The Role of Seismic Wavelets and Wavelet Processing
Use of waveforms is a natural extension of using seismic amplitudes and also a part of our approach to interpretation in the ideal case. Waveforms, in fact, include both amplitude information as a function of frequency and phase as function of frequency. Phase is a rather subtle concept which relates to the alignment in time of the frequency components.
We first consider an exhibit provided by Lindseth and Petty-Ray Geophysical Co. which shows the amplitude content of a complete seismic record and a single Ricker wavelet as functions of frequency. Much of our thinking has been directed toward the precept that the resolution potential, and hence the interpretive potential of a seismic waveform rests with the broadness of its frequency band. Hence, waveforms which encompass much high frequency must permit highly resolved interpretations. While these ideas are true, they do not express the entire circumstance. The shape of the waveform and its corresponding phase structure are of equal if not of greater interpretive significance.
We first encountered the significance of waveform shape in developing the interpretive scheme for an ideal subsurface. Where the zero phase-symmetric waveform was present we could identify individual reflection events and accomplish much that was not possible with a more complex waveform. Schoenberger of Exxon (1974) and Berkhout (1973, 1974), who was with Shell at the time, both recognized the merits of the simple waveform and were even able to express this in theoretical terms.
In the figure which follows we outline the transformation of a
Figures & Tables
Stratigraphic interpretation of seismic data requires that the seismic information be expressed in geological terms. The strictly geological view of the earth is developed from surface observations, guiding principles of geological evolution and subsurface information from bore holes. Seismic measurements on the other hand, define in some sense the subsurface geometry and give estimates of the acoustic impedance which is related to the rock velocities and densities. This publication contains eight chapters on: relating seismic data to stratigraphy; information content and resolution potential of seismic data; processing for preservation of seismic amplitudes; the role of seismic wavelets and wavelet processing; contributions of geoseismic modeling; qualitative stratigraphic correlations; quantitative stratigraphic correlations; and conversion of seismic data to log-like displays.