Estimation of regional stress by FEM for a heterogeneous rock mass with a large fault

Matsuki, Koji*; Nakama, Shigeo ; Sato, Toshinori  

This paper consists of two parts. In Part I, we propose a method for determining regional stress from limited stress data by using a 3D finite element method (FEM) in which we define regional stress for a heterogeneous rock mass composed of different rock bodies and a large fault as a displacement boundary condition that is consistent with the mean trend of in situ stress. This method was applied to a small-scale heterogeneous model with a large planar fault that penetrates the region to clarify the estimation accuracy and the effects of incorrect stiffness of the fault, incomplete stress data, and the assumption that the fault shows partial, but not complete, sliding. The results showed that (1) the method proposed in this study can accurately estimate the stress distribution in the region under consideration except at the bottom when the sliding area of the fault is small, (2) the reproducibility of the given stress indicates that the method can be used to estimate appropriate values of the normal and shear stiffnesses of the fault, and (3) both incomplete stress data and the assumption that the fault does not slide decrease the accuracy of stress estimation while the given stresses are approximately reproduced. In Part II, this method is applied to the Tono area, in Japan.