【作者】 吕作勇；

【导师】 吴建平；

【作者基本信息】 中国地震局地球物理研究所 ， 地球探测与信息技术， 2009， 硕士

【摘要】 地震层析成像方法是研究地球内部速度结构最有效的手段之一,它能获取地球内部不同深度不同尺度的三维速度图像,为人们深入研究地球内部精细结构提供可靠的信息。华北地区不仅是我国的经济政治中心,也是中国大陆地震活动最为强烈的地区之一,对该地区地下精细结构进行深入研究具有重要意义。为进一步深入研究华北地区地下介质结构,中国地震局地球物理研究所于2006年在华北地区开展了大规模流动地震台阵观测。本文利用华北地震科学台阵和首都圈台网记录的近震和远震P波到时资料,采用近震和远震联合层析成像方法得到了华北地区(111°E-120°E,37°N-42°N)深至700km的高分辨率(水平方向约36km)的地壳上地幔三维P波速度结构,对研究区地壳上地幔横向不均匀性、强震发生的深部构造环境和区内重要的断裂带的深部速度结构特征等进行了研究和讨论。本文研究获得的主要认识如下:(1)华北地区不同构造块体速度结构存在明显差异。华北盆地下方在60-120km深度存在明显低速异常,可能与软流圈有关;在150-350km深度存在明显高速异常,这可能意味着华北盆地岩石圈遭受破坏后仍有古老的克拉通岩石圈残留体存在于上地幔中。渤海盆地下方地幔转换带存在一个较大的低速体,该低速体位于太平洋俯冲板块前缘的西侧,可能与太平洋俯冲板块的相变脱水等有关。山西裂陷盆地一带下方在60-350km存在明显的低速异常,可能与该区上地幔高温低速物质上涌有关。燕山隆起下方60-150km深度表现为连续的高速异常,我们推测是由该地区较大的岩石圈厚度引起的。(2)研究区三维P波速度结构与强震分布对应关系的研究表明多数强震(M≧6.0)往往发生在高、低速异常过渡带上,且震源下方多表现为P波低速异常;强震的发生可能与地壳内存在的流体、壳幔过渡带的不均匀性和上地幔热物质作用等动力学背景密切相关。(3)区内重要的断裂带(太行山山前断裂和张家口-蓬莱断裂带)处在研究区不同块体的交接带上,太行山山前断裂带在地壳中位于高低速异常的分界线附近,至壳幔过渡带这种界线变得很模糊;张家口-蓬莱断裂带在地壳中速度结构较复杂,在60-90km深度位于高低速异常的分界线附近,即位于燕山隆起区较厚的岩石圈块体边缘,表明其深部结构主要受不同块体岩石圈厚度变化的控制。更多还原

【Abstract】 Seismic tomography has become a powerful tool for studying the three-dimensional crust and mantle structure.It can determine the different scales and the different depths of the three-dimensional velocity image,which provides reliable information for people studying the fine structure of the Earth’s interior.North China is our country’s economic and political center,and the earthquake activity of this area is one of the strongest area in China.Therefore,in-depth studying the fine structure of this area has great significance.In order to in-depth study the fine structure of the North China,Institute of Geophysics China Earthquake Administration launched a large-scale movement of seismic array observations in North China in 2006.We determined a high-resolution (horizontal resolution is about 36km) 3D P-wave velocity model of the crust and upper mantle down to the depth of 700km under North China by jointly inverting local events and teleseismic events recorded by North China Seismic Array and Capital Seismic Network.We detailed study the lateral heterogeneity of the crust and upper mantle,the deep tectonic environment of strong earthquake’s occurrence and the deep structure of important fault in North China.The main results are as follows:(1) Different structure blocks in North China have the existence of significant differences in velocity structure.Under North China basin,a pronounced low-velocity anomaly exists at depth of 60-120km,which may relate with shallow depth of asthenosphere,and a pronounced high-velocity anomaly exists at depth of 150-350km,suggesting that old lithosphere residues still exists in the upper mantle through large-scale lithosphere thinning.A large pronounced low-velocity anomaly exists in the mantle transition zone under Bohai sea basin and locates on the west side of the front subducting Pacific slab,which may result from phase transition and dehydration of the subducting Pacific slab.At the depth of 60-350km,a pronounced low-velocity anomaly exists under Shanxi rift basin,which may result form the upwelling of high temperature and low-velocity mantle material under the studying zone.At the depth of 60-150km,a pronounced high-velocity anomaly exists under Yanshan uplift,which may relate with the thick lithosphere. (2)Through studying the relationship between the 3D P-wave velocity structure and strong earthquake distribution,we found that most strong earthquake(M≧6.0) often occurred between high-velocity and low-velocity anomaly transition zone.Low P-wave velocity anomaly exists under the hypocenter.The occurrence of strong earthquakes has the nearly relationship with the existence of fluid in the crust, heterogeneity in the crust-mantle transition zone and the upwelling mantle material.(3)The Taihangshan front fault and the Zhangjiakou-Penglai fault become flimsy tectonic boundaries.The Taihangshan front fault becomes the boundary between high-velocity and low-velocity anomaly in the crust,but the boundary becomes blurred in the crust-mantle transitional zone.The velocity structure of Zhangjiakou-Penglai fault is very complex.At the depth of 60-90km,the Zhangjiakou-Penglai fault also becomes the boundary between high-velocity and low-velocity anomaly,and this fault locates on the edge of the Yanshan uplift which has thick lithosphere,suggesting that the deep structure of this fault may be controlled by listhosphere thickness of the different block.更多还原