Analysis Of The P-velocity Anisotropy Of The Upper Crust In The Northern Xiaojiang Fault

According to a broad literature reading, the seismic anisotropy research status and methods have been studied. What is more, we mainly focus on the seismic anisotropy research progress of the mainland, especially surrounding in the Xiaojiang-Fault zone. On the basis of the study and research, as the particularity of earthquake observation in the northern of Xiaojiang-Fault zone, this paper puts forward the method which the P wave travel time residuals are used to calculate the residual slowness vector researches underground anisotropy, and uses the method named Remaining Slowness Vector Method to apply in the northern of Xiaojiang-Fault zone in Yunnan province of China. Application results show that the residual slowness vector technique is a useful tool to analyze the seismic wave velocity anisotropy, and the p-wave velocity anisotropy of upper crust in the northern of Xiaojiang-Fault zone associated with local long-term stress state.Specifically, as observation velocity field superposition of isotropic and anisotropic in two-dimensional case for the premise, the paper illustrates the principle of using the method of arrival time residual of seismic wave velocity for researching anisotropy and puts forward the concrete calculation process. And finally, it calculate all residual slowness vectors surrounding stations by using the P traveling-time residual values of 6746 events recorded by 24 stations of the Qiaojia Array of the northern of Xiaojiang-Fault zone, and these residual slowness vectors are put together to obtain the directions of the fast P-velocity or slow P-velocity. The results show that the directions of the P velocities at most of the stations are in good agreement, with the fast P velocities pointing to southeast while the slow P velocities to northeast. It is interesting that the direction of the fast P velocities agrees with that of the P axes of local stress field and the direction of the slow P velocities agrees with that of the T axes, implying that long period of stress acting might be one of the important factors of the anisotropy in this region.