Effect of fracture stiffness in a fault damage zone on seismic source parameters of induced fault-slip

Abstract

It is well recognized that inherent stress concentration within a fault damage zone may lead to induced fault-slip, resulting in severe damage to underground facilities. Previous research suggests that the intensity of fault-slip is influenced not only by the mechanical properties of the fault core but also by the stiffness of the surrounding rock mass, implying that fracture stiffness could be an important factor that needs to be studied. Therefore, in this study, the effect of the fracture stiffness on seismic source parameters of induced fault-slip is investigated using a mine-wide scale heterogeneous continuum model. The model is constructed based on a discrete fracture network within a fault damage zone, utilizing the crack tensor theory and boundary traction method. The fault core is simulated as a discontinuous plane with interface elements at the center of the model, and fault-slip is induced by gradually reducing the effective normal stress on the fault plane. Seismic source parameters are computed and analyzed under various fracture stiffness conditions. Seismically radiated energy is defined as the work done by the stress perturbation across a closed surface at a distance from the earthquake source, while seismic moment is calculated using the moment tensor of a seismic source in an anisotropic medium. This study investigates increasing fracture stiffness while maintaining a normal-to-shear stiffness ratio of three. Dynamic analysis results reveal a notable impact of fracture stiffness on seismically radiated energy and seismic moment, both of which decrease significantly with increasing fracture stiffness. These findings imply the importance of considering fracture stiffness for more accurate estimation of seismically radiated energy and seismic moment.