Long-Time Delays in Induced Earthquakes Caused by Low-Permeability Bodies: Insights From the Xinfengjiang Reservoir, China

Abstract

In many cases of induced seismicity, earthquakes occur significantly delayed to the initiation of industrial activities, yet the mechanisms behind these long-time delays remain poorly understood. In the Xinfengjiang Reservoir, an earthquake swarm became active in 2010, nearly 50 years after the initial impoundment in 1959. In this study, we conducted high-resolution 3D velocity tomography and focal mechanism analysis using a dense local seismic network. High-resolution seismic imaging identifies two downward migration channels enabling fluids to infiltrate the bedrock and low Vp/Vs anomalies at 5–10 km corresponding to low-permeability granitic bodies. Numerical simulations indicate that these Vp/Vs anomalies can delay pore-pressure diffusion by decades, resulting in delayed triggering of seismic events in the northwest of the reservoir. Our findings highlight the critical influence of low-permeability bodies in controlling the spatial-temporal evolution of reservoir-induced earthquakes and underscore the need to reconsider long-term seismic risk assessments for reservoirs situated in similar geological settings.