震源因素对尾波干涉提取经验格林函数的影响  

Influence of source factors on extracting empirical Green′s functions by coda interferometry

作　　者：冯旭平 王涛 FENG XuPing;WANG Tao(Institute of Geophysics and Geodynamics (IGG), School of Earth Sciences and Engineering,Nanjing University, Nanjing 210046, China)

机构地区：[1]南京大学地球科学与工程学院地球物理和动力学研究所

出　　处：《地球物理学报》2019年第9期3408-3420,共13页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41774046,41674048)资助

摘　　要：尾波干涉提取经验格林函数作为现今地震学一项重要的研究,其受震源因素的影响值得细致地探讨.本文通过模拟和实际数据的尾波干涉,系统性讨论了震源倾角、方位角和走向以及震中分布对于提取经验格林函数(主要是PKIKP^2和PKIIKP^2震相)的影响.我们发现PKIKP^2震相的平均信噪比随倾角的增大呈现先增大后减小的变化趋势,并在倾角约为45°时达到最大.基于稳相点分析,本文认为这种变化趋势是因为提取的PKIKP^2震相主要贡献来源于近乎径向方向,而倾角为45°的倾滑型断层事件辐射出的P波能量在径向上最大.此外,断层走向对尾波干涉提取Rayleigh面波并无明显影响,而方位角的影响非常显著.当事件近似在台站对的大圆弧上时,尾波干涉才能提取清晰的Rayleigh面波,这与面波稳相区的空间分布一致.对于PKIKP^2和PKIIKP^2震相,只有当事件分布与台站对大圆弧近垂直并且事件断层走向与线状台阵近平行时,才能提取清晰的波形.通过计算不同事件和台站分布的震源辐射能量,上述方位角和走向最有利于地核震相的提取.最后,震中分布对尾波干涉提取PKIKP^2震相也有一定的影响:当震中与地心连线和PKIKP^2震相射线路径之间的锐角夹角越小,并且震中距越小时,提取的地核震相的信噪比越高.Coda interferometry is an effective approach to retrieve empirical Green′s functions and the influence of source factors is important to apply the interferometry.Through cross correlations of synthetics and real coda,we systematically analyze the effects of dip angle,azimuth and strike,and epicenter distribution on the extraction of empirical Green′s functions(mainly the PKIKP^2 and PKIIKP^2 phases).Our results infer that the average signal-to-noise ratios of PKIKP^2 phase firstly increase,then decrease with the dip-angle increasing,and reach the maximum at the middle dip angle(~45°).Based on the analysis of the stationary point,this trend may be due to the fact that the major contribution of the extracted PKIKP^2 phase is from the radial direction,while radiated energy along the radial direction from the dip-slip earthquake is the largest when the dip angle is ~45°.Moreover,the extraction of Rayleigh waves severely depends on theazimuth but is not affected by the strike.When the epicenters locate near the great circle arc of the station-pairs,coda interferometry can retrieve clear Rayleigh wave,which is consistent with the stationary phase region of surface waves.For the PKIKP^2 and PKIIKP^2 phases,high signalto-noise ratios of the waveforms can be reconstructed only when the epicenters are far away from the great circle arc of the station-pairs and the strike of the faults is nearly parallel to the linear array.Our calculation of the source radiation energy,to some extent,demonstrates that above setting of the azimuth and the strike can improve the retrieval of two core phases.Lastly,epicenter distribution can influence the extraction of the PKIKP^2.The smaller the acute angle between the radial direction of the earthquake and the raypath of the PKIKP^2 phase is,as well as the smaller distance,the higher the signal-to-noise ratios can be acquired.

关 键 词：尾波干涉 震源机制解 震中分布 PKIKP^2震相 经验格林函数 

分 类 号：P315[天文地球—地震学]