Abstract: Geologic Interpretation of Color Displays of Complex Seismic Trace

R. E. Sheriff, M. T. Taner, D. Frye, F. Koehler

Seismic data contain much geologically meaningful information in addition to the arrival time and apparent dip of reflection. The extraction of stacking-velocity information and reflection amplitude are two types of geologically important information. Various attempts have been made to analyze variations in frequency and reflection-wavelet character with geographic position, but such techniques have not been applied extensively. One of the drawbacks to more application has been the inability to see changes in a quantitative manner where the relation of the changes to seismic structure was evident.

The Seiscom Delta attribute-analysis program regards the seismic trace as an analytic signal. Standard transform techniques generate the quadrature trace and one then can solve for the amplitude of the envelope of the seismic wave and its instantaneous phase. The amplitude of the envelope is called "reflection strength," it is not sensitive to the phase or polarity of the seismic signal and hence differs from the more familiar "amplitude" of the seismic trace. The instantaneous phase contains no amplitude information and emphasizes the continuity of data. It is a sensitive indicator of discontinuities such as those caused by faults, pinchouts, onlap and offlap, unconformities, the interference between coherent events, etc. The first time derivative of the instantaneous phase yields th "instantaneous frequency." The frequency weighted according to amplitude and then smoothed over a time window also is found to be a useful parameter.

The interpreter faces a problem in appreciating these many variables and seeing their interrelations. Display of auxiliary variable in the form of color superimposed on a normal black-and-white reflection section assists in comprehension. The quantitative use of color in the display of seismic data brings to an interpreter's attention variations in geology which are not otherwise evident.

With well-processed data which are relatively free of recording variations, changes in reflectivity indicate changes in the geology. Seischrome^TM displays permit the interpreter to focus on the exact points where changes occur and to determine the magnitude of the changes.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC