# Dictionary:*f-k* domain

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The **frequency-wavenumber domain** in which the independent variables are frequency (*f*) and wavenumber (*k,*) the result of a 2D Fourier transform of a seismic record or seismic section; *f-k***space**. Seismic data analysis sometimes involves *f-k***plots** (see Figure F-11) in which energy density within a given time interval is contoured on a frequency-versus-wavenumber basis. Used to examine the direction and apparent velocity of seismic waves and in velocity-filter design.

FIG. F-11.
*f,k***plot**. (**a**) The region passed by array, frequency, and velocity filters is cross-hatched. Radial lines through the origin represent constant apparent velocity *V*_{a} (*V*_{a}=*f*/*k*=ω/κ). (**b**) Data beyond the Nyquist wavenumber *f*_{N} (determined by discrete spatial sampling) **wraps around** (**aliases**) and may get mixed up with the signal. In wraparound, data to the right of +*k*_{N} continues rightward from –*k*_{N}, where *K*_{N} is the Nyquist wavenumber.