北京西北地区壳幔结构的非均匀性特征与地震活动

利用在北京西北部地区穿过张家口——渤海地震带北西段地震测深剖面进行了综合解释和研究， 揭示了延庆——怀来、 张北——尚义地震活动区异常的深浅地壳结构特征. 结果表明： 研究区基底结构具有明显的起伏变化， 不同的地质构造单元基底埋深存在着较大差异. 基底埋深在局部地段呈现出的急剧变化可视其为基底断裂存在的一种标志， 基底断裂与地壳深断裂的存在为岩浆的上溢提供了条件， 从而导致了地壳结构强烈的非均匀性. 延怀地区壳内复杂反射波组序列和局部强弱不连续反射带现象的出现， 表明该地区地壳结构发生了强烈的挤压变形， 从而构成了该地区复杂的地壳结构， 为该地区地震的发生提供了动力来源； 张北——尚义地区壳内不同深度范围低速异常体和局部的C1界面的存在， 可以认为是岩浆多期活动的产物， 在区域构造活动的作用下脆性的上地壳内， 当局部应力积聚到一定的程度从而引发了地震的发生.

THE HETEROGENEOUS CHARACTERISTICS OF CRUST MANTLE STRUCTURES AND THE SEISMIC ACTIVI TIES IN THE NORTHWEST BEIJING REGION

In this paper, the abnormal characteristics of the crustal structures in the seismic active region, Yanqing Huailai and Zhangbei Shangyi, are obtained by means of comprehensively interpreting and studying the data of deep seismic sounding profiles passing through the northwestern part of Zhangjiakou Bohai seismic zone. The results show that the fluctuation of crystalline basement in the study region is obvious and that there exist considerable differences in depth in different geological units. The locally abrupt variation of crystalline basement depths may be regarded as a mark of existence of crystalline basement faults. These crystalline basement faults and deep crustal faults provide a pass for the magma to rise, resulting in the strong inhomogeneity of crustal structures. These phenomena of the complex seismic reflected waves and locally discontinuous reflection zones with different energy indicate that the intensive squeeze and deformation of crust took place, which have led to the complex crustal structures and offered the dynamic source for the earthquake occurrence in this region. The low velocity bodies in different depths of crust and locally interface C 1 in Zhangbei Shangyi region may result from repeated magmatic activities. The certain stress accumulation in the brittle upper crust can cause the occurrence of earthquake under the action of local tectonic activity.