太行山与燕山交汇部位的地壳厚度与泊松比分布特征

Distribution of the crustal thickness and Poisson′s ratio beneath the junction of the Taihangshan and the Yanshan tectonic belts

本文搜集了2001—2013年间在太行山与燕山构造带交汇部位先后布设的4个宽频带流动地震台阵和首都圈固定地震台网共192个台站记录到的全球5.5级以上远震事件波形资料,综合采用接收函数H-κ和CCP叠加分析获得了134个基岩台站下方的地壳厚度和泊松比结果.综合分析与前人研究相吻合但更加精细的地壳约束分布信息,发现研究区域的地壳厚度和泊松比在整体上呈现出从西北到东南方向渐变的特征,在南北重力梯度带两侧及其附近呈现出明显的小尺度地壳结构和物质组分的差异,且可明显区分出太行山地区和燕山构造带及盆山交界处的地壳厚度与泊松比的相对差异,这可能反映了这些地区在华北克拉通的构造演化过程中所经历的不同地壳改造过程.

The information related to the formation and evolution of the North China Craton recorded in its crustal structure has great importance to the study of the North China Craton′s destruction.In recent years,the receiver function method has been widely used to study of crust and upper mantle structure,to obtain more accurate crustal thickness and Poisson′s ratio of the North China area.However,due to the sparseness of permanent seismic stations and the limited distribution of portable seismic stations around the Taihangshan and Yanshan tectonic belts,the published results are not good enough to constraint the tectonic evolution of the junction between the Taihangshan and Yanshan tectonic belts.We used the receiver functions of H-κand CCP stacking methods to determine the crustal thickness and average Poisson′s ratio beneath seismic stations.To overcome the possible problem in station sensor orientation,we visually examined the two horizontal components to estimate the north component azimuth of each station.Then we rotated the two horizontal components of the3-component seismograms into the radial and transverse components.The receiver functions were derived by deconvolution of the radial component of ground motion from the vertical component,which segregates the PS phases.We collect waveforms of worldwide teleseismic events with magnitudes greater than 5.5recorded by 192 seismic stations from the Beijing Digital Seismic Network（BDTSN）and 4temporary broadband seismic arrays deployed in the junction of the Taihangshan and the Yanshan tectonic belts during different periods of 2001—2013.Using the receiver functions of H-κand CCP stacking methods,we calculated the crustal thickness and average Poisson′s ratio beneath134 stations constructed on bedrocks.The comparison of our results of the H-κand CCP stacking methods shows that our results are self-consistent and in conformity with the previous studies,which means reliable.Comprehensively analyzing the fine crustal constraints distribution information in this study leads to the following conclusions.（1）The crustal thickness of the study area gradually decreases from northwest to southeast overall;there is a distinct small-scale differentiation on both sides of the north-south gravity gradient lineament（NSGL）and adjacent regions.（2）The spatial distribution of average Poisson′s ratio in this region is quite nonuniform.There is significant difference on both sides of the NSGL,which indicates the crustal material compositions have obvious regional difference.（3）Strong earthquakes are closely related to the spatial differentiation of the Poisson′s ratio and the difference of crustal medium properties and middle-upper crustal structure.（4）The crustal thickness and Poisson′s ratio can be divided into 2relatively aggregated groups.Though they decrease linearly with the increase of crustal thickness slowly,they may reflect that those areas experienced distinct processes of crustal modification in the tectonic evolution process of the North China Craton.