Fourier Spectrum

The Fourier transform of the signal.

The Fourier transform of the signal a(t) is defined as follows:

Generally A(f) is a complex function. The modulus of the Fourier transform is denoted as the Fourier Spectrum of the signal a(t):

where R and I are the real and imaginary part of A(f), respectively.

Fourier Spectra of increasing magnitude accelerograms, recorded in 1985-1986 by digital instruments located on the Pacific coast of Mexico (Guerrero network).