A new stacking technique in ambient noise tomography

We have developed a new stacking technique in ambient noise tomography to obtain high-quality dispersion curves of Rayleigh waves. This technique is used to stack the vertical components of the Estimated Green Functions (EGFs) obtained respectively from cross correlation of the ambient noise data recorded by a remote seismic station and one of the short distance seismic stations of a seismic array. It is based on a phase-matched filter and is implemented by a four-step iterative process: signal compression, stacking, signal extraction and signal decompression. The iterative process ends and gives the dispersion curve of Rayleigh wave when the predicted one and the processing result converge. We have tested the method using the vertical components of synthetic Rayleigh wave records. Results show that this new stacking method is stable and it can improve the quality of dispersion curves. In addition, we have applied this method to real data. We see that the results given by our new technique are obviously better than the ones employing the traditional method which is a three-step process: signal compression, signal extraction and signal decompression. In conclusion, the new method proposed in this paper can improve the signal to noise ratio of EGFs, and can therefore potentially improve the resolution of ambient noise tomography.