Numerical and Analytical Studies on Increasing Near‐Fault Fracture Stiffness to Control Induced Seismicity Based on an Equivalent Continuum Modelling Approach

ABSTRACT The frequency and magnitude of induced seismicity have been increasing in recent times. Induced seismicity can cause significant damage to underground workings and therefore has become a major global issue. Hence, it is necessary to assess and mitigate the associated risks of induced seismicity. Previously, various methods have been implemented to minimise the hazards of induced seismicity to underground workings. However, their effectiveness is limited due to the inherent heterogeneity of the stress state within natural geological structures. This can result in unexpectedly large seismic events in distant regions away from anthropogenic activities, such as ore extraction and fluid injection/production. Hence, the present study aims to develop a novel method to control the intensity of induced seismicity by increasing the stiffness of the fault damage zone surrounding the fault core. In the present study, the effect of increasing fracture stiffness in the damage zone on seismic source parameters is investigated. First, the validity of the proposed method is assessed through an analytical study by evaluating energy released from a seismic event whilst assuming linear slip‐weakening behaviour. Then, a mine‐wide numerical model is constructed that can reproduce a complex and heterogeneous stress state within the fault damage zone by computing and applying equivalent compliance tensors to each element in the model, based on a discrete fracture network composed of millions of fractures. A parametric study is subsequently carried out to quantitatively analyse the effect of fracture stiffnesses under distinct fault zone cases: (a) different near‐fault fracture densities, (b) different fracture dips, (c) different dip directions, (d) different depths, (e) different distances from fault core and (f) different initial stiffnesses. The results indicate that fracture stiffness significantly affects all the seismic source parameters in most cases. When the fracture stiffness is increased by a factor of five, the seismic source parameters are decreased to approximately 40%–50%. This result was found to closely align with that derived from the analytical study. However, its effectiveness becomes less significant with decreasing fracture densities, with seismic source parameters reduced only to 50%–75%, compared to approximately 40% under higher‐density conditions. Furthermore, the seismic source parameters remain almost unchanged with increasing distance from the fault core. These results suggest that increasing fracture stiffness within a severely fractured rock mass in the vicinity of the fault core can effectively mitigate seismic hazards. This work may provide a foundation for future implementation of increasing fracture stiffness as a means of reducing seismic risk.