DIRECTIONS OF MEAN STRESS AXES IN SOUTHWESTERN CHINA DEDUCED FROM MICROEARTHQUAKE DATA
XU ZHONG-HUAI WANG SU-YUN HUANG YU-RUI GAO A-JIA JIN XIAO-FENGCHANG XIANG-DONG(Institute of Geophysics, State Seismological Bureau, Beijing)
The orientations of the mean principal stress axes in eastern part of Qing-Zang plateau and Yunnan area are deduced from first P-wave polarity readings of microearthquakes, which occurred in this region during the period of 1975 to 1984. The result indicates that, while both P (compressional) and T (tensional) axes are horizontal, their azimuths show a tendency of rather regular rotation from a NE-SW compression in the north, then E-W in the middle part, to a NNW-SSE or nearly N-S compression in the southern part. This pattern of stress axis directions may be attributed to the joint action of the northward push of the India plate to the Qing-Zang plateau and the southwestward pull of the sinking material in the Burma intermediate-depth seismic zone to the Yunnan area.