CHARACTERISTICS OF CURRENT CRUSTAL DEFORMATION OF ACTIVE BLOCKS IN THE SICHUAN-YUNNAN REGION
QIAO Xue-Jun WANG Qi DU Rui-LinGPS Laboratory, Institute of Seismology, China Earthquake Administration, Wuhan 430071,China Institute of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China
The Sichuan-Yunnan area are divided into nine active secondary crustal blocks based on several GPS repeat surveys at more than 200 GPS sites during 1998～2002. The Euler rotation vectors of nine secondary blocks, the velocities of main faults and strain field of the area are calculated and analyzed. The results indicate that the crustal movement of the area in north and west are stronger than that of south and east. The Sichuan-Yunnan rhombic block is characterized by clockwise rotation. The velocities of those blocks outside the rhombic block decrease swiftly. Different rates derived from GPS and geology data show that the current crustal motions become stronger from north to south within the rhombic block. The eastward extrusion of the Qinghai-Xizang plateau presents a marked drop in the middle-Yunnan block and the absorption effect of the Lijiang-Xiaojinhe fault is invisible. The Sichuan-Yunan area is dominated by compressive strain. The strain concentration at Shimian of Sichuan province and Xinping of Yunnan province implies a possible moderate or major seismic risk.