Fig. 8

Group and phase velocities and the average spectrogram of raw data. Gray-scale filled contours represent the averaged spectrograms of all the CCF that met the SNR requirements, where the maximum value for each period in the individual spectrograms was normalized to one. The fundamental and second mode Rayleigh wave is visible in these data as the broad regions. Filled black circles with error bars indicate the average group velocities for the fundamental mode, while open circles with error bars indicate the average group velocities for the higher-mode Rayleigh wave. Black triangles with error bars indicate fundamental mode uncorrected phase velocities; gray triangles with error bars indicate \(-\pi /4\) corrected phase velocities for higher and fundamental mode phase velocities, and open triangles with error bars indicate higher mode phase velocities. Taken from Harmon et al. (2007)