Influence of pre-existing structural weakness on active tectonics in the eastern part of cratonised Peninsular India: An integrated approach of DInSAR and Numerical Modelling.

Repeated reoccurrence of the low to moderate intensity earthquakes in the Central India region for a long period scruples its acceptability as a stable continental region. In last five years, the National Centre for Seismology INDIA has reported a 27 number of earthquakes of low to moderate intensity around the Tan Shear Zone (TSZ) and Balrampur Fault geofracture in the eastern part of the Central India Tectonic Zone. Moreover, the presence of steep geothermal gradient recorded in the area, only along the aforementioned lineaments, maybe considered as an indirect evidence of frictional heat generation due to seismic/aseismic creep related to tectonic rejuvenation. The kinematics of this reactivation of preexisting structural heterogeneity under the present tectonic configuration is not well understood in this area. The present study has been conducted to address this issue of tectonic reactivation in the area specifically confined between Tan Shear Zone in the north and Balrampur Fault in the south. The Differential Interferometric Synthetic Aperture Radar (DInSAR) technique has been adopted to understand the kinematic of ground movement due to a very recent earthquake event (dated 24 March 2023 with intensity of 3.9) in this zone of interest.   Furthermore, a few numerical experiments have been carried out using finite element method (FEM)  to model the possible influence of preexisting heterogeneity on strain localization in response to current tectonic setup around the study area. In numerical model, we have assumed a hypothetical graben, formed by gravity sag in granitic rheology, filled with layer of sedimentary rheology, equivalent to Gondwana rocks.

Through the DInSAR analysis of SLC image pairs, it has been revealed that the central part spanning ~25 Km length exhibits nearly uniform rate of upliftment due to the earthquake event. The axis of uplift flanked by an undisturbed zone Toward TSZ in the south and the Balrampur Fault in the north, shows a trend parallel to the boundary of Son-Mahanadi graben. For a plausible explanation of the uplift paralleling the preexisting steep graben boundary several hypothetical set-ups were tried with FEM as explained above. Thereby, it has been enumerated that even though the geometric reactivation of the steep graben boundary fault in the reverse-slip mode was not possible, due to stress-buttressing with the preexisting mechanical heterogeneity a hanging wall-cut reverse fault nucleated from the graben collar. Uplift due to this reverse fault resemblance the axial uplift in the study area by its position and orientation with respect to the preexisting structural heterogeneity. This study with multidisciplinary approaches can be considered as a classic example of shallow brittle failure causing seismicity in any Stable Continental Region.