Fig. 7

a Gaussian filters for various separation distances at 0.1 Hz. b Gaussian filter for \(r = 200\) km. c FTAN diagram for a synthetic CCF with the observation error is 1%. The separation distance is \(r = 200\) km. The black line shows the theoretical group velocity and the red dots show measured values using synthetic data. d Group and phase velocity anomalies for the synthetic CCFs with 1% measurement errors as a function of separation distance at 0.1 Hz. e Measured phases (blue dots) and the theoretical values (dashed lines) at 0.1 Hz. f Histogram of group and phase velocities estimation errors at 0.1 Hz