The time-distance diagram represents the recording of a simulated seismic wave (a seismic section). The vertical axis represents a receiver's distance in relation to the source, the horizontal axis represents the recording length. The slope of the wave is a function of the propagation velocity of sound in the medium concerned. It is represented here by the delay of a wave's arrival time between two receivers.
After application of a double Fourier transform over time and distance variables, the seismic recording is represented by its modulus in the frequency-wavenumber plane (F,K plane). The velocity is obtained from the f/k relationship.
On the left from top to bottom:

• The f,k section (frequency, wavenumber) for the positive frequencies; the initial content in frequency domain of the seismic trace have a maxima at 0.2 Hz,
• The time-distance section;

On the right,

• the f,k section (frequency, wavenumber) for the positive and negative frequencies.

We can choose the delay between two consecutive traces.
We can sub-sample 2 or 4 times in time domain. Within these conditions, the Shannon limit is not respected. The presentation on the right allows us to show how evident the effect of periodisation is in frequency (vertical axis).