Dereverberation of marine reflection seismic data by a spatial combination of predictive deconvolution and velocity filtering

Abstract

Abstract. Contamination of seismic reflection records at early times by first-order water reverberations can be especially severe during survey operations over hard and flat sea floors on the continental shelf or in lake environments. A new dereverberation scheme based on two classical techniques -predictive deconvolution and velocity filtering -has been developed to address this problem. The techniques are combined spatially to take advantage of their complementary offset-and time-dependent properties. Stage I of the scheme consists of applying predictive deconvolution at short offset. The data are previously conditioned by a normal moveout correction with the water velocity which restores the periodicity of the reverberations in the offset-time plane and enhances the performance ofdeconvolution. Stage II of the scheme involves velocity filtering in the common-midpoint domain which is particularly effective at long offset where the moveout difference between primary reflections and reverberations is largest. The dereverberation scheme is well suited for the initial processing of large volumes of data due to the general availability of costeffective deconvolution and velocity filtering algorithms in seismic processing software packages. Practical implementation issues are illustrated by a field example from the GLIMPCE survey in Lake Superior. Statement of ProblemThe generation of first-order water reverberations during marine reflection seismic operations is illustrated in Figure 1 a using a basic near-surface model comprising a water layer of constant thickness z and velocity vw overlying a half-space rock substratum of velocity v > v~. As a result of the large impedance contrasts at both the air-water and water-rock interfaces, energy is trapped in the water layer which gives rise to a long oscillatory wavetrain on each seismic trace. The two-way travel time curve tn(x) of the nth water reflection is a hyperbola in the shot and common-midpoint (CMP) domains:( 1) whereand x is the source-receiver offset and T the reverberation period at zero offset. The travel time curves of the primary water bottom reflection (n = 1) and of the first four water reverberations (2 _< n _< 5) are shown schematically in Figure lb (solid lines) for a hypothetical shot or CMP gather. In a more realistic multi-layered earth model, the first-order water reverberation wavetrain would mask primary reflections at early times. The goal of water dereverberation is thus to suppress events corresponding to n _> 2. There exists a wealth of techniques for the suppression of multiple energy of which water dereverberation is a more specialized problem. They can be classified into two main categories according to the criterion used to distinguish multiples from primary reflections: (1) moveout difference and (2) predictibility.The simplest multiple suppression operation based on the first criterion is the general stacking operation itself. The most commonly used specialized technique is velocity filtering (Embree et at., 1963), which can be used ...

Processing and modelling of short-offset seismic refraction-coincident deep seismic reflection data sets in sedimentary basins: an approach for exploring the underlying deep crustal structures

“…It is clear that velocity filtering is quite a common procedure routinely applied to multichannel seismic data, both in the narrow‐angle and WA experiments for shallow and deep crustal studies (e.g. Klemperer 1989; Samson & West 1992, 1995; Minshull 1993). We utilize here this processing with advantage especially for attenuating the multiples, thereby developing the weak SC reflections from the deep crust for the first time.…”