parallel to Himalayan thrust systems and have reverse fault characteristics. Hence, the possibility of finding more hidden faults beneath the Indo-Gangetic alluvium, sub-parallel to the regional strike of the Himalayan fault system cannot be ruled out.