利用背景噪声互相关观测近对跖点台站间体波格林函数

本文利用秦岭周边和南美地区的部分台站2012-2014年记录的地震事件垂直分量数据,获取了166个台站对之间的互相关函数,从中观测到了近对跖点台站之间的体波格林函数.在此基础上,我们计算了理论地震图的互相关,其结果与实际数据获得的结果很相似,推测格林函数的能量来源应主要是大地震引起的地球自由振荡.更进一步的研究表明,不同的震源机制对于互相关结果中不同震相的振幅有较大影响,走滑断层引起的地震并不能产生较好的互相关结果.通过对比不同位置台站对的互相关结果,本文认为互相关得到的体波格林函数包含了传播路径信息.

Green functions between antipodal station pairs from cross-correlation of ambient noises

Ambient-noise cross-correlation is widely used to retrieve the Green function between two seismic stations. The Green functions of several body-wave phases between two near antipodal stations can be extracted by cross-correlating the coda waves of large earthquakes. In this study, we cross-correlate the data from Peking University temporary seismic arrays and China provincial seismic network in the Qinling and the data from the GSN (Global Seismographic Network) stations in South America to retrieve body-wave Green functions. The cross-correlation result clearly shows several body-wave phases (e.g., PKIKP, PP, PcPPKP, SKSP). Meanwhile, very similar Green-function waveforms can be retrieved by cross-correlating the synthetic seismograms generated from a 1D Earth model. This result suggests that free oscillations (normal modes) generated by large earthquakes are the most important energy source for the body-wave Green functions. The synthetic test also indicates that focal mechanism can influence the correlation result, e.g. the PKIKP phase cannot be observed if only strike-slip events are stacked. Our results suggest that by rejecting strike-slip events during the processing, we can increase the signal-to-noise ratio of the Green functions and reduce the computation time. Our study provides an example to demonstrate that the body-wave Green function may contain heterogeneity information of the Earth.