Extraction of Group Velocity Dispersion Curves of Surface Waves Using Continuous Wavelet Transform

Surface wave tomography is performed by first estimating surface wave dispersion curves and then inverting them. The objective of this letter is the efficient and reliable estimation of the group velocity dispersion curves of surface waves. In this letter, group velocity dispersion curves of surface waves recorded at a single station with a known location of seismic source or between a pair of stations are estimated using continuous wavelet transform (CWT). The advantage of CWT is its multiresolution property and flexible choice of analyzing function. In the proposed method, the number of CWT filters used is almost half of the total number of filters used in the conventional frequency-time analysis (FTAN) method. The CWT coefficients of the seismogram are the functions of time and scale (analogs to wave period). The arrival time to reach the peak of the envelope function of CWT coefficients is estimated to calculate the group velocity of the surface waves. The group velocity dispersion curve of the surface waves is the plot of the change of group velocity with the period. Synthetic test data and ambient noise recordings of MesoAmerica seismic experiment (MASE) stations are acquired to investigate the performance of the proposed method. It is observed that the proposed method effectively retrieves the weaker surface waves and results in the broader band group-velocity dispersion curve when compared to the conventional FTAN method. The proposed method is also found to be computationally efficient.