基于改进的多分量频率-贝塞尔变换法研究郯庐断裂带潍坊段上地壳径向各向异性结构  

Upper-crustal radial anisotropy beneath the Weifang segment of the Tanlu fault zone using the modified multicomponent frequency-Bessel transform method

作　　者：周桂理 罗松 姚华建[1,2] ZHOU GuiLi;LUO Song;YAO HuaJian(School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;Mengcheng National Geophysical Observatory,University of Science and Technology of China,Mengcheng Anhui 230026,China)

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

出　　处：《地球物理学报》2024年第3期1037-1052,共16页Chinese Journal of Geophysics

基　　金：中国自然科学基金委项目(42125401,42004031);中国地震局地震预测研究所重点实验室基础研发项目(2021IEF0103);安徽省自然科学基金(2108085QD174);中央高校基本科研业务费专项资金(KY2080000103)资助。

摘　　要：郯庐断裂带潍坊段位于郯庐断裂带中部,具有复杂的地质结构,总体呈现“两堑夹一垒”的构造格局.相比于郯庐断裂带其他区域,潍坊段地震活动性较弱,属于地震空区,未来发生大地震的可能性尚不明确.前人对该地区的研究目前仅局限于速度结构和方位各向异性结构,对于上地壳径向各向异性结构特征鲜有报道.因此,研究该区域上地壳速度模型和径向各向异性结构,有助于更好地认识郯庐断裂带潍坊段浅地壳(<10 km)变形特征,评估该区域发生地震的可能性.我们利用2017年在潍坊段所布设的302个短周期地震仪采集的背景噪声数据,基于改进的多分量频率-贝塞尔变换(MMFJ)法,同时提取到潍坊段东南侧四个区域子阵列的Rayleigh波和Love波的基阶及高阶频散数据,并且进一步反演这些频散数据得到了SV波和SH波速度以及径向各向异性结构.数值实验结果表明,高阶模式频散数据的加入能够降低反演的非唯一性,更好地约束浅地壳径向各向异性结构.实例中的径向各向异性结果表明,郯庐断裂带潍坊段四个区域都有近似相同的变形特征:在约2 km以浅,径向各向异性为负(V_(SH)<V_(SV)),这可能主要源于潍坊段垂向断裂结构的控制作用;5~7.5 km,径向各向异性为正(V_(SH)>V_(SV)),这可能与早期地壳伸展沉积导致的水平变形结构有关.2~5 km,四个区域径向各向异性结构各有不同,但总体处于由负到正的转折状态.这可能因为2~5 km不仅受到断裂结构的控制作用,也受到水平沉积结构的影响,导致径向各向异性结构较为复杂.The Weifang segment of the Tanlu fault zone is located in the middle part of the Tanlu fault zone,which has a complex geological structure and presents a structural pattern of"two garbens and one horst".In comparison to other areas of the Tanlu fault zone,the seismic activity of the Weifang segment is relatively weak,and it is considered a seismic gap with unclear potential for a future large earthquake.Previous studies on this area are limited to velocity structure and azimuthal anisotropy structure,with little research conducted on the radial anisotropy structure of the upper crust.Therefore,investigating the velocity model and radial anisotropy structure of the upper crust in this region can help us better understand the deformation characteristics of the shallow crust(<10 km)in the Weifang segment of the Tanlu fault zone and evaluate the likelihood of earthquakes.Using the ambient noise data recorded by 302 short-period stations employed in the Weifang segment in 2017,we extracted the fundamental and higher-mode dispersion data of Rayleigh wave and Love wave of four sub-arrays in the southeast of the Weifang segment based on the modified multicomponent frequency-Bessel transform(MMFJ)method.The velocity of the SV wave and the SH wave as well as the radial anisotropy are obtained by further inversion of these dispersion data.Numerical experiments show that the addition of higher-mode dispersion data can reduce the non-uniqueness of the inversion and better constrain the radial anisotropy of the shallow crust.The radial anisotropy results from field data indicate that the four sub-areas in the Weifang segment of the Tanlu fault zone exhibit similar deformation characteristics.At depths of 0~2 km,the radial anisotropy is negative(V_(SH)<V_(SV)),which may be mainly controlled by the effect of the vertical fault structure in the Weifang segment.At depths of 5~7.5 km,the radial anisotropy is positive(V_(SH)>V_(SV)),which may be related to the horizontal deformation structure caused by the early crustal extension te

关 键 词：改进的多分量频率-贝塞尔变换法 径向各向异性 郯庐断裂带 沂沭断裂带 背景噪声 

分 类 号：P315[天文地球—地震学]