利用背景噪声资料研究海原断裂带及邻区Rayleigh波相速度和方位各向异性  

Rayleigh Wave Phase Velocity and Azimuthal Anisotropy across Haiyuan Fault Zone and Its Adjacent Area Derived from Ambient Noise Tomography

作　　者：车子强 吴忠良 高原[1] CHE Zi-qiang;WU Zhong-liang;GAO Yuan(Key Laboratory of Earthquake Prediction,Institute of Earthquake Forecasting,China Earthquake Administration,Beijing 100036,China)

机构地区：[1]中国地震局地震预测研究所(地震预测重点实验室),北京100036

出　　处：《地震》2023年第1期105-123,共19页Earthquake

基　　金：国家自然科学基金项目(42074065);国家自然科学基金地震科学联合基金项目(U2039207)。

摘　　要：海原断裂带是位于青藏高原东北缘的一条NWW走向大型边界断裂带,为了研究该区域地壳速度结构与变形特征,使用中国地震局地震预测研究所布设的跨海原断裂带流动地震台阵(SACHY-Array)和研究区域内固定地震台站共61个台站(40个流动台站和21个固定台站)的垂向连续波形数据.采用背景噪声互相关方法,提取了面波相速度频散曲线,反演得到周期范围为5~30 s、分辨率1°×1°的Rayleigh波相速度和方位各向异性图像.结果表明,短周期5~10 s内,河西走廊过渡带东部、鄂尔多斯地块西北部以及银川地堑南部均呈现低速异常体,祁连造山褶皱带东段表现为相对高速体;海原断裂带西南侧快波偏振方向为NWW、NW向,鄂尔多斯西缘及邻区快波偏振方向主要为近NS向,各向异性方向与区域断裂走向基本一致.15~30 s周期内,河西走廊过渡带东部及银川地堑南部的低速异常逐渐减弱且范围不断减小,15 s周期左右,河西走廊过渡带东部的低速体在烟筒山断裂带下方有错断的趋向,陇中盆地中央、鄂尔多斯西南缘均存在高速异常体;方位各向异性方向与短周期基本一致,不过各向异性强度较弱.本文认为,海原断裂带是高低速过渡带,位于断裂带北侧的河西走廊过渡带表现为低速异常,而位于南侧的祁连褶皱造山带表现为高速异常,海原断裂带及邻区具有复杂的地壳结构,并可能存在局部的地壳破坏变形;地壳方位各向异性作为地壳变形的重要约束指标,说明了海原断裂带及邻区各向异性可能主要由青藏高原东北缘地壳的剪切变形所产生,青藏高原的NE向推挤作用是这一地区的主要动力来源.Haiyuan fault zone is a large NWW-trending boundary fault zone located on the northeastern margin of the Qinghai-Tibet Plateau.In order to study the crustal velocity structure and deformation characteristics of this region,the Cross-Haiyuan Fault Zone temporary Seismic Array set up by the Institute of Earthquake Forecasting,China Earthquake Administration(SACHY-Array)and vertical continuous waveform data of a total of 61 stations(including 40 temporary stations and 21 permanent stations)in the study area were used.Based on the background noise cross-correlation method,the surface wave phase velocity dispersion curves were extracted,and the Rayleigh wave phase velocity and azimuth anisotropy images with a period range of 5~30 s and a resolution of 1°×1°were obtained by inversion.The results show that,within a short period of 5~10 s,the eastern Hexi Corridor transition zone,the northwestern Ordos Block,and the southern Yinchuan graben all present low-velocity anomalies,while the eastern Qilian orogenic fold belt presents relatively high-velocity;the southwest side of the Haiyuan fault zone presents fast waves the polarization directions are NWW and NW.The polarization direction of fast waves in the western margin of Ordos Block and its adjacent areas is mainly near NS,and the anisotropy direction is basically consistent with the regional fault strike.In the period of 15~30 s,the low-velocity anomalies in the east of the Hexi Corridor transition zone and the southern part of the Yinchuan Graben gradually weakened,and the range continued to decrease.Around the 15 s period,the low-velocity bodies in the east of the Hexi Corridor transition zone were staggered under the Yantongshan fault zone.There are high-speed anomalies in the center of the Longzhong Basin and the southwestern margin of Ordos;the direction of azimuthal anisotropy is basically consistent with the short period,but the anisotropy intensity is weak.The authors believe the Haiyuan fault zone is a transition zone between high and low velocities.The Hex

关 键 词：海原断裂带 流动地震台阵 背景噪声成像 Rayleigh波相速度 地壳 方位各向异性 

分 类 号：P315.7[天文地球—地震学]