Abstract: The P-wave first motion solutions are given in this paper for 70 shocks of magnitude equal to and greater than 4 which occurred in Southwestern China and adjacent areas during 1973—1979. The relative motion of intraplate blocks including the Yun-nan-Xikang rhombic block,Sichuan-Qinghai block,and the Southwestern Yunnan block is studied on the basis of the focal mechanism,seismic fissures,horizontal deformation in the seismic areas and the trend of variations of the length of baselines across major faults.The direction of the lateral motion of crustal material of three blocks in question is SE-SSE.The Yunnan-Xikang rhombic block can be devided into several sub-blocks and their relative motion is also discussed in this paper.

摘要： 本文给出中国西南及邻区1973—1979年70个M≥4级地震的P波初动解。用震源机制、地震裂缝、震区水平形变及跨主干断层基线长度复测的长趋势变化,讨论了以康滇菱形断块为中心、北及川青断块、南和滇西南块断带的板内断块相对运动。上述三块体的地壳物质移动方向为南东—南南东。同时,探讨了康滇菱形断块内部的相对运动。