岩盤工学・採掘技術に関する研究の動向と新たな展開（Recent trend and advancement in mining and rock engineering）

[2301-06-02] Fundamental Study on Aseismic and Seismic Fault Activities at a Great Depth

○Atsushi Sainoki¹, Chiaki Hirohama¹ (1. Kumamoto University)

司会：奈良禎太（京都大学）
Chairman: Yoshitaka Nara (Kyoto University)

キーワード：Fault seismicity , Numerical analysis, Aseismic fault movement, Underground mine, Induced seismicity

The seismic activity of faults at a great depth plays a pivotal role in various engineering projects such as underground mines, geothermal reservoirs, CO₂ sequestration sites, and oil and gas production sites. Although numerical analysis techniques have been developed to simulate the behaviour of such a fault, an emphasis is predominantly placed on estimating its shear movement without considering how fast the fault slips and how much energy is dynamically released as seismic waves. The quasi-static shear movement of a fault does not cause severe damage, while violent, intense slip releases a large amount of seismic energy that reaches to the ground surface and induces ground vibration. Thus, it is of importance to gain a better understanding of geological, geotechnical, and in-situ stress conditions that dictate aseismic and seismic fault behaviour.
This study is based on a conceptual model extending several hundred meters and including a major fault subjected to overburden pressure and horizontal stresses. Using the model, fault-slip is artificially induced by quasi-statically changing the stress state of the fault, i.e. decreasing its normal stress and/or increasing its shear stress, assuming stress change caused by mining activity, fluid pressure change, and/or rock temperature change. When fault-slip takes place, the quasi-static condition is changed to dynamic, whereby fault-slip rate is examined until the slip ceases. On the basis of the simulation method, various influential factors are investigated such as the influence of geotechnical properties, fault stiffness, kinematic frictional coefficient fluctuation, and the properties of the surrounding rockmass on the dynamic behaviour of the fault. This study aims to lay a foundation for the accurate estimation of fault seismic activity caused by the development of underground.