In 1967, a powerful earthquake measuring 6.3 on the Richter scale struck beneath the Koyna Dam in Maharashtra, India, according to the United States Geological Survey (USGS). This quake is considered the largest known induced earthquake, meaning it was caused by human activity rather than natural tectonic forces. The Koyna Dam, a massive concrete structure 103 meters high, was built to generate hydroelectric power. Its reservoir, named Shivajisagar, can hold 2.8 billion cubic meters of water—roughly the equivalent of 1.1 million Olympic swimming pools. Before the dam was constructed, the area was considered geologically stable, with no history of earthquakes. The earthquake was triggered by the weight of the water in the reservoir, which seeped into the surrounding rock and altered the existing stresses in the Earth's crust. These changes in pressure, estimated to be between 0.75 and 2.25 bar—similar to the pressure in a car tire—were enough to activate a pre-existing fault line. Studies suggest that the region beneath the dam contains strike-slip faults and a "pull-apart" basin hidden under layers of basalt rock. While such pressure changes are tiny on a global scale, they can be significant for faults that are already under stress, leading to a sudden release of energy in the form of an earthquake. Since the dam began filling in 1962, seismic activity in the area has followed the pattern of water levels in the reservoir. Annual fluctuations, influenced by the monsoon season, have kept the earthquakes active for decades. Scientists have identified three key factors that contribute to these quakes: the rate at which the reservoir fills, the water level rising above previous peaks, and how long the high level is maintained. Over the past 50 years, the Koyna area has experienced about 20 earthquakes of magnitude 5 or higher, 400 of magnitude 3.5 or higher, and thousands of smaller tremors—far more than expected for such a region. The situation was further complicated by the nearby Warna reservoir, located 15 kilometers south of the Koyna Dam. Starting in 1987, its filling added to the stress on the fault system, increasing seismic activity. The regularity of the quakes has made Koyna a unique and important site for scientific research. A drilling project aimed to study the fault zone where the 1967 earthquake occurred, reaching depths of about 6 kilometers. Researchers hope to better understand how water pressure can trigger such events. While the reservoir itself is not the ultimate cause of the earthquakes, it acts as a catalyst. Koyna is not an isolated case—similar incidents have been recorded elsewhere, such as a magnitude 6.1 earthquake near the Hsinfengkiang Dam in China in 1962, just two years after the dam began holding water.