| Summary: | The extreme rainfall weather during the Indian monsoon season has increased in recent decades changing the hydrological mass distribution that may be responsible for triggering regional earthquakes. In the western Himalayas, a shallow Mw 5.7 earthquake took place right after the withdrawal of the 2019 unusual Indian summer monsoon resulting in a rapid increase of ~4.5 km3 of water storage at the nearby Mangla reservoir within three months. Through a joint inversion of space geodetic and teleseismic data, we found that the mainshock occurred on the décollement structure of the Main Himalayan Thrust in the western Himalayas, which was previously underdetermined. The significant water loading, and pore pressure diffusion led to Coulomb stress increases of ~10 kPa on the maximum coseismic slip zone promoting fault failure. Our findings demonstrate that climate change could influence certain reservoir-associated earthquakes in the Himalayas. We provide recommendations to improve the regulations for the reservoir operations in Mangla and probably other contexts with similar tectonic settings in the Himalayas during the monsoon season.
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