Geoenvironmental characterization of selected shallow-water sites on the western European continental shelf (SWAP)

Abstract

Geoenvironrnental analyses for four experiment sites on the continental

shelf to the west of Britain and the English Channel have utilized two modes of shallow reflection seismic profiling, side-scan sonar, and bottom and sub-bottom sampling to derive environmental information relevant to predicting bottom-acoustic interaction. Because of the geological development of the

shelf and the history of sea-level rise and fall over the past 1,000,000 years, and especially over the last 15,000 years, solid rock and sediment materials having very different physical properties and frequency-dependent acoustic response

are located at or very close to the sea bottom. Recent sediment is very thin to absent both on the inner and outer shelves, and features characterized as being products of recent sedimentation will respond, at higher frequencies, as solid rock materials. Bottom-acoustic interaction, therefore, is strongly dependent on the type of rock and sediment material in tlie bottom at any particular place. These have been grouped into a number of geoacoustic terranes, based on their physical properties and some transmission loss data from eiulier

acoustic experiments, which could be related to individual bottom materials. Acoustic response for individual materials can be expected to remain constant everywhere on this shelf, and thus characterization of response, at a number of selected sites through acoustic experiments, can theoretically be used to predict general response elsewhere where geologic conditions ilre similar.