辽宁及邻区背景噪声相速度结构研究

The study of ambient noise phase velocity in Liaoning and adjacent areas

收集辽宁及其周边地区(吉林、河北、山东、内蒙)70个宽频带地震仪2012年连续背景噪声波形数据,基于地震背景噪声层析成像方法,得到研究区面波群速度及相速度图像。利用台站对互相关方法,提取瑞利面波格林函数,采用时频分析法(FTAN)获取2416条相速度频散曲线,从中筛选1661条信噪比较高的频散曲线。将研究区以0.25°×0.25°进行网格化,采用Ditmar等提出的层析成像反演方法,得到周期10—40 s的瑞利面波群速度及相速度结构分布图。与群速度结果相比,分辨率更高,研究区大部可达0.5°×0.5°(局部可达0.25°×0.25°)。结果表明,辽宁地区地壳及上地幔面波相速度结构存在显著的横向不均匀性。在周期10—15 s的群速度图中,浅层及中上地壳速度分布与研究区地形地貌及主要地质构造单元具有较好的对应关系,盆地及沉积层低速,山区隆起高速,且在高低速转换带多为地震孕震区;在周期20—30 s相速度结构图中,下地壳至上地幔顶部深度范围内,相速度速度结构主要受地壳厚度及渤海湾内巨厚沉积层的影响,在海城至大连区域内出现的低速异常推测为地下热物质上涌;随着深度的增加,在周期30—40 s的相速度图中,速度分布逐渐受控于莫霍面起伏,明显变化出现在辽东半岛,由高速变为低速。

In this paper,by collecting vertical component data of continuous background noise recorded by 70 broadband seismic stations in Liaoning and its adjacent areas(Hebei,Shandong,Inner Mongolia,Jilin)from January 2012 to December 2012,we get the surface wave group velocity images through ambient noise tomography in the study region.We calculated the Green function using the cross-correlation of station pairs and extracted the Rayleigh wave group and phase velocity dispersion curves by the FTAN method.According to quality control and screening,we pick 1661 high SNR phase velocity dispersion curves of Rayleigh wave from 2416 dispersion curves.Then,the study area is divided into grids of 0.25°×0.25°,by adopting the Ditmar&Yanovskaya method,the structure distribution maps of the group and phase velocities of the Rayleigh wave in periods of 10-40 s are obtained.The results show that crustal and upper mantle structures of the Liaoning region present obvious lateral inhomogeneity.Group velocity distribution in the short period is in quite good agreement with known geological and tectonic features in the study area.In the 10-15 s period,the group velocity distribution has a good correspondence with the topography and geological structures,showing two high-velocity regions corresponding to mountain uplifts and a low-velocity region corresponding to a basin.A low phase velocity anomaly appears in the Bohai Bay and Liaodong bay in periods of 20-30 s.This phenomenon indicates that there is a thick sedimentary layer in the Bohai Bay Basin and the Liaohe basin.The low-velocity anomaly in the area from Haicheng to Dalian is supposed to be caused by the upwelling of underground hot material.The phase velocity map in longer periods of 30-40 s is related to the depth of Moho.The depth distribution characteristic is that the western is deeper than the eastern in the study region.