Sampling > Respected Shannon limit

A seismic function whose frequency content is restricted by a maximum frequency Fm must be sampled with a sampling frequency Fe that is greater than 2 Fm. This condition is called the "Shannon condition". In effect, if a function, sampled at a frequency Fe, has a frequency content restricted by Fm, it can be sub-sampled by a factor n (n < Fe/2Fm). A sub-sampling of order n (2 for example) only conserves every 1 point out of n (1 out of 2). The new sampling frequency is now Fe/n. The modulus of the FT of the sub-sampled signal is present between 0 and Fe/2n, which is the new Shannon limit.