Extracting surface wave dispersion curves from asynchronous seismic stations: method and application

Correlation of the coda of Empirical Green's functions (EGFs) from ambient noise can be used to reconstruct EGFs between two seismic stations deployed different periods of time. However, such method requires a number of source stations deployed in the area surrounding a pair of asynchronous stations, which limit its applicability in cases where there are not so many available source stations. Here, we propose an alternative method, called two-station C² method, which uses one single station as a virtual source to retrieve surface wave phase velocities between a pair of asynchronous stations. Using ambient noise data from USArray as an example, we obtain the interstation C² functions using our C² method and the traditional cross-correlation functions (C¹ functions). We compare the differences between the C¹ and C² functions in waveforms, dispersion measurements, and phase velocity maps. Our results show that our C² method can obtain reliable interstation phase velocity measurements, which can be used in tomography to obtain reliable phase velocity maps. Our method can significantly improve ray path coverage from asynchronous seismic arrays and enhance the resolution in ambient noise tomography for areas between asynchronous seismic arrays.