No 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.

The metasediments in the Chamba region experienced three phases of deformation: DF 1 , DF 2 and DF 3. Folded quartz veins are co-folded with the F 2 crenulation folds. Their geometric and tectonic significance is studied by microstructures and shortening adjacent to the discrete crenulation cleavage, S 2. Microstructures of folded vein segments, their geometric changes and truncation to cleavage (S 2) are mainly due to pressure-solution phenomena and the estimated volume loss from reconstructed vein segments range from 16 to 25.5%, which is closely related to volume decrease (26%) calculated from the polydeformed slates of North Wales areas.

This paper deciphers the late stress systems involved in the development of kink bands in the perspective of thrust regime. In kink bands, the correlation coefficient for α-β plots is positive near thrusts and negative away from thrusts. The plots show nearly linear relationship near thrusts and non-linear relationship away from thrusts. The rotation was prominent mechanism of kink band formation near thrusts and rotation coupled with shearing, along the kink planes away from thrusts. Along thrusts σ 1 is horizontal E-W trend and it rotates to horizontal N-S trend away from the thrust. The proposed model establishes that (1) the shearing along kink planes led to angular relationship, β < α and (2) the kink planes of conjugate kinks could be used for paleostress analysis even in those cases where shearing along these planes has occurred.

First phase folds F 1 developed in polydeformed Ajabgarh Group rocks of Proterozoic age are studied using various geometrical methods of analysis for compatibility of homogeneous strain in both class 1-3 pairs by correlating t α /α plots with existing curves for competent layers and matching t α /α plots with the flattening curves for the incompetent layers. F 1 folds were initiated by the process of buckling but underwent [(λ 2 /λ 1) = 0.2 to 0.7] for competent layers and R-values of 1.1 to 5 for incompetent layers. The varying flattening is also revealed by the geometry of folds. The apparent buckle shortening of folds which ranges between 49 and 67 per cent with a majority of the folds having shortening values between 50% and 55% (exclusive of layer parallel strain) and inverse thickness method strain up to 50%. Besides flattening, the fold geometry was also modified by the pressure solution. This is borne by the presence of dark seams rich in phyllosilicates and disseminated carbonaceous material offsetting limbs of buckled quartz veins in slates.