Rapid Seismicity Monitoring After the March 2023 Ms 4.5 Earthquake Around the Xinfengjiang Reservoir, China

Abstract Reservoirs that have experienced induced earthquakes provide ideal inland settings to understand earthquake reactions to fluid loading and migration. The Xinfengjiang Reservoir, one of only four reservoirs documented with ML>6.0 events after impoundment in the 1960s, has proven to be a critical site for studying reservoir-induced seismicity. On 8 March 2023, an Ms 4.5 earthquake struck the Wudong area in the northwestern sector of the Xinfengjiang Reservoir, a corner previously overlooked because of the rarity of felt-level events. In response, we immediately deployed 29 three-component nodal seismometers to monitor the subsequent seismic sequence following this Ms 4.5 mainshock. Adopting a state-of-the-art machine learning–based seismic detection and location workflow, we constructed a high-precision catalog of 2081 events (−0.8<ML<2.8, Mc=−0.4) within 21 days. All events are located with hypocenter uncertainties of <90 m, forming into two earthquake clusters—the Wudong and the Xichang seismic clusters—separated by an ∼3 km gap. The Wudong cluster clearly delineated a northwest–southeast-oriented fault (striking at 155° and dipping at 87°) that hosted ∼52.5% of our detections. As for the Xichang cluster, evidence of fluid migration from the reservoir bottom to ∼10 km depth is supported by the spatiotemporal seismicity pattern and potential non-double-couple components. Using the recently deployed nodal array, our study provides a comprehensive source analysis of the recent Ms 4.5 cluster, promoting further understanding of seismogenic processes beneath the Xinfengjiang Reservoir.