赵玲云^1,3,,
王伟涛^1,2,,,
王芳^1,4,
李娜¹
1. 中国地震局地球物理研究所, 北京 100081
2. 中国地震局地球物理研究所震源物理重点实验室, 北京 100081
3. 云南省地震局, 昆明 650224
4. 中国科学院精密测量科学与技术创新研究院大地测量与地球动力学国家重点实验室, 武汉 430077

基金项目: 国家重点研发计划(2018YFC1504200), 国家自然科学基金(41674061和41842042), 大地测量与地球动力学国家重点实验室开放基金(SKLGED2020-5-2-E)和中国地震局地球物理研究所基本科研业务费专项资助(DQJB19B34)共同资助


详细信息

作者简介: 赵玲云, 女, 1995年生, 中国地震局地球物理研究所硕士研究生, 从事地震背景噪声研究.E-mail: 18487202725@163.com

通讯作者: 王伟涛, 男, 1979年生, 研究员, 主要从事背景噪声、主动震源等重复性震源研究.E-mail: wangwt@cea-igp.ac.cn

中图分类号: P315

收稿日期:2020-02-18
修回日期:2021-06-11
上线日期:2021-12-10

The distribution of noise source both in space and time and its influence on Noise Cross-correlation Functions

ZHAO LingYun^1,3,,
WANG WeiTao^1,2,,,
WANG Fang^1,4,
LI Na¹
1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
2. Key Laboratory of Earthquake Source Physics, Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
3. Yunnan Earthquake Agency, Kunming 650224, China
4. State Key Laboratory of Geodesy and Earth's Dynamics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430077, China


More Information

Corresponding author: WANG WeiTao,E-mail:wangwt@cea-igp.ac.cn

MSC: P315

--> Received Date: 18 February 2020
Revised Date: 11 June 2021
Available Online: 10 December 2021


摘要
摘要:噪声源的空间分布和季节变化会对噪声互相关函数中的信号产生一定影响.本文选取了ChinArrry二期台阵南部的322个宽频带地震台，利用其2013年9月至2016年6月的垂直分量连续记录计算了台站间的互相关函数，进而通过背景噪声能量流的方法，分析了周期频段4~8 s，8~12 s和12~20 s的噪声能量随时间的演化规律.结果表明，在不同频段，背景噪声的强度及优势来源方向均具明显的季节变化，且不同周期频段的噪声能量变化规律有所差异.总体而言，噪声能量在北半球冬季较强，夏季较弱，与全球海洋活动的季节性变化一致，能量优势来源方向也与全球海浪波高分布相符.同时，在10~20 s频段范围内，噪声互相关函数中存在较强的异常信号.该信号在环形台阵路径上的到时呈现随方位角的规律变化，且冬季较强，夏季较弱.基于走时的分析表明，该信号是由大西洋北部的一个强噪声源激发产生的.在特定路径上，该信号可能对频散提取产生干扰.研究表明，噪声源分布的不均匀性以及季节变化会对噪声互相关函数中信号的细节形态产生影响，进而影响格林函数的收敛程度，相关精细化研究应对噪声源的特性予以关注.
关键词: 噪声源分布/
噪声互相关函数/
背景噪声能量流

Abstract:The reconstruction of Green's function by long time ambient noise cross-correlation has been widely used in seismology. The distribution of noise sources doesn't meet the theoretical assumption that they are uniformly distributed in both space and time, which can affect signals retrieved from Noise Cross-correlation Functions (NCFs). To further address this issue, using the continuous vertical records of 322 broadband seismic stations which are evenly distributed in a square in southern part of ChinArray Phase II, we calculate the NCFs from September 2013 to June 2016. The seasonal variation and azimuthal anisotropy are analyzed using the normalized background energy flux (NBEF) method for the period bands 4~8 s, 8~12 s and 12~20 s, respectively. Clear seasonal variation and directional anisotropy are observed for all periods and the characteristics of different periods are variable. Overall, the ambient noise energy is stronger in winter and weaker in summer. This is consistent with global oceanic activities which are stronger in winter and become weaker in summer in each local hemisphere. Moreover, strong precursors are observed in NCFs for period 10~20 s, showing clear azimuthal dependency in the NCFs having similar inter-station distance and different azimuths. The precursors are stronger in winter and weaker in summer. Analyzing their seasonality and arrival time suggests that they should be caused by one local noise source located in the northern Atlantic Ocean. The precursors may generate strong signals just before the Rayleigh waves and distort the dispersion measurement. This study suggests that the characteristics of the noise source, such as uneven distribution and seasonal variation, will affect the detail of the signals in NCFs and further the convergence of the Green's function. This phenomenon should be to be considered in noise cross-correlation studies.
Key words:Ambient noise source distribution/
Noise Cross-correlation Function/
Normalized background energy flux



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