华北地区Lg尾波衰减研究——Lg尾波Q_0地震成像

A STUDY OF LG CODA ATTENUATION BENEATH NORTH CHINA: SEISMIC IMAGING OF LG CODA Q_0

利用单台记录叠加频谱比法测量出的华北地区 5 6 0余条单台传播路径上平均Lg尾波Q0 值数据 (Q0 是1Hz的Q值 ) ,采用随机褶积模型和奇异值分解法 ,重建该地区地壳中Q0 的横向变化 .结果表明 ,华北地区地壳中Lg尾波Q0 值分布具有显著的横向不均匀性 ,这种不均匀性与地质构造明显相关 ,块隆区具有较高的Q0 值 ,例如 ,燕山造山带、太行山块隆、鲁西隆起 ;华北平原区表现为低Q0 值分布 ,例如冀中坳陷、黄骅坳陷、济阳坳陷 ,二者界限分明 .结合研究区内的大地热值分布研究表明 ,低Q0 值区大都处于高热流区 ,这可能是地壳内热物质的活动有关 .虽然华北地区Lg尾波Q0 值高、低分区明显 ,但是 ,从总体上应该属于低Q0 值异常区 ,也就是说 ,该区的地壳是高地震波衰减区 ,这可能是该地区受太平洋板块和欧亚板块的相互作用而使地壳减薄 。

By using 560 Lg coda Q 0 values measured on propagating paths, the Q 0 image in the crust beneath the North China region is restructured with a stochastic modeling and the singular value decomposition. The result indicates that there is remarkable lateral heterogeneity on Lg coda Q 0 distribution in the crust beneath the North China region, similar to the velocity image, and closely related with the known surface geological features: the low Q 0 areas exist beneath the Taihang and Yanshan mountains and the Luxi uplift area, and high Q 0 values appear below the Jizhong, Huanghua and Jiyang depressions and the plain areas. There is a clear division between the high and low Q 0 values. Compared with the heat flow values in North China, most the low Q 0 value areas are located in the high heat flow areas. It is possibly related with hot material activity in the crust below these areas. Although there is a clear difference between the high and low Q 0 value areas in the crust of North China, as a whole the North China belongs in low Q 0 value abnormal region. It means that the region is a high seismic wave attenuation area. Probably it is resulted from the interaction between Eurasia and Pacific plates, which causes the crust thinning and hot material upwelling.