【作者】 刘建华； 刘福田； 阎晓蔚； 何建坤；

【Author】 Liu Jianhua Liu Futian Yan Xiaowei He Jiankun (Institute of Geophysics,Chinese Academy of Sciences)

【机构】 中国科学院地球物理研究所；

【摘要】 本文利用1989～1991年间发生在北京及其邻近地区M_l≥3.0的地震,北京遥测地震台网记录到的信噪比较高的Lg尾波系列,采用单台记录叠加频谱比法,得到传播路径上Lg尾波Q（Q=Q₀f^η,Q₀是在1Hz下的Q值）,进而获得该地区Q₀和η的分布特征。研究结果表明:1)SSR法是测量地壳介质剪切波平均Q的可供选择的好方法之一,它的优点在于由震源谱、记录场地及仪器响应所产生的影响在频谱叠加过程中受到抑制,可保证计算Q₀和η的稳定性。2)北京及其邻近地区地壳内Q₀的分布存在显著的横向不均匀性,同地表已知的地质构造特征明显相关,相比之下,太行山隆起区和燕山隆起区为高Q₀区,其值约为200～300,冀中拗陷及平原区则表现为低Q₀异常,其值约为150-180。Q₀值的这种分布特征与华北地区地壳内地震波速度分布特征基本一致。值得指出的是,虽然北京及其邻近地区地壳平均Q₀值横向分布差异明显,但其值相差并不很大,在150～300之间变化,显著低于典型的大陆地盾区。例如,非洲西部地盾区的Q₀值约为960,加拿大地盾的Q₀值高达1100;与频率依赖关系指数η大约在0.5～0.9之间变化,显著高于大陆地盾区（η≈0.30）。这可能是由于库拉-太平洋板块向中国大陆东部斜向俯冲,使华北地区上地幔物质大规模上涌,形成剧烈的构造岩浆活动及新生代大陆裂谷区,使该地区地壳变"软"变热,从而对地震波产生强烈的吸收,表现为低Q₀值。更多还原

【Abstract】 In this paper by using high signal-to-noise ration Lg coda time series from Beijing telemetry seismic network during the period from 1989to 1991（Ml>3.0）,the spatial distribution of Lg coda Q（Q=Q₀f^η） is obtained with the stacked spectral ratio method（SSR method）.The results are summarized as follows:1.SSR method is one of the choice method for crustal Q measurement,its advantage is that source spectral,local site effect and instrument response can be largely weakened during the spectral stacking process,ensuring the stability of Q₀ andηcalculation.2.There is a significant lateral heterogeneity on Lg coda Q distribution in Beijing and adjacent regions,closely related to the well known geological features of surface,namely,the high Q₀ areas exist in Taihang mountain and Yanshan mountain upwelling areas,and Q₀ value is about between 200and 300;Jizhong depression and the plain areas are of low Q₀,and about 150-180.These features of Lg coda Q₀ distribution are consistent with the velocity distribution in the crust of North China. It is worth to point out that although there is obvious difference of Lg coda Q₀ in North China region,the values are relatively low as whole,and are between 150 and 300.They are lower than that in a typical continental shield area.For example Q₀ value is about 960 in West Africa continental shield area,and 1100 in Canadian continental shield area.ηvalues are 0.5～0.9 in North China,and higher than that in continental shield areas（η≈0.3）.It is possible that the subduction of Kula-Pacific plate beneath East China resulted in mande material upwelling and large-scale rifting.The crust became hot and the seismic wave attenuation became strong.更多还原