Abstract: The middle section of the Xiaojiang fault zone located in Yunnan Province is branched into east and west two faults. Between these faults there are many NE trending smaller faults and blocks cuted by nearly SN and EW trending faults. They make up the network shape structure with rectangular geometry of the middle section of the Xiaojiang fault zone. These NE trending faults inherited those of Tertiay and were innovated in Quartary with left-lateral slip. Some of them have been active till Holocene. Their activities belong to the integrated left-lateral slip motion of the Xiaojiang fault zone with much smaller magnitude and rate comparing with the main faults. Because of their motion the main faults have bending or step areas which are barries for stress and strain concentration. The blocks between the east and west main faults are cut by the NE trending faults into many secondary blocks of diamond and shuttle shape. Relative movements occur between these blocks which have important effect on the segmentation of faults as well as earthquake occurrence.

Key words: Xiaojiang fault, Fault block tectonics, Faulting activity

摘要： 小江断裂带中段东西支断裂间存在的NE向断裂是在第三纪NE向断裂的基础上,于第四纪中晚期开始新的活动,并具有左旋走滑运动的特征,有些在全新世仍有活动。它们的活动从属于小江断裂带的整体左旋走滑运动,其运动幅度和速率比近SN向小江东西支断裂小得多,但是由于它们的运动,使主断裂产生弯曲或阶区,形成有利于应力和应变集中的障碍。夹于东西支断裂之间的断块被NE向断裂切割为多个次级菱形和梭形断块,这些断块之间的相对运动对断裂分段和地震孕育过程具有不可忽视的影响。

关键词: 小江断裂, 断块构造, 断层活动