川滇地区断层相互作用的地震活动证据及有限元模拟

对川滇地区主要活动断裂地震活动性的分析表明 ,该区主要活动断裂间存在地震活动的相关性 :1)强震活跃期沿着鲜水河断裂、小江断裂、红河断裂、龙陵 -澜沧断裂及NE向的龙门山 -瑞丽断裂依次迁移 ;2 )鲜水河断裂与龙陵 -澜沧断裂不仅在强震活动上 ,而且在b值变化上存在较强的相关性 ,是平行断裂在区域应力场作用下相互作用的结果 ;3)龙门山 -瑞丽断裂与上述川滇地区其它近NW向断裂间存在地震交替活动的现象 ;4 )龙门山 -瑞丽断裂的地震具有分段活动的特征 ,是断块差异活动的体现。有限元分析显示 ,上述断层相互作用现象是块体非均匀运动过程中应力场调整的反映 ,是块体运动的结果。研究表明川滇地区主要断层地震活动间存在 3种相互作用的现象 ,即块体边界迁移型、旋向相反平行断层交替型和交叉断层交替型

SEISMIC EVIDENCE AND NUMERICAL SIMULATION FOR FAULT INTERACTIONS IN SICHUAN-YUNNAN REGION

In this paper,seismicities along the main active faults in Sichuan-Yunnan region,including the Xian-shuihe,Xiaojiang,Honghe,Longling-Lancang and Longmenshan-Ruili Faults,are analyzed.The results reveal four phenomena of fault interactions:1)the active period of strong earthquake initiates at first on the Xianshuihe Fault,and then initiates in succession on the Xiaojiang,Honghe,Longling-Lancang and Long-menshan-Ruili Faults.The migration of the initiation time of active period of strong earthquake is consistent with the movement state of Sichuan-Yunnan continent characterized by southeastward horizontal slipping as-sociated with clockwise rotation;2)the b value and the activity of strong earthquakes on the Xianshuihe Fault bear a close relation to those on the Longling-Lancang Fault.The two faults are parallel to each other and have opposite sense of slip;3)seismic activity on the NW-trending main faults in this region occurs alternately with that on the NE-trending Longmenshan-Ruili Fault;4)seismicity on the Longmenshan-Ruili Fault is characterized by segmentation,which reflects the differential movement of the fault blocks bounded by various segments of the fault. In addition,finite element method is applied to simulate the variation process of stress field caused by fault interactions in Sichuan-Yunnan region.The results show that the fault interactions mentioned above are closely related to block movement and hence to the adjustment of stress fields.In this paper,three types of fault interactions are recognized through the analysis of seismicity along the main faults in Sichuan-Yunnan region.They include the migration of seismicity along block boundaries,the alternation of seismic-ity on parallel faults with opposite slip sense,and the alternation of seismicity on intersecting faults.