Constraining temporal changes in seismic velocity at the Xinfengjiang Reservoir using ambient seismic noise interferometry

Abstract

Changes in seismic velocity at the water reservoir are crucial for understanding the underground media environment and monitoring seismic activity. Notably, Xinfengjiang Reservoir (XFJR) is one of the four reservoirs worldwide known to have induced earthquakes exceeding magnitude 6.0, raising great concerns on its seismic triggering environment. However, there has been a notable lack of research on monitoring the stress variations that contribute to seismic activity. Here, we applied ambient seismic noise interferometry to study relative changes in seismic velocity (dv/v) in the XFJR using data recorded from permanent seismic stations between 2013 and 2021. We identified significant seasonal variations in the dv/v and discussed these changes with seismic activity, ocean tidal response, reservoir water level, and underground water level. Our findings indicate that changes in the reservoir water level play a significant role in the seasonal variations of dv/v, with a strong positive correlation to the reservoir water level gradient, and an anti-correlation to the underground water level gradient, corresponding to the loading and pore pressure effects, respectively. This study demonstrates that ambient seismic noise is an effective tool for monitoring changes in the underground medium of water reservoirs.