辽宁及邻区背景噪声面波群速度结构研究

收集辽宁及邻区59个宽频带地震仪记录的自2012年1月1日至12月31日的背景噪声连续波形垂向记录, 以背景噪声的方法获取辽宁及邻区面波群速度图像。 过程采用互相关的方法提取瑞利面波格林函数, 利用CPS330提取了群速度的频散曲线, 共从1655条频散曲线中筛选出了1233条信噪比较高的频散曲线。 将研究区划分为0.5°×0.5°的网格, 应用的层析成像方法得到了周期为8~40 s的瑞利面波群速度结构分布。 结果表明: 辽宁地区地壳及上地幔存在明显的横向不均匀性。 短周期群速度分布与研究区内断裂带及地质构造地貌形态表现出良好的相关性, 其中8~15 s周期内群速度分布特征与盆地坳陷、 山区隆起对应性较好, 呈“两垒高, 一堑低”的群速度分布特点, 基本与地质构造相吻合, 地震多位于高低速过渡带内。 较长周期20~30 s的群速度在渤海湾-辽东湾中存在低速异常, 显示了渤海湾盆地和下辽河盆地具有较厚的沉积层覆盖。 35~40 s与莫霍面的深度有明显关联性,莫霍面埋深大体呈西厚东薄的特点。 38~40 s周期内郯庐断裂带东侧的低速异常可能说明渤海内存在局部的热物质上涌现象。 本文结果较好地反映了研究区内地貌地质构造情况, 与区域内地壳及上地幔结构的相关研究成果相吻合, 为辽宁及邻区的地震活动构造背景及地震孕育机理提供重要参考资料。

Surface Wave Group Velocity Structure of Liaoning and its Adjacent Areas based on Ambient Noise Tomography

In this paper, by collecting continuous background noise waveform vertical data recording of 59 broadband seismic stations in Liaoning and its adjacent areas from January 2012 to December 2012,we got the surface wave group velocity images through ambient noise tomography in the study area. We calculated the inter-station Green fuction and extracted the Rayleigh wave group velocity dispersion curves using CPS330. According to quality control and screening, we picked high SNR 1233 group velocity dispersion curves of Rayleigh wave from 1655 dispersion curves, then the study area was divided into a grid of 0.5°×0.5° degree grid by adopting Ditmar &Yanovskaya method and obtained the Raileigh wave group velocity maps at periods 8~40 s in our study. The results show that crust and upper mantle structures of Liaoning region present obvious lateral inhomogeneity. Group velocity distribution at short period is quite well in agreement with known geological and tectonic features in this study area. At the 8~15 s period, the group velocity distribution characteristics have good correspondence with basin and mountain uplift, the characteristic of velocity distribution is the “two horst higher, one graben lower”, and the result mainly coincides with the geological structure. The lower group velocity abnormal appears in the Bohai Bay and Liaodong Bay at periods 20~30 s. This phenomenon mainly reflect that it have existed a thick sedimentary layer in the Bohai Bay Basin and Liaohe basin. For the group velocity maps at longer periods 35~40 s, which are related to the depth of Moho, the distribution characteristics of the depth is that the western is thicker than eastern in the study region. The results illustrate the geological structure and physiognomic characteristics, and also have identical views with correlational studies. In the meanwhile, it also will supply us important useful references to the tectonic background of seismic activity and seismogenic mechanism in Liaoning and its adjacent areas.