郯庐断裂带中南段地壳介质散射强度

本研究运用远震扰动场方法,利用134个数字地震观测台记录的10次远震记录对郯庐断裂带中南段地壳介质散射强度进行研究.结果表明,研究区上、下地壳介质散射强度呈现强烈的横向非均匀性特征,上、下地壳介质散射强度空间分布特征基本一致,散射强度高值区主要分布在华北断块区及秦岭—大别褶皱系的东部地区,散射强度低值区主要分布在下扬子断块区,散射强度峰值区主要分布在六安、莒南、嘉山、烟台等地.地壳介质散射强度与构造块体具有较强的相关性,构造块体不同,地壳介质散射强度则存在一定的差异;沿郯庐断裂带地壳介质散射强度呈现分段性特征,可分为潍坊至临沂段、临沂至嘉山段以及嘉山至九江段三段;地震活动与地壳介质散射强度有较强的相关性,地震多发生在地壳介质散射强度梯度带上,郯庐断裂带的潍坊至临沂段、嘉山至九江段地壳介质散射强度梯度较大,此段中小地震活动较强,而临沂至嘉山段地壳介质散射强度梯度小,中小地震活动相对较弱.地壳介质散射强度与构造块体、断裂构造及地震活动之间的相关性,除反映了深部介质物性可能存在差异外,也可能与深部介质物理形态、物质运移以及深部应力应变环境的变化有关.

The crust seismic scattering strength below the middle-south segment of Tancheng-Lujiang fault zone

The broadband teleseismic waveform data from ten earthquakes recorded by 134 digital seismic stations were selected to study the seismic scattering strength of crust in the middle-southern segment of Tancheng-Lujiang fault zone by the teleseismic fluctuation wavefield method (TFWM). The results show that there exists strong transverse inhomogeneity beneath the middle-southern segment of the Tancheng-Lujiang fault zone, and the spatial distribution of seismic scattering strength exhibits conformity between the upper and the lower crust. The strong seismic scattering strength is found beneath the eastern part of the north China block and the Qinling-Dabie fold system, and the weak seismic scattering strength is found under the Yangtze block. The peak values of seismic scattering strength are mainly distributed in Lu'an, Junan, Jiashan, Yantai et al. The tectonic blocks are correlated with the seismic scattering strength. The different blocks show different seismic scattering strength. The seismic scattering strength, which can be divided into three segments, shows a segmental feature along the Tancheng-Lujiang fault zone. The first segment is from Weifang to Linyi, the second segment is from Linyi to Jiashan, and the last is from Jiashan to Jiujiang. Earthquake activity has a strong correlation with seismic scattering strength, and the epicenters of moderate earthquakes are located along the gradient zone of seismic scattering strength. Many smaller earthquakes occurred along the high gradients of seismic scattering strength along the Tancheng-Lujiang fault zone, such as the segment of Linyi to Jiashan, and the segment of Jiashan to Jiujiang. However, the segment of Linyi to Jiashan with fewer earthquakes shows a low gradient of seismic scattering strength. Seismic scattering strength shows coherency with tectonic blocks, deep fault structure and earthquake activity. It shows that the seismic scattering strength reflects different physical properties of medium in the crust and also is related with the physical morphology of medium, substances migration, and the variation of stress-strain environment in the deep structure.