张北地震区三维深部电性结构与孕震环境  

3D deep electrical structure and seismogenic environment in Zhangbei earthquake region

作　　者：彭远黔[1] 孙翔宇[2,3] 詹艳 赵凌强[4] 刘雪华 冉志杰 王莉森 PENG YuanQian;SUN XiangYu;ZHAN Yan;ZHAO LingQiang;LIU XueHua;RAN ZhiJie;WANG LiSen(Hebei Earthquake Agency,Shijiazhuang 050021,China;State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;Shanxi Taiyuan Continental Rift Dynamics National Observation and Research Station,Beijing 100029,China;The Second Monitoring and Application Center,China Earthquake Administration,Xi'an 710043,China)

机构地区：[1]河北省地震局,石家庄050021 [2]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [3]山西太原大陆裂谷动力学国家野外科学观测研究站,北京100029 [4]中国地震局第二监测中心,西安710043

出　　处：《地球物理学报》2022年第9期3464-3480,共17页Chinese Journal of Geophysics

基　　金：国家重点研发计划(2017YFC1500103);中国地震局地质研究所基本科研业务专项(IGCEA2215);河北省省级科技计划(19975412D);山西太原大陆裂谷动力学国家野外科学观测研究站资助项目(NORSTY20-07)共同资助。

摘　　要：张家口—渤海地震构造带(张渤带)是中国著名的强震集中带,地震以强度大、频次高、破坏严重为特点,1998年1月在张渤带西段发生了张北6.2级地震,造成了极强的破坏性,2021年以来该区域中小地震频繁发生,显示出张渤带张北地震区可能进入了又一轮的地震活跃态势.2020年8—9月期间,以张北地震震中区为中心,完成了阵列状的大地电磁数据采集工作.本文利用这些数据进行三维反演计算获得了该区域精细三维地壳电性结构,获得了如下认识:整体上看,张北地震区上地壳电性结构以高阻体为主,部分断裂带分布区域存在着高阻、低阻相互交替的现象,而中下地壳以规模较大、横向不连续性的低阻层为主.电性结构特征与地表地质构造格局相对应,大满—前黑沙土断裂(F1)和赤城—尚义断裂(F4)以及张家口断裂(F5)在电性结构上均表现为明显的电性差异带.针对地震学方法对1998年张北地震震源深度的多种定位结果,大地电磁探测结果支持震源深度位于12~15 km之间;发震断裂可能为隐伏在汉诺坝玄武岩区下方的大河镇—海流图断裂(F3).通过此次获得的三维电性结构信息,结合张北地震震源参数、震源机制解以及前人地震地质和地球物理探测结果综合分析,认为该区的上地壳高阻体代表着刚性较强的汉诺坝玄武岩区,汉诺坝玄武岩区下方的低阻体代表着地幔岩浆热物质,这些地幔热物质持续的向上侵入和上涌作用可能会削弱汉诺坝玄武岩区内发育的断层稳定性,直到累积足够的应力,产生了非均匀应力积累和变形并弱化了断层强度,导致了张北地震的发生.鉴于张北地震区深部具有的特殊构造环境,该地区仍然是张渤带未来应该长期关注的地震危险重点区域.The Zhangjiakou-Bohai seismic tectonic zone(Zhangbo zone)is a concentration zone of strong earthquakes in China.Earthquakes in the Zhangbo zone are characterized by great intensity,high frequency,and serious damage.In January 1998,Zhangbei M6.2 earthquake occurred in the western segment of the Zhangbo zone,causing significant damage.Since 2021,small and medium earthquakes have occurred frequently in this region,indicating that the Zhangbei earthquake region in the Zhangbo zone may have entered another round of seismicity.The resistivity structure in the Zhangbei earthquake region and its adjacent areas is obtained through the application of the magnetotelluric(MT)method.Field acquisition of 67 MT stations was completed in the epicentral region of the Zhangbei earthquake from August to September 2020.The detailed 3D crustal resistivity structure is obtained by using these data.The characteristics of the resistivity structure and seismogenic environment of the Zhangbei earthquake are analyzed.On the whole,the resistivity structure of the upper crust in the Zhangbei earthquake region is mainly composed of high resistivity bodies.There is alternating high and low resistivity in some fault zones.The middle and lower crust is dominated by large-scale and transversely discontinuous low resistivity zones.The resistivity structure characteristics correspond to the surface geological structure.The Daman-Qianheishatu fault(F1),the Chicheng-Shangyi fault(F4)and the Zhangjiakou Fault(F5)show obvious differences in the resistivity structure.The magnetotelluric results support that the focal depth of the Zhangbei earthquake was between 12 and 15 km.The seismogenic fault is the Dahezhen-Hailiutu fault(F3)which is buried beneath the Hannuoba basalts.The 3D resistivity structure information was combined with the source parameters,focal mechanism,seismic geology,and geophysics results of the Zhangbei earthquake.It is believed that the high resistivity body in the upper crust of this area may represent the Hannuoba basalts with stro

关 键 词：张北M6.2地震 张家口—渤海地震构造带 大地电磁 深部结构 

分 类 号：P319[天文地球—固体地球物理学] P315[天文地球—地球物理学]