利用双平面波干涉面波层析成像方法研究山西断陷盆地及鄂尔多斯地台三维速度结构

3D Velocity Structure in Shanxi Graben and Ordos from Two Plane Waves Method

本文利用了北京大学在山西地堑的34个台站以及中国地震局台网中心在鄂尔多斯地区46个台站的远震波形数据,运用双平面波干涉的面波层析成像方法,提取瑞利面波相速度频散曲线,开展台阵覆盖区三维速度结构反演,据此分析了研究区地壳和上地幔的结构特征。结果表明,瑞利面波相速度分区特征显著,山西断陷盆地和渭河断陷盆地的相速度整体偏低。鄂尔多斯块体在莫霍面以下有明显高速异常,表明该地块为构造稳定的克拉通块体,鄂尔多斯块体的岩石圈下界面在120～140km的深度左右。与此相反,山西断陷盆地和渭河断陷盆地地下70～120km左右均有低速异常,显示这两个地区构造活动活跃,这也与该区域历史上多次发生强震是相符的。

Using the broad-band seismic data of Peking University and CENC,taking the method of two plane waves tomography,we have obtain the phase velocities of Rayleigh wave and the 3D shear velocities in Ordos region.Through analyzing the results,we have found the phase velocities of Rayleigh wave in Shanxi graben and Weihe graben are lower.High velocity anomaly beneath moho has been observed in Ordos block,indicate that Ordos block is a stable craton,and its effect extend to 120km depth at least;in the depth between 70 and 120km of Shanxi graben and Weihe graben,shear velocities were lower than origin model,indicating that the substance there had plasticity and these region are strong activity,which is consistent with the activity of earthquake.