The Effect of Temporal Variations of the Ambient Noise on the Retrieved Surface and Reflected Waves

The ambient noise parameters vary in time, especially when the passive measurements are performed in different surveys. These variations can be seen on the amplitude spectra of the noise and on the retrieved surface and body-wave reflected waves using the Seismic Interferometry by crosscorrelation. In this study, I analyze the temporal variations of the ambient noise recorded in two separate surveys performed at two months apart and I compare the parameters (frequencies, apparent velocities) of the retrieved surface and body-wave reflected waves. Comparing the amplitude spectra of the ambient noise recorded in both datasets for the same time windows (1 hour and 2 hours), I notice higher amplitudes on the frequency interval corresponding to the body-wave reflected waves on the second dataset. According to the analysis of the interferometry results, the surface waves recorded in the first passive survey are richer in higher frequencies than those recorded in the second passive survey. The retrieved body-wave reflected waves show similar parameters, especially on the first 0.5 seconds from the virtual common-source gathers. The frequency interval of 12–23 Hz used for band-pass filtering was chosen based on the analysis of the active seismic data recorded in the vicinity of the passive surveys.