Feng X P, Wang T*
Chinese J. Geophys. (in Chinese)
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 PKIKP2 and PKIIKP2 phases). Our results infer that the average signal-to-noise ratios of PKIKP2 phase firstly increase, then decrease with the dip-angle increasing, and reach the maximum at the middle dip angle (~45o). Based on the analysis of the stationary point, this trend may be due to the fact that the major contribution of the extracted PKIKP2 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 ~45o. Moreover, the extraction of Rayleigh waves severely depends on the azimuth 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 PKIKP2 and PKIIKP2 phases, high signal-to-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 PKIKP2. The smaller the acute angle between the radial direction of the earthquake and the ray path of the PKIKP2 phase is, as well as the smaller distance, the higher the signal-to-noise ratios can be acquired.