深地震反射剖面揭示的天津地区张渤带地壳精细结构  

Fine crustal structures of Zhangjiakou-Bohai tectonic zone in Tianjin area revealed by a deep seismic reflection profile

作　　者：闫成国[1] 曹井泉[1] 陈宇坤[1] 刘保金[2] 高武平[1] 姬计法[2] 张文朋[1] 酆少英[2] YAN ChengGuo;CAO JingQuan;CHEN YuKun;LIU BaoJin;GAO WuPing;JI JiFa;ZHANG WenPeng;FENG ShaoYing(Tianjin Earthquake Agency,Tianjin 300201,China;Geophysical Prospecting Center,China Earthquake Administration,Zhengzhou 450002,China)

机构地区：[1]天津市地震局,天津300201 [2]中国地震局地球物理勘探中心,郑州450002

出　　处：《地球物理学报》2020年第12期4431-4439,共9页Chinese Journal of Geophysics

基　　金：天津市科技重大专项“地震风险预警技术及服务产品研发与应用”项目(18ZXAQSF00110);国家自然科学基金(41772123);天津市“十二五”蓟运河断裂探测项目(津发改投资[2016]647号)共同资助.

摘　　要：穿过天津地区张渤带的长86 km、NE向深地震反射剖面揭示了该区清晰的地壳精细结构图像和断裂的深浅构造特征,为研究张渤地震构造带的深部孕震环境和构造模式提供了地震学证据,对探讨晚中生代以来华北裂陷盆地的深部动力学过程及演化具有重要意义.结果表明,天津地区张渤带地壳以结晶基底反射T G为界,分为上下两部分;上地壳反射波组丰富,分层特征明显,界面起伏形态清楚,清晰地刻画出冀中坳陷新生代沉积分层、箕状沉积凹陷的底界、潮白河断裂、蓟运河断裂及丰台—野鸡坨断裂的几何结构;地壳内部结晶基底(T G)至Moho之间,显示出近于“反射透明”的地震波场特征,无明显震相,这与华北其他地区的深地震反射剖面结果明显不同;地壳厚度为30.0~34.5 km,总体变化趋势为中段地壳厚而南北端相对较薄,Moho在横向上显示出明显的不均匀和横向间断特征,在Moho被错断处存在两个明显的反射事件R A和R C,R A可能是软流圈热物质上涌的侧向残留物,叠层状反射震相R C则表现出壳幔过渡带特征;剖面揭示了2条错断Moho的超壳深大断裂(F D1和F D2)和9条上地壳断裂,深大断裂应是软流圈热物质上涌,造成上地幔隆起而形成的,上地壳断裂与地壳垂直运动及侧向引张力有关;超壳深断裂(F D1和F D2)为本区深部热物质的上涌与能量交换提供了通道,而与之对应的地壳浅部断裂(F 3和F 9),则为能量调整提供了可能的条件,断裂邻近区域可能是未来发生强震的地区,值得注意.A NE-trending deep seismic reflection profile with 86 km long across the Zhangjiakou-Bohai tectonic zone in Tianjin area was completed in 2018.This profile reveals the fine crustal structure image and the tectonic features of the faults in this tectonic zone.It provides new seismic evidence for the research on the deep seismogenic environment and tectonic patterns of the Zhangjiakou-Bohai tectonic zone.These results are of great significance for the discussion on the deep dynamic and evolutionary process of the North China rift basin since the Late Mesozoic.According to this study,the crust of the Zhangjiakou-Bohai tectonic zone in Tianjin area is divided into the upper part and the lower part based on the reflection T G of the crystalline basement.The reflection wave groups in the upper part of the crust are abundant and present obvious layers.The clear ups and downs of the interfaces clearly depict the Cenozoic sedimentary layers of the Jizhong depression,the bottom boundary of the“dustpan shaped”sedimentary depression,and also the geometry of the Chaobaihe,Jiyunhe and Fengtai-Yejituo faults.On the contrary,there has no distinct seismic phase in the area between the crystalline basement(T G)and the Moho surface,which has great differences from the results of other parts of North China.The crustal thickness ranges from 30.0 to 34.5 km,and the crust in the middle segment is thicker than both the north and south segments.The Moho surface presents prominent inhomogeneity and discontinuity in the transverse direction,and there are two obvious reflection events,R A and R C,at the area where the Moho surface is offset.The R A may be the lateral residue of the upwelling of the asthenosphere.The laminated reflection seismic phase of R C presents characteristics of the crust-mantle transition zone.This profile reveals 2 deep faults offset the Moho surface(F D1 and F D2)and 9 upper crust faults.The deep faults should be caused by the uplift of the upper mantle resulted from the asthenosphere.The upper crust faults are

关 键 词：张渤构造带 深地震反射剖面 地壳精细结构 深断裂 

分 类 号：P315[天文地球—地震学]