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

Abstract

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.

Seismic microzoning of the Delhi metropolitan area, India—II: Hazard computation and zoning maps

“…The Pre-Cambrian rocks exposed in the region are the Alwar series of the Delhi Super group. 22,35 The rock formations exposed within and to the immediate south of the NCT comprise metamorphic rocks such as phyllite, slate, quartzite, and schist, whereas the major rock formations to the further south comprise igneous rocks such as pegmatite, granite, and granite gneiss. These rocks occur in the NNE-SSW trending narrow range of low lying hills, ridges and plateaus, which are probably the remnants of a major folded structure.…”

Seismic microzoning of the Delhi metropolitan area, India— I: Seismicity modeling

“…The Punjab and Rajasthan Shelves to the west of the DAFB are parts of the Indus Basin and separated by the NW‐SE trending Sargodha‐Lahore and Lahore‐Delhi Ridges when combined, and known as the Delhi‐Sargodha Ridge (DSR). The DSR is an important regional tectonic feature representing an eroded fore bulge at the periphery of the Himalayan foreland basin that is covered with recent sediment 59,60 . The Rajasthan Shelf to the south of the DSR represents the eastern flank of the Indus basin and comprises the sedimentary tract to the west and northwest of the Aravallis.…”

A holistic seismotectonic model of Delhi region

“…Dubey et al 28 inferred three NW–SE trending reverse faults in the Delhi region using Remote Sensing, Ground-Penetrating Radar (GPR), and Bouguer gravity anomaly data. However, due to very limited depth of penetration of GPR survey (a few meters), modern geophysical surveys with a higher depth of penetration (e.g., Magnetotellurics / Seismic) are imminent to verify and precise characterization of these faults.…”

“…However, due to very limited depth of penetration of GPR survey (a few meters), modern geophysical surveys with a higher depth of penetration (e.g., Magnetotellurics / Seismic) are imminent to verify and precise characterization of these faults. Dubey et al 28 have also suggested that earthquakes that occurred near Rohtak and have orientation other than MDF (i.e. NE-SW) might be related to lithospheric crustal loading of the Himalaya orogeny on the Delhi-Sargoda Ridge.…”