面波偏振与中国大陆岩石层横向不均匀性

SURFACE WAVE WAVE POLARIZATIONS AND LATERAL HETEROGENEITIES OF THE LITHOSPHERE IN CHINA

本文利用７个ＣＤＳＮ台站的长周期数字地震记录和奇异值分解方法，分析了在中国大陆内传播的基阶勒夫波的偏振方向，从而确定波到达台站时的入射方向对于大圆方向的偏离．５°—１０°的偏角是常见的，最大偏角可达２０°左右．尤其是４０ｓ以下的勒夫波，在大多数路径上都显著偏离．这些观测到的现象可以用勒夫波穿过不同大地构造单元界线发生的折射作出定性解释．青藏块体的边界和天山褶皱带可引起２０—６０ｓ（或更长）周期的勒夫波发生折射；华北与华南地块间及华北平原和鄂尔多斯地块间的速度差异一般影响２０—４０ｓ之间的勒夫波；扬子地台与东南沿海褶皱的差异主要影响２０ｓ以下的波；２０ｓ以下的短周期勒夫波往往表现出复杂的多重路径现象．

The polarizations of fundamental-mode Love waves propagating in the Chinesecontinent were analysed with the single value decomposition method using digitallong-period seismic data recorded by 7 CDSN stations.The deviations of wave approach direction from the great-circle path at these stations and their relations withthe wave period were thus determined. An angle of deviation between 5°and 10°is Sommonly seen along many paths, and the maximum is near 20°.For Love waves below 40s period, significant deviation from the great-circle direction is foundalong the majority of paths studied. These observed phenomena canbe reasonablyexplained by wave refractions at the boundaries between different tectonic blocks.The boundaries of the Qinghai-Tibet block and Tianshan fold belt cause refractionsof Love waves of 20 to 60s(or longer) period. The velocity difference between theNorth and South China blocks,as well as between the North China Plain and Ordos Plateau, affects mainly the Love waves in the 20 40s range. The differencebetween the Yangtze platform and the southeast coastal fold belt affects waves below 20s.Short period Love waves below 20s often show multipathing.