Abstract: In this paper, Sichuan-Yunnan and its adjacent areas are divided into Yajiang, Central Yunnan, Sichuan-Qinghai, Central Sichuan, and Myitkyina-West Yunnan blocks. The mode and rates of motion of these blocks and their boundaries are studied separately. The predominant direction of the principal compressive stress axes within the blocks is analyzed in term of focal mechanism solutions of 442 moderate strong earthquakes. The models of focal faulting are determined through the rake angles λ obtained from source parameters of 771 events with magnitudes about 3 or more, and they are evidenced by focal faulting or slip modes derived from the distributions of N axis plunges of P-wave first motion solutions for moderate-strong earthquakes. A comparison is made between the moment tensor rates for moderate-strong earthquake and the calculated annual average slip rates of each seismotectonic zones within the blocks. Based on regular resurveying of across fault short level lines and baselines during the period of 1980-2001 along the border of the Sichuan-Qinghai, Yajiang and Central Yunnan blocks, the annual average rates of horizontal and vertical deformation for each site are analyzed. The motion rates of the Sichuan-Yunnan Block are inhomogeneous. The Sichuan-Qinghai Block moves toward SEE direction, and the predominant direction of the principal compressive stress axis falls in the range of N100°～130°E. The motion rate of this block is smaller than that of the Yajiang block, implying a delayed motion relative to that of the later. As a result, the Xianshuihe Fault between these two blocks displays a strong left lateral displacement. In addition to earthquakes of strike-slip type, the earthquakes of reverse dip-slip type are also predominant in the Sichuan-Qinghai Block. The predominant direction of the principal compressive stress axes in the Yajiang Block is within the range of N160°～170°E, i.e. SSE. The motion rate of this block is larger than that of the Sichuan-Qinghai Block, and the percentage of strike-slip type earthquakes in this block is larger then that in the other blocks. The motion direction of the Central Yunnan Block is nearly the same as that of the Yajiang Block, leaning slightly to the east. The predominant direction of the principal compressive stress axes in this block is in the range of N150°～160°E, and there are various types of earthquake failure including strike-slip, normal dip-slip, and reverse dip-slip. The direction of the principal compressive stress axes in the Central Sichuan Block falls in the range of N110°～140°E, approximately the same as the motion direction of the South China Block. The percentage of strike-slip type events in this block is relatively low, and there is a portion of events belonging to normal dip-slip or oblique dip-slip types. The motion rates at the northeast boundary between the Yajiang and Central Yunnan Blocks are greater than those at the west and south boundaries. The SSE-directed motion of the blocks is associated with right lateral component. Similarly, as the motion rates of the eastern boundary of the Sichuan-Qinghai Block is greater than that of the Longmenshan belt to the southeast of the block, the SSE-directed motion of the Sichuan-Qinghai Block is also associated with right lateral component. Two predominant directions of the principal compressive stress axes in the Myitkyina-West Yunnan Block indicate the NE-directed squeezing and the SE-directed escaping of the block, while the motion rate of the block is larger than that of the Yajiang and Central Yunnan Blocks. This might be attributed to the dynamic mechanism of the formation of collision and squeezing belts due to the direct action of the Asam Wedge while Indian Plate moving northward.

Key words: Sichuan-Yunnan Block, focal mechanism, block motion, motion rate

摘要： 用442次中强地震的震源机制解分析了川滇次级地块应力场的优势方向.使用771次3级左右地震的滑动角λ参数统计确定震源断层的错动方式,并用中强地震P波初动解的N轴仰角的统计分布结果得到的震源断层错动或滑动型式去佐证.拟合中强地震的矩张量速率式,计算了川滇次级地块各地震构造区的年均滑动速率,并进行比较.根据1980-2001年川青地块、雅江地块和滇中地块边界断裂带跨断层短水准、短基线定期复测结果,分析了水平和垂向年均形变速率.川滇地块间的运动是不均匀的.川青地块的运动方向为SEE.雅江地块压应力场优势方向为SSE,相对川青地块的运动速率更大.滇中地块承袭雅江地块的运动方向,略偏东.密支那滇西地块压应力场有2组优势方向,存在向NE方向的推挤和SSE方向的逃逸,活动速率大.

关键词: 川滇地块, 震源机制, 地块运动, 运动速率