青藏高原东南缘及邻区地壳介质散射强度变化特征

基于远震扰动场方法,利用47个数字地震观测台记录的10次远震记录对青藏高原东南缘及邻区地壳介质散射强度进行了研究.结果表明研究区内地壳介质横向非均匀性强烈,扬子块体地壳介质散射强度与青藏块体存在较为明显的差异;地壳介质散射强度梯度带与主要断裂带分布趋势一致,龙门山断裂带、安宁河断裂带与地壳介质散射强度梯度带具有较强的相关性,散射强度高值区偏向青藏块体一侧;强震震中沿散射强度梯度带分布,其震中偏向散射强度高值区一侧;散射强度呈现纵向非均匀性特征,下地壳介质散射强度高于上地壳.研究区强、弱散射强度的空间分布可能与区内强烈的地质构造运动、频繁的地震及火山活动所引起深部物质破碎、熔融及其沿断裂带的上涌与运移有关.

Variations of the crust seismic scattering strength below the southeastern margin of the Tibetan plateau and adjacent regions

The ten broadband teleseismic waveform data recorded by forty-seven digital seismic networks were selected to study the seismic scattering strength of crust in the southeastern margin of the Tibetan plateau and adjacent regions by the teleseismic fluctuation wavefield method (TFWM). The results show that there exists strong transverse inhomogeneity beneath the southeastern Tibetan plateau and adjacent regions. The scattering strength of the Yangtsz block and the Tibetan block has obvious difference. The gradient zone of seismic scattering strength is along the main fault zone. The position of the Longmenshan fault and the Anninghe fault have strong correlation with the gradient zone of seismic scattering strength. In addition, the high value region of strong seismic scattering strength is almost turning to the Tibet side. The epicenters of strong earthquakes are along the gradient zone of seismic scattering strength, and lie the side of strong scattering strength. The scattering strength shows the characteristic of vertical inhomogeneity and the scattering of lower crust is stronger than the upper crust. The spacial distribution of the strong and the weak scattering strengths maybe related to the strong movement of geological tectonics, the broken medium caused by frequent tectonic and volcanic activity, and also with the heat flow upwelling along active faults.