摘要
通过搜集首都圈地震台网记录到的634个地震事件的近三万条地震射线,并从中挑选出274条信噪比高、发育良好的面波频散曲线,并将已有的纵波速度转换为横波速度,作为横波速度反演的初始模型,利用最小二乘反演方法进行面波频散层析成像,得到了研究区地壳S波速度结构和地壳的厚度分布以及一些初步结论:地壳可分为地表、基底、上地壳、中地壳、下地壳五层,中地壳整体横波速度表现为弱梯度,局部出现负速度梯度,下地壳横波速度均呈现不同程度的异常,证实了中地壳低速层的存在;研究区内速度存在明显横向不均匀性,这是复杂的地质构造特征在地球物理场中的响应;各构造单元表现明显不同的速度结构变化,中地壳层位速度变化范围较小;同一构造单元在不同深度的层位上速度变化明显,出现高低速异常交替现象,特别是在张渤断裂带上地壳层位以上,高速和低速异常块体交替明显;地壳平均厚度29～40km,并且从东南向西北逐渐变厚加深,其中张北地区地壳最厚达40km,华北裂陷盆地地壳厚度为29～32km,华北裂陷盆地中部的深浅交叉的异常块体内的冀中坳陷构造最薄。
We picked up 274 well-developed and high signal to noise performance surface wave ray-paths recorded by 38 seismic stations in the Capital Seismic station Network and study the crust of the Capital region by surface wave tomography method through the original velocity model from P velocity transformation.Then we obtain,analyze and interpret the depth section and S wave velocity structure.Here are some preliminary results： firstly,the area crust could be divided into five layers： surface,basement,upper crust,mid-crust and lower crust.The mid-crust S velocity structure shows low gradient,even negative velocity gradient partly,and S velocity shows different degree anomaly in lower crust.So this further proved the truth of mid-crust exist.Secondly,S wave velocity profile shows obvious lateral heterogeneity in the Capital region,for this is the response of the complex geological structural characteristic in the geophysical field;Every tectonic unit shows obvious different velocity structures,and the velocity changes less in mid-crust layer;the same tectonic unit has clear different velocity changes in different depth,and the high velocity and low velocity alternate abnormally,particularly,above the crust layer of the fault zone.Because of Zhangjiakou-bohai sea rift broken belt,higher velocity and low velocity abnormal block alternate obviously.thirdly,the crust average thickness in the Capital region is from 29 to 40 kilometers,and presents the distinguishing feature that the thickness more thicker and deeper from southeast to northwest,the most thick area is Zhangbei area around Zhangjiakou,in the North China rift depression basin,the crust thickness is from 29 to 32 kilometers,and the most thin place is located in North China basin.
出处
《工程地球物理学报》
2012年第2期175-183,共9页
Chinese Journal of Engineering Geophysics
基金
国家自然科学基金(编号:40804017和40974077及41164004)
国家科技专项项目(编号:SinoProbe-02-02-02)联合资助
关键词
首都圈
面波反演
S波速度结构
Chinese capital region
surface-wave inversion
S wave velocity structure
