Color sonagrams: A new dimension in seismic data interpretation

We have developed a computer-graphic-photographic system which uses color mimicry to display the frequency spectra of seismic events simultaneously with their time-varying waveforms. Mimicking the visible light spectrum, we have used red for the low frequencies and violet for the highs. The output of our system is a variable-area-wiggletrace seismic cross-section. The waveforms are the same as those on a conventional section; however, the variable-area part of the section appears in color. The color represents the frequency spectrum of the wavelets. Lateral changes in rock attenuation show up as color shifts on this type of display. Faults often stand out as interrupted color bands. Fault diffractions sometimes have a characteristic color signature. The cancellation of high frequencies due to misalignment of events on constant-velocity stacks can show up in color. Loss of high frequencies due to slight lateral changes in moveout velocity, and consequent trace misalignment, is often indicated by a shift toward red on a color seismic section.