基于密集线性台阵的背景噪声成像在明光市城市活断层调查中的应用  

Application of ambient noise tomography with a dense linear array in prospecting active faults in the Mingguang city

作　　者：倪红玉[1,3] 郑海刚 赵楠[1,3] 邓宝 缪鹏[1,3] 黄显良 李俊伦 NI HongYu;ZHENG HaiGang;ZHAO Nan;DENG Bao;MIAO Peng;HUANG XianLiang;LI JunLun(Anhui Earthquake Agency,Hefei 230031,China;School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;Mengcheng National Geophysical Observatory,Mengcheng Anhui 233500,China)

机构地区：[1]安徽省地震局,合肥230031 [2]中国科学技术大学地球和空间科学学院,合肥230026 [3]安徽蒙城地球物理国家野外科学观测研究站,安徽蒙城233500

出　　处：《地球物理学报》2022年第7期2518-2531,共14页Chinese Journal of Geophysics

基　　金：安徽省自然科学基金(2108085MD137);中国地震局地震科技星火计划(XH20026);安徽省重点研究与开发计划(2022m07020002);中央高校基本科研业务费专项资金(WK2080000141)共同资助。

摘　　要：近年来,短周期密集台阵被动源探测技术逐渐成为地壳精细结构探测研究中的重要手段.为了探讨其应用于城市活断层调查在勘探尺度的有效性,在横跨安徽省明光市郯庐断裂带东界两条主干断裂位置,沿同期的主动源S波反射剖面,安徽省地震局和中国科学技术大学联合布设了一条由133个短周期地震仪组成的被动源密集测线.我们通过该被动源测线获得了约28天的连续波形记录,并采用一种新的线性台阵背景噪声成像方法——拓距相移法提取了10 Hz~2.0 s宽频的基阶Rayleigh波相速度频散曲线.利用得到的宽频带频散曲线,我们反演了近地表1.3 km以浅的高分辨率S波速度结构,并与基本重合的主动源S波反射剖面以及地质资料等进行对比,验证了反演结果的可靠性,同时进一步分析了郯庐断裂带东界两条主干断裂的断层特征.结果表明:(1)被动源与主动源反演结果在近地表100 m以浅高度一致,且被动源的反演深度更深;(2)池河—太湖断裂是隐伏于深部的走滑断裂和浅部伸展断裂的综合反映,浅部为倾向北西的正断层,向上穿透第四系地层,可能为活动断裂;(3)拓距相移法能有效拓宽频散曲线的提取频带,保证浅部结构具有高分辨率,同时大大加强对深部结构的约束.该方法能够获得可靠的地下结构反演结果,可以作为城市活断层调查的一种新的有效手段.In recent years,the passive seismic techniques based on short-period dense arrays have gradually become an important measure in fine structure characterization.To study its effectiveness in prospecting active faults in urban areas in exploration scales,we deployed a seismic linear array consisting of 133 short-period nodes in the urban area of the Mingguang City,Anhui Province,which spans across the Jiashan-Lujiang fault and the Chihe-Taihu faults,which are two main faults in the eastern Tanlu fault zone.A shallow active seismic profiling in the same area was also carried out during the same period.Cross-correlations of the ambient noise data of about 28 days from the vertical components of different station pairs were computed in one-hour segments and stacked.We extracted the fundamental mode,broadband phase velocity dispersions of the Rayleigh surface waves from 10 Hz to 2 seconds using a recently proposed method named the extended range phase shift method.The S-wave velocity structure with high resolution from the surface down to about 1.3 km in depth was inverted for,and the reliability of the inversion results was also verified by comparing the results with the nearly overlapping S-wave reflection profile from the active survey,and with the local geological data.The characteristics of the Tanlu fault zone on the eastern boundary were further analyzed.The results indicate that:(1)The inverted results of passive source and active source are consistent from the surface down to about 100 m in depth,while the reliably characterized depth with the passive sources is greater;(2)the Chihe-Taihu fault is an aggregated reflection of a deep concealed strike-slip fault and a shallow extension fault,the shallow part of which is a N-W trending normal fault penetrating through the quaternary formation and may be an active fault;(3)the extended range phase shift method can effectively broaden the frequency band of the dispersion curve,which not only can obtain high resolution shallow structures,but also can greatly improve

关 键 词：密集线性台阵 背景噪声成像 浅层速度结构 拓距相移法 郯庐断裂带 城市活断层 

分 类 号：P315[天文地球—地震学]