| Analysis of the temporal and spatial variations in the overall raw amplitude and frequency content of deep seismic reflection data provides new clues to subsurface geology and data quality. Amplitudes and frequencies are efficiently derived by means of complex seismic trace analysis and can be smoothed in both time and space to enhance general trends. To preserve as much as possible the raw amplitude and frequency content of the data, ungained, unfiltered, and undeconvolved "true amplitude" stacks are used throughout. The theoretical influence of attenuation, stationary random noise, and normal moveout corrections are readily computed.; Seventeen deep seismic reflection lines from the COCORP (Consortium for Continental Reflection Profiling) data set were analyzed. Distinct decreases in amplitude with corresponding decreases or increases in average frequency to levels set by the ambient noise are found at Moho record times on three lines; similar though less clear anomalies are found on three others. This is interpreted as evidence of a transparent uppermost mantle, suggesting possible geologic homogeneity. The lack of such anomalies on the remaining lines investigated is largely attributable to lack of signal penetration. No attenuation "shadows" are found on any line, which is evidence only for the lack of thick bodies of low {dollar}Q{dollar}, for thin low-{dollar}Q{dollar} bodies could well exist but escape detection by this technique. Numerous artifacts of surface conditions, traffic noise, and data processing, which are not obvious on conventional displays, are revealed by analysis of amplitudes and frequencies.; The Surrency bright spot is possibly the brightest basement reflection ever recorded by COCORP. Modeling suggests that it is from a relatively thin synformal reflector with a buried focus. A strong multiple train obscures primary reflections beneath it and prevents the recognition of a low frequency shadow, if one exists. Its brightness is attributed to a great impedance contrast, thin-bed tuning, uncommonly good stack quality, and a relatively greater lateral extent than neighboring reflectors, which are short with respect to the relevant Fresnel zone radius. The presence of fluids or crystal-scale faults is not required to explain its brightness or geometry. |
