利用环境噪声自相关研究唐海—商都台阵测线下方的莫霍面深度  

Depth of Moho beneath the Tanghai-Shangdu seismic array profile from ambient noise autocorrelation

作　　者：魏红谱 赵爱华[1] Wei Hongpu;Zhao Aihua(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China)

机构地区：[1]中国地震局地球物理研究所,北京100081

出　　处：《地震学报》2024年第1期47-68,共22页Acta Seismologica Sinica

基　　金：科技部国家重点研发计划(2020YFA0710600);国家自然科学基金(41974065);中国地震局地球物理研究所基本科研业务费专项(DQJB19B40)共同资助。

摘　　要：基于唐海—商都宽频带地震台阵2006—2009年连续三年的波形记录,利用环境噪声相位自相关函数对台阵下方的莫霍面反射P波进行分析。通过对同一个台站多个时间段的自相关结果进行分组、采用两步叠加处理增加信号强度:(1)在组内进行线性叠加,对组间的叠加结果进行相位加权叠加;(2)基于华北地区的背景速度结构信息,在地壳平均速度5%不确定性的时窗内,根据自相关函数包络线的二阶导数最大值确定P波的莫霍面反射时间,经时间-深度转化,获得台阵下方的莫霍面深度。结果显示,莫霍面从东南向西北总体由浅变深,中间有小幅度的起伏。噪声自相关方法确定的莫霍面平均深度相较于参考的接收函数结果的偏差为0.8 km,相应的双程走时偏差约为0.3 s。以月份叠加的自相关函数结果显示,PmP信号的噪声源具有显著的季节性变化。自相关函数的波形特征显示华北地区的地壳-地幔转换带的速度梯度模式不同。Ambient noise encompasses both surface and body waves.Although surface-wave extraction is more common,the extraction of body waves is not as widespread,with its application in the Earth's deep subsurface exploration typically confined to regions with simpler geological structures.A linear broadband seismic array,deployed in the North China Craton,spans from the southeast(Tanghai) to the northwest(Shangdu) and traverses plain,mountainous,and plateau regions.This study endeavors to extract Moho-reflected P-waves(PmP) from three years of array recordings(2006–2009),with the extracted body waves utilized to determine the depth of the Moho interface beneath the array.The process of extracting PmP from ambient noise involves six steps.In the first step,continuous recordings of the vertical component of the PmP are divided into segments of 1 h durations.In the second step,the recorded segments undergo bandpass filtering in a frequency range of 2-4 Hz for most stations and 1-2 Hz for a select few.The third step involves phase autocorrelation of the filtered segments.In the fourth step,a two-step stacking process is applied to the phase autocorrelation functions from multiple time intervals at the same seismic station.A linear stacking is initially performed within the group of autocorrelation functions,followed by a phase-weighted stacking of the group results to generate a seismic trace.In the fifth step,the second-order derivative of the envelope of the stacked traces is computed.Finally,in the sixth step,within a time window containing vertically reflected P-waves from the Moho interface which is determined based on prior information(i.e.,Moho depth and assumed error of 5% in average crustal P-wave velocity),the time corresponding to the maximum value of the second-order derivative is selected.This time is converted to the Moho depth using the average crustal velocity.Following the six steps,the data from the Tanghai–Shangdu array are processed.In terms of the time window for P-wave selection,the prior Moho depth

关 键 词：华北地区 莫霍面深度 环境噪声 相位自相关 反射P波 

分 类 号：P315.2[天文地球—地震学]