中国大陆Rayleigh面波衰减特征研究

搜集中国大陆58个数字地震台站6312个长周期波形记录,从中挑选出符合条件的442对经过中国大陆的双台路径记录,采用相匹配滤波和频率域维纳滤波相结合的方法,计算出双台之间的混合路径衰减系数。对中国大陆进行网格划分,通过网格化反演得到中国大陆每个网格单元的纯路径衰减系数。结果显示:短周期Rayleigh面波总体表现为东部(中国东北、华北、华南)Rayleigh面波衰减小,西北部(以青藏高原为中心)Rayleigh面波衰减大,反映了该深度东部地区已进入上地幔,西部仍处于下地壳;Rayleigh面波在中周期衰减特征是呈SN向展布,将中国大陆分成以鄂尔多斯—四川盆地为中部的三分图像,衰减小的中西部岩石圈稳定区、衰减大的青藏高原岩石圈汇聚增厚区和东部岩石圈拉张减薄区;在长周期Rayleigh面波衰减特征是中国大陆中西部衰减较小,为印度大陆俯冲到该深度所致,而在东部衰减较大,为西太平洋边缘弧后盆地的地幔浅部上升热流,构成上地幔中的热室而使东部面波衰减较大。Rayleigh面波衰减与地壳上地幔温度关系显示:中国大陆Rayleigh波衰减与大地热流分布有一定相关性——研究区域内热流值较高的青藏地块及邻区表现为Rayleigh波衰减大,热流值较低的中国东部表现为Rayleigh波整体衰减小;中国大陆地震波衰减特性与强震分布关系密切,在大约以107°E为界的中国大陆西部地震明显强于中国东部,与此关系密切的是,在约107°E为界大陆西部(以青藏高原为中心)地震波衰减大,以东的大陆地区衰减明显减小。

The attenuation of Rayleigh surface wave in China's mainland

442 pairs of Rayleigh wave were selected from 6312 wavefoms recorded by 58 stations in China’s mainland.The attenuation coefficients of the Rayleigh wave in China were obtained by using the phase-matched method and the frequency-domain Wiener filter.The authors made inversion of the attenuation coefficients of the Rayleigh wave in China’s mainland with grids 4o×4o,and obtained the distribution of attenuation coefficients in different periods in China’s mainland.Some conclusions have been reached:i) the attenuation of Rayleigh wave is lower in eastern China than in northwestern China in a short period,which shows that this depth is the upper mantle in eastern China and the crust in western China;ii) the formation of the attenuation of Rayleigh wave is in SN-direction,which divides China’s mainland into three parts: the middle part is from Ordos to Sichuan,characterized by stableness and low attenuation,whereas the other two parts are of high attenuation in the middle period;iii) the attenuation of Rayleigh wave is higher in eastern China than in northwestern China in a long period,probably due to the subduction of Gondwana land to this depth in northwestern China and the upwelling of the back-arc basin in West Pacific Ocean to this depth;iv) the relationship between the attenuation of Rayleigh wave and heat flow is that the regions such as Qinghai-Tibet block and its adjacent areas whose heat flow is high are of high attenuation,and the regions such as eastern China and its adjacent areas whose heat flow is low are of low attenuation;v) the relationship between the attenuation of Rayleigh wave and strong earthquake is intimate,as shown by the facts that more strong earthquakes and high attenuation of Rayleigh wave occur west of 107°E and less strong earthquakes and low attenuation of Rayleigh wave occur east of 107°E.