Top-down and bottom-up fluid diffusion jointly induce seismicity in the Weiyuan shale gas field, China

Shale gas development has been linked to induced seismicity, yet previous studies mainly focus on the role of fracturing fluids and hydraulic fracturing process. Here, we unravel the complex interplay between hydraulic fracturing and earthquake generation in the Weiyuan shale gas field, China, by integrating a high-resolution earthquake catalog with 3D seismic velocity models. Our analysis reveals that 'top-down' diffusion of fracturing fluids and 'bottom-up' ascent of gases, facilitated by pre-existing faults, lead to elevated pore pressure that primarily controls the seismicity. This can explain the events that occur down to ~ 10 km depth and the faster migration of deep events. We further show that fluid infusion triggered aseismic slip or stress accumulation that drives reactivation of basement faults and migration of seismicity. Our findings provide clear evidence that seismicity could be induced by deep bottom-up fluid migration, which is crucial for assessing seismic hazards associated with unconventional resource development.