3-D high‐resolution reflection seismic imaging of unconsolidated glacial and glaciolacustrine sediments: processing and interpretation

Abstract

Shallow 3-D seismic reflection techniques have been used to map glacial deposits in a Swiss mountain valley. A dense distribution of source and receiver positions resulted in a small subsurface sampling of 1.5 m × 1.5 m and a high fold of >40. Common processing operations that included pseudotrue amplitude scaling, deconvolution, and band‐pass filtering successfully enhanced shallow reflections relative to source‐generated noise. Careful top muting helped avoid erroneous stacking of direct and guided waves. Azimuth‐dependent velocity analyses proved to be unnecessary. Three‐dimensional (3-D) migration of the stacked data yielded the final high‐resolution images of the shallow subsurface (15–170 m). Because most reflections and diffractions were migrated to their correct subsurface locations, confident interpretations of 3-D structures were possible. Time slices and cross‐sections along arbitrary directions proved to be powerful analysis tools. Even small‐scale features (<20 m wide), such as subglacial channels and troughs, could be mapped. Five major lithologic units separated by four principal reflecting boundaries were distinguished on the basis of their characteristic seismic facies. The principal reflecting boundaries were semiautomatically tracked through the 3-D data volume. Borehole information allowed the uppermost boundary at 15–27 m to be identified as the top of a 68–80-m-thick sequence of basal and reworked tills characterized by high‐amplitude discontinuous to quasi‐continuous reflections. Low reflectivity of seismic units above and below the till units was associated with finely layered or massive glaciolacustrine clay/silt deposited during and after two principal phases of glaciation (Würm at 28 000 to 10 000 and Riss at 200 000 to 100 000 years before the present). Top of Tertiary Molasse basement was delineated by prominent east‐dipping reflections at variable depths of 85–170 m.

High-resolution seismic sub-bottom reflection record of low hypsithermal lake levels in Ontario lakes

“…6-10 and comprise the primary database for this paper. Sub-bottom geophysical data from lakes can be analyzed using the same conventional sequence stratigraphic analysis methods widely used in marine basins (e.g., Buker et al, 2000). In this way, prominent subsurface horizons such as sequence boundaries are hand "picked" and traced along profiles which allows the sub-bottom stratigraphy to be subdivided into several "seismosequences" characterised by different seismic reflection properties and lower and upper bounding surfaces which in turn, reflect sediment type and thus the depositional history of each basin.…”

Portable dense geophone array for shallow and very shallow 3D seismic reflection surveying: Part 1—Data acquisition, quality control, and processing

“…Examples of three-dimensional shallow seismic reflection on land have been reported since the late 1980s (Buker et al, 1998). Lanz et al (1996) point out that 3D seismic imaging collapses out-of-plane reflections and improves 2D seismic interpretation.…”

“…Lanz et al (1996) point out that 3D seismic imaging collapses out-of-plane reflections and improves 2D seismic interpretation. In two papers, Buker et al (1998Buker et al ( , 2000 show that a very-high-quality 3D shallow seismic cube can be obtained when subsurface coverage is very high. However, the dense spatial coverage increases the cost of 3D shallow seismic surveys.…”

“…However, the dense spatial coverage increases the cost of 3D shallow seismic surveys. Buker et al (1998) note that 85 days and a crew of five to eight people were required to obtain a 432 × 357-m 3D high-resolution reflection cube. Thus, based on a cost benefit analysis, it is unlikely that such 3D seismic surveys will be conducted on projects with a limited budget.…”

Application of ground penetrating radar imaging to deepwater (turbidite) outcrops

“…This information is unattainable from surface mapping, which only rarely can map exterior structure and never can access the interior of a volume. Widespread use of 3D GPR surveys in recent years has resulted in detailed pictures of the spatial geometry of reflectors (Buker, Green, & Horstmeyer, 2000;Young & Sun, 1996), characterization of clastic reservoir outcrop analogs (Corbeanu, et al, 2002), and determination of petrophysical properties for use in building reservoir flow simulation models . GPR data is also sub-seismic in resolution and therefore captures significant structural and sedimentary features at a scale that would be missed even by an extensive distribution of boreholes.…”