Earthquakes Induced by Rapid Loading of Faults During Pulichintala Reservoir Impoundment in the Stable Continental Region of India

The first stage impoundment of the Pulichintala reservoir in the Proterozoic Cuddapah basin in the southeastern Indian shield began in August 2014. The second stage of impoundment started in 2019 when the height of the dam was increased and the filling of the reservoir was rapid. Soon after earthquakes started occurring which continued for a few months with a maximum magnitude of ML 4.6 on 25 January 2020. Two distinct clusters within the shallow crust were identified, which follow the faults/shear zones in the region. The estimated focal mechanisms with predominant strike slip motion on steep planes and the derived stress state are consistent with the regional stress and plate motion of the Indian plate. We simulated the influence of reservoir impoundment on the inferred seismogenic faults and found that the stress and pore pressure due to reservoir load indeed promoted failure, thus inducing earthquakes. We ascribe the induced earthquakes to rapid filling, longer and higher retention of high‐water levels during 2019–2020, which caused a stress change of 4–8 kPa. This stress change was at least two orders of magnitude higher than the typical tectonic loading rate in the stable continental region of the Indian Shield. Plain Language Summary In this article we documented an unequivocal case of reservoir induced seismicity due to the impoundment of Pulichintala reservoir in the southern Indian Shield. We acquired the earthquake data through a local seismological network and estimated earthquake parameters and focal mechanisms. A short lived small magnitude earthquake sequence initiated immediately after the second stage of impoundment in 2019 when the height of the dam was increased and the filling of the reservoir was rapid. We simulated the influence of reservoir impoundment on the inferred seismogenic faults, which confirms that the causative faults were indeed encouraged for failure due to the reservoir load variations. Rapid loading, longer retention and higher levels of water in the reservoir after second stage of impoundment in 2019 led to a change in stress rate which was about two orders of magnitude higher than the tectonic loading rate in the stable Indian plate region. Quantitative estimation of these features of reservoir filling attests to the previous deductions of incidence of reservoir induced seismicity based on empirical analysis. They also imply that the occurrence of such earthquakes may be avoided by carefully manipulating reservoir loa