Juxtaposition of Shallow Reservoir-Triggered Seismicity and Deep Tectonic Locking in the Qiaojia-Dongchuan Seismic Gap

2026-07-21

AI Summary

This study addresses the challenge of identifying the critical state of mature seismic gaps, where anthropogenic perturbations such as reservoir impoundment often obscure the silent accumulation of tectonic strain. Leveraging a high-resolution earthquake catalog from a dense seismic array in the Qiaojia–Dongchuan region, combined with spatial b-value analysis, Coulomb stress accumulation rate calculations, and imaging of complex-dip fault structures, the research reveals a vertical decoupling mechanism between shallow, fluid-driven induced seismicity (characterized by high b-values ≈1.0) and deep-seated locked asperities at depths of ~20 km (exhibiting low b-values <0.8). This finding proposes a novel model in which shallow induced activity is mechanically decoupled from deep tectonic locking, offering critical criteria and a new framework for seismic hazard assessment in reservoir–fault systems.

Abstract

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.

Problem

• seismic gap
• reservoir-triggered seismicity
• tectonic locking
• stress accumulation
• earthquake risk assessment

Innovation

• reservoir-triggered seismicity
• tectonic locking
• b-value
• stress accumulation
• seismic gap