Improvement in the Empirical Green’s Function Extraction Using Root Mean Square Ratio Stacking

Seismic interferometry is an efficient technique to extract the Empirical Green’s Function (EGF) between station pairs when the source is considered at one of the stations. The geometry and energy flux of asymmetric noise sources have unavoidable impacts on the extracted EGFs, deduced from ambient seismic noise recorded in pairs of stations. In this study, to consider these effects, three methods of noise correlation functions stacking (linear, root mean square, root mean square ratio) are investigated using synthetic and real data processing. During synthetic data processing, effects of the noise sources geometry and energy flux inside and outside the Fresnel zone are examined. After separating stationary and nonstationary sources, the results have shown that the root mean square ratio contains the least effects of nonstationary signals compared to other methods of stacking. Moreover, comparison of the EGFs from the recorded data in Azerbaijan (NW Iran), indicates that the signal retrieved by root mean square ratio is more reliable than the other stacking methods’ signals (e.g., linear, root mean square).