Recent Tectonic Stress Field in Northwest Yunnan Province

Based on the collected focal mechanism solutions of M ≥3.0 earthquakes in Northwest Yunnan from 2000 to 2018, we used Michael’s linear inversion method to perform stress tensor inversion, and attempted to analyze the temporal and spatial evolution characteristics of the tectonic stress field in Northwest Yunnan. The results show that the types of focal mechanism solutions of earthquakes in Northwest Yunnan are complex, mainly strike-slip faulting earthquakes (46%), followed by normal faulting earthquakes (27%). The direction of maximum principal stress in the study area is NNW near NS direction, and the direction of minimum principal stress is ENE direction. It shows that the study area is subjected to horizontal compression from NNW near NS direction. According to the variation of the stress tensor variance over time, M≥5.0 earthquakes in the study area mainly occurred when the stress tensor variance was lower than 0.2. Most earthquakes occur when the variance of the stress tensor decreases, that is, when the focal mechanism solutions tend to be consistent. And these earthquakes mostly occur in the low value area of the variance and its edge.