Characteristics of reservoir induced stress, pore pressure and their influence on subsurface faults, in terms of fault stability, are calculated to explore the role of TGR in inducing shear failure on the earthquake causative faults. Our analysis suggests that some of the areas of enhanced post-impoundment seismicity can be explained by the shear failure due to the reservoir impoundment. But large regions, not under the unfavourable influence of reservoir induced stress, also exhibit enhanced post-impoundment seismicity. An extremely high pore pressure or some other mechanism, involving fluid interaction with rock mass due to the reservoir impoundment, is required to explain the enhanced seismicity in such regions. We suggest that dissolution and reduced cohesion in the Karst–Carbonate rocks present in the region also assisted in the enhancement of the post-impoundment seismicity. These post-impoundment earthquakes may be termed as fluid-assisted earthquakes in the TGR region rather than earthquakes linked with reservoir induced shear failure. Further, some of the post-impoundment earthquakes of relatively large magnitude which occurred in the region of pre-impoundment seismicity could be purely tectonic in nature and not influenced by the reservoir impoundment.
Figure: Variations of the parameters over the area
Kalpna Gahalaut & Rajesh Rekapalli (2022) Natural Hazards https://doi.org/10.1007/s11069-022-05364-1