ELSEVIER Tectonophysics 264 (1996) 357-370 TECTONOPHYSICS Relative-amplitude preserving processing for crustal seismic reflection data: an example from western Canada David W.S. Eaton *, Jianjun Wu Geological Survey of Canada, 1 Observatory Crescent, Ottawa K1A OY3, Canada Received 8 March 1995; accepted 30 November 1995 Abstract Most crustal-scale seismic reflection profiles are processed using methods that preserve reflection geometries but not true-relative amplitudes, and therefore do not provide direct constraints on the magnitude of impedance contrasts at major crustal boundaries, the effects of attenuation in the crust or the maximum time of signal penetration. Here we describe a new relative-amplitude preserving (RAP) processing scheme tailored for high-fold, land-based acquisition systems that can be used to provide some of these constraints. Our processing philosophy employs a statistical treatment of amplitudes, and is based on the following assumptions: (1) temporal decay of recorded amplitudes is proportional to the product of zero-offset geometrical spreading in a layered earth and attenuation based on a constant-Q model; and, (2) spatial variations in recorded amplitudes are surface-consistent. We apply this methodology to a profile from western Canada, where well logs from oil and gas exploration are available to calibrate observed seismic reflections. Using a spectral-ratio method tailored for noisy data, we obtain an estimate of ~ 450 for apparent Q in the sub-Phanerozoic crust. Signal penetration is frequency-dependent, and is estimated to decrease from 20 to 13 s over the frequency range of 10 to 40 Hz. Application of our processing methodology leads to a stack section in which lower-crustal reflectivity is much more prominent than reflectivity in the middle crust, compared with conventional processing of the same data which yields a stack section characterized by conspicuous mid-crustal reflections. The P-wave reflection coefficient for the Moho is estimated to be about 0.1. Keywords: seismic profiles; data processing; attenuation; Mohorovicic discontinuity 1. Introduction The goal of seismic-reflection processing is to render an image from the recorded wavefield that accurately depicts the true structural configuration of reflectors in the subsurface. For crustal-scale pro- files, many common processing steps (e.g., automatic gain control or AGC) do not preserve true-relative amplitudes in the data. Thus, potentially important * Corresponding author. Fax: 613 992-8836. information concerning the state and composition of the lithosphere, such as impedance changes at major boundaries or quality factor (Q), become unavailable to the interpreter. To address this shortcoming, so-called true-am- plitude processing techniques have been used in- creasingly to support the interpretation of crustal profiles. For example, Mayrand and Milkereit (1988) combined true-amplitude processing with algorithms for automatic trace editing and noise rejection to study reflective zones imaged by Lithoprobe Vibro- 0040-1951/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PII S0040- 1 951 (96)00 136-9