Numerical Modeling of Complex Stress State in a Fault Damage Zone and Its Implication on Near‐Fault Seismic Activity

Abstract

AbstractNear‐fault severe seismic activity is frequently observed when excavating deep underground during various engineering projects. The present study elaborates a method to simulate the heterogeneous, complex stress state inside fractured rock mass in a fault damage zone, based on the concept of equivalent elastic compliance tensor and boundary traction method. After verifying the method with the discrete element method, the stress state of the fault damage zone composed of millions of fractures was analyzed. It is then demonstrated that the method is capable of simulating stress anomalies that could be the cause for severe seismic activity. The quantitative analysis indicates that the discrepancy between local and regional fracture densities is one of the dominant factors that produce an intensely stressed region, suggesting the use of local‐to‐regional fracture density ratio as an index to evaluate the potential for stress anomalies and its degree. Furthermore, a model parametric study on fracture properties was carried out to provide insight into the discrepancy in the likelihood of abnormal stress state between jointed host rock and fault damage zone. Lastly, b‐value was computed from thousands of possible seismic events identified in the model, by assuming seismic efficiency and scaled energy. The computed b‐value was found to fall within a reasonable range estimated from induced seismicity in deep underground mines. These results imply that the proposed method may be used to obtain a first‐order approximation of the complex rock mass stress state in fault damage zones and to evaluate the severity of seismic activity.