資源開発技術／開発機械／岩盤工学

[3K0101-10-10] Relation between the depth of an induced seismic event and the coefficient of kinetic friction, considering seismic efficiency

○Sainoki Atsushi¹, Chiaki Hirohama¹ (1. Kumamoto university)

司会：才ノ木 敦士（熊本大学）、羽柴 公博（東京大学）

Keywords:induced seismicity, slip-weakening distance, seismic efficiency, deep underground mine

Due to the depletion of shallow ore deposits, mining depths have been increasing around the world, posing the risk of induced seismicity. Although the numerical simulation of induced seismicity has been intensively performed to estimate its risk, an accurate estimation of seismic source parameters has not yet been achieved. This is mainly attributed to the difficulty in estimating the mechanical properties of the causative fault. Specifically, it is quite challenging to determine the critical slip-weakening distance D_c and the coefficient of kinetic friction µ_d, which directly pertain to the dynamic slip-weakening behaviour during fault-slip, thus influencing the magnitude and intensity of the simulated seismic event. The present study addresses this issue by considering seismic efficiency η. Seismic efficiency is defined as the ratio of seismically radiated energy to total potential energy change during seismic event and is known to be less than 0.06, irrespective of event magnitudes. In this study, induced seismicity was simulated with a slip-dependent constitutive law, using a 3D numerical model whilst varying the depth of the source location. It was found from the analysis results that η steadily increases with the increasing depth when D_c and µ_d are kept constant. This indicates that the assumption that D_c and µ_d are independent of the depth is incorrect, i.e. either of the parameters should vary depending on the in-situ stress state. In light of this result, further numerical analyses were performed whilst calibrating µ_d and D_c for each depth so that the condition of η ≈ 0.06 is maintained. The result was then compared to laboratory experiments conducted in previous studies, giving an insight into how the properties of the fault varies with the depth. The obtained knowledge contributes to placing a constraint on the mechanical properties of faults when performing the numerical simulation of induced seismicity.