Abstract: The seismogenic condition of northwest Yunan Province has been analysed and compared with that of Xianshuihe fault zone:1. Xianshuihe fault zone is a shear zone during the movement of Chuan Dian rhombic block, suffering from greater normal stress σ_n. whlie northwest Yunan is an extensional shear area subjected to smaller normal stress σ_n.2. The joint action of tectonic driving force and the gravitative creeping force caused intensive deformation with higher strain rate along Xianshuihe fault, while the counteraction led up to a medium deformation with lower strain rate in northwest Yunan3. Depth of Xianshuihe fault downs to 15-30 km and paracyclic stick slip events occurred along the brittle preexisting fault. Depth of faults in northwest Ynuan downs to 20 km on the margin and 5-10 km within the area. The events occurred during extension of the area.4. Xianshuihe fault zone is of simple fault geometry, D_f = 1.08-1.2. Northwest Yunan is a complex extensional shear system, D_f = 1.56.5. Physical environment in hypocenter depth of Xianshuihe fault is high confining pressure and medium temperature, while that of northwest Yunan is low confining pressure and medium temperature.

Key words: Seismogenic condition, Extensional structure, Fractal dimension, Shear fault

摘要： 文章在分析滇西北发震构造条件的基础上,把它与鲜水河断裂带进行了对比。滇西北是一个伸展构造区,鲜水河断裂带为一平移剪切带。后者较前者断层面上正应力大、变形强烈、应变速率高。前者断层几何复杂,D_f=1.56,后者断层几何简单,D_f=1.08-1.2。震源深处变形环境前者者为低压中温,后为高压中温。由此造成地震活动性上的差异。

关键词: 发震条件, 伸展构造, 分数维, 剪切断层