张家口-渤海地震活动带及其邻区的地壳厚度与泊松比分布

Crustal thickness and Poisson's ratio beneath Zhangjiakou-Bohai seismic active belt and its neighboring regions

利用山东、河北、辽宁、北京、天津等区域地震台网记录的远震资料,采用接收函数H-k叠加搜索方法,得到了张家口—渤海地震活动带及其邻区99个台站下方的地壳厚度和平均泊松比估计.研究结果显示:研究区地壳厚度在30—46km之间显著变化,地壳厚度与地表地形相关性很好,呈现出从隆起区到盆地区逐渐减薄的变化趋势;研究区地壳泊松比具有明显的分区特点,燕山地区泊松比偏低可能与该地区克拉通破坏方式以拆沉为主有关,郯城—庐江断裂带山东段出现的泊松比高低混杂现象可能与该地区火山活动有关,张家口—渤海地震活动带西段与隆起的交汇地带,部分台站下方地壳的泊松比值偏高,可能是断裂带附近岩石比较破碎与岩石部分熔融共同作用的结果.此外,位于渤海湾中间岛链上的北隍城台下方地壳较厚,泊松比较低,其原因尚待查明.

Based on the teleseismic events recorded by seismic stations of Shan-dong,Hebei,Liaoning,Beijing,Tianjin regional seismograph networks,this paper investigates the crustal thickness and average Poisson’s ratios beneath the stations by means of H-k receiver function stacking method.The results show that the crustal thickness in the studied region varies from 30 km to 46 km,and is thinning gradually from mountain to basin,suggesting a good correlation with surface terrain.On the other hand,distribution of the Poisson’s ratio overthe studied region is characterized by an obvious region segmentation.The low Poisson’s ratios beneath the east part of Yanshan might relate to the delaminationof North China craton.The region beneath east part of Tancheng-Luj iangfault zone exhibits a complex distribution of low Poisson’s ratios mixed withhigh ones,which might be related to volcanic activity.The convergence zone ofthe western segment of Zhangj iakou-Bohai seismic active belt and the lift exhibitsa little higher Poisson’s ratios,which might be caused by both broken rocksand the partial fusion of rocks near the seismic active belt. The station Beihuangcheng located on the island chain in the Bohai Sea shows a thick crustalthickness and a low Poisson’s ratio,but the reason behind the phenomenonwaits for further investigation.