华北地区Lg尾波衰减研究——Lg尾波Q的测量

A STUDY OF Lg CODA ATTENUATION IN NORTH CHINA——THE MEASUREMENT OF Lg CODA Q

利用 1989～ 1998年间发生在中国华北地区ML≥ 3.0级的地震事件 ,华北遥测台网以及数字化台网记录到的信噪比较高的Lg尾波时间序列 ,经过滤波、消除背景噪声等预处理 ,采用单台记录叠加频谱比法 ,得到传播路径上Lg尾波Q0 (Q =Q0 fη ,Q0 是 1Hz的Q值 ,η是Q值与频率相关系数 ) ,进而获得该地区Q0 和 η的空间分布 .测量结果表明 ,华北地区地壳Lg尾波Q0 值分布存在显著的横向不均匀性 ,这种不均匀性与该地区地壳的速度分布基本一致 ,表现为与该地区地表地质特征明显的一致性 ,即传播路径位于太行山隆起和燕山隆起区为高Q0 值分布 ;传播路径位于冀中坳陷和黄骅坳陷等平原区表现为低Q0 值 ;传播路径位于隆起区和坳陷区二者之间 ,其Q0 值也介于二者之间 ,说明华北地区的地壳结构没有很大的阶跃式变化而使波导遭到破坏 ,Lg尾波Q0 值基本上反映了地壳内介质滞弹性的固有衰减 .

By using Lg coda time series with higher signal-to-noise ratio from North China telemetry and digital seismic network during the period from 1989 to 1998 (M L≥3.0), the spatial distribution of Lg coda Q (Q Q 0 fη ) is obtained with the stacked spectral ratio method through pretreatments of filtering and eliminating background noise. The results show that there is a significant lateral heterogeneity on Lg coda Q distribution in North China, which is approximately consistent with the velocity distribution in the crust of the region, and is related with the surface geological features. There are higher Q 0 values on propagating paths located in upwelling areas, and lower Q 0 values in depression areas. There are eclectic Q 0 values on propagating paths located in both upwelling and depression areas. On one hand the crustal structure in North China region there is no great step change so as to destroy seismic wave-guide. On the other hand Lg coda Q 0 value reflects basically intrinsic attenuation of the crustal medium anelasticity.