oa Numerical Studies on Relationship between Coda-Q and Stress Field, and Prospects for Application to Real Data

Coda-Q is a stochastic parameter which reflects heterogeneity under the ground. In the past, it is said that the coda-Q has a certain relationship with the occurrence of earthquakes or with the change in a stress field. From the perspective that the coda-Q has quantitative relationship with the stress field, this study attempts to reveal that relationship using the numerical calculations. A 2-D Finite Difference Method (FDM) and a 2-D Boundary Integral Equation Method (BIEM) are employed to consider the effects of the loaded stress in the crust for two kinds of possible causes. One would be the occurrence of anisotropy in the velocity field, and the other the distribution of crack orientations. The former could be dealt with in FDM, while the other with BIEM. The results suggested that the variation in the coda-Q has the relationship with the magnitude of the confining pressure and the angle of principal stress. It is also suggested that both the magnitude of the variation in the coda-Q against the confining pressure and against the angle of principal stress shows higher values when the velocity anisotropy is considered. These results imply the possibility to obtain the change in the stress parameters, i.e., both the magnitude and the orientation, using the variation in the coda-Q. Our further work will be conducted to apply the present methodology and to confirm the stability of coda-Q estimation to real data.