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This study investigates the interplay between shallow reservoir-triggered seismicity and deep tectonic locking in the Qiaojia-Dongchuan seismic gap, utilizing a high-resolution dense array catalog. The researchers found that while shallow seismic activities are characterized by high b-values indicative of fluid influence, deeper seismicity reveals a locked state with low b-values and significant stress accumulation, suggesting a critical seismic risk. This vertical decoupling mechanism highlights how induced seismicity can obscure the underlying tectonic strain, offering a novel framework for global seismic risk assessment in reservoir-fault systems.
Shallow seismic activities can obscure the critical accumulation of deep tectonic strain, revealing a hidden risk in reservoir-fault systems.
Identifying the critical state of mature seismic gaps is challenging, especially when anthropogenic stress perturbations, such as reservoir impoundment, superimpose on tectonic loading. Here, utilizing a high-resolution dense array catalog from the Qiaojia-Dongchuan seismic gap (hosting the second-largest hydropower station in the world), we reveal a distinct vertical decoupling mechanism. The shallow activities exhibit high b-values (1.0), indicative of fluid-driven reservoir-triggered seismicity. Conversely, deep seismicity (20 km) outlines a'locked asperity'characterized by low b-values (less than 0.8) and high Coulomb stress accumulation rate. We further identify a complex dipping structure, suggesting compound fault kinematics. Additionally, the calculated stress accumulation suggests this seismic gap is in a critical state with elevated rupture potential. Our findings indicate that shallow induced seismicity can mask the silent accumulation of deep tectonic strain. This decoupling model provides a new framework for assessing seismic risks in reservoir-fault systems globally.
