Detailed lithologic interpretation of seismic sections and/or pseudo‐sonic logs generated from seismic data requires that the seismic trace can be modeled as a reflection series convolved with a zero‐phase broadband wavelet. Ghosting and marine signature deconvolution processing is a prerequisite for assuring that the seismic wavelet on a marine CDP section will be zero phase. A deterministic approach to deconvolution is centered around the concept of abandoning the purely statistical method of wavelet estimation and actually measuring the seismic wavelet. A proper signature recording for marine data is, therefore, a crucial component of deterministic deconvolution. Another important element in the deterministic deconvolution sequence is the application of a deghosting filter to remove near‐surface reflections. Proper application of a deghosting filter significantly improves the correlation between log synthetics and the seismic trace. It has been found that statistical deconvolution schemes, because of the number of statistical hypotheses required to produce a deconvolution filter, produce residual wavelets that are highly variable in character and whose average phases cover the entire phase spectrum, modulo 2π. Examples of a Gulf Coast marine line which was shot with Aquapulse™, air gun, and Maxipulse™ sources by the RV Hollis Hedberg are presented to demonstrate the differences between statistical and deterministic deconvolution processing sequences. It will be shown, using sonic logs from wells adjacent to the seismic line, that the deterministic deconvolution sections for all three sources are close to zero phase while the statistical deconvolution sections have residual average phase errors between 180 and 270 degrees. The deterministic deconvolution sections have a high degree of correlation among themselves and to the wells adjacent to the line, while the statistical deconvolution sections correlate poorly to each other and to the wells. Synthetic seismograms and their impedance logs, and the seismic sections and their corresponding pseudo‐sonic logs, are used to demonstrate how deconvolution influences lithologic interpretation. ™Western Geophysics Co.
The attenuation of longitudinal body waves generated by local shocks in southern Peru was investigated. Thirty-four shocks, with focal depths between 20 and 180 km, were used in the study of attenuation as a function of depth and as a function of frequency (1-30 cps). Shocks were recorded on magnetic tape at three stations along the western flank of the Andes. The dimensionless specific attenuation factor Q was computed from measurements of the relative change in shape of P-particle velocity spectra with distance from the source. Near surface effects on amplitudes were taken into account. It was found that: Qp(1.5-15 cps) > 1 × 103; the attenuation of P waves increases markedly above 15 cps, probably due to scattering losses; and although absolute Qp values as a function of depth could not be resolved, an increase in P wave attenuation at a depth of about 80 km is suggested. Vp/Vs, determined from S-P and P readings at seven stations for 150 shocks, is significantly higher for oceanic shocks than inland shocks.
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