Study On The Characteristics Of Current Tectonic Stress Field In Yunnan Based On Focal Mechanism Solution Inversion

The meaning of Tectonic Stress Field is:A combination of stress which acts on the crust (or lithosphere), and related on a certain tectonic unit with its development. In another word:The sum of the stress magnitudes and directions in the crust (or lithosphere) which caused by tectonic movement in a certain moment. It is the cause of crustal movement and deformation, also an important part of earth dynamics. Tectonic Stress Field are used widely, It’meaningful in tectonic theory, earthquake analysis and prediction, constructions projection of seismic hazard for its research.Inversion of Tectonic Stress Field based on Focal Mechanism data is one method in many researches. It’s belonging to geophysics. The advantages of the method are:1, It has clear physical meaning based on tectonic, rock mechanics and solid mechanics;2, Results include the information of deep or seismic fracture part. It’s beneficial for understand and grasp the deep stress state;3, Research on data acquisition is low cost;4, the outputs of results are fast;5, On the condition of security data results is reliable.In the research, the reliable focal mechanism data of the year between1999and2004and the magnitude greater than3(between3and6.6) which have been deleted after-quake in Yunnan region are collected. There are590seismic events used to inversion calculation and statistical analysis. According to previous research results, divide Yunnan region into39parts on1°×1°square.It’s comprised27data sets. Then we did the inversion. Comparison of statistics and inversion methods and combined the results of Xiaofeng Cui indicate that source control in Yunnan area had no significant change; Because the push of the Burma block of Yunnan and the activities of structural belt of Longmen mountain in Sichuan, the tectonic stress field in Baoshan and Zhaotong are obviously changed; Both the method of statistic dominant direction of P axis and inversion method are highly sensitive to the number of seismic events. When the numbers of earthquake are small, the difference of two is discrete, showed the characteristics of nonlinear; when the earthquake is greater than the number of30, different is convergence, and tends to be more linear. Consistency of the two also from a side reaction reliable results. Therefore, the seismic number is essential for studying regional tectonic stress field in geophysical methods.