Seabed II: High-resolution Acoustic Seabed Surveys of the Deep Ocean

Abstract

Recent developments in seabed survey technology for the deep ocean have utilized a tethered deep tow vehicle with side-scan sonar, high-resolution seismic reflection profiler, motion and position sensing and real-time digital processing of data for regional and site-specific geological mapping. Among the major design considerations were the bandwidth and penetration of the profiler system; the range of the side-scan sonar; the system’s accuracy of position and attitude measurements; towed body stability; and ease of deployment and recovery. The 1000 J boomer sound source, operating at a depth of 2000 m, provided over 150 m of penetration through upper continental slope sediments with a resolution of 2 m, prior to deconvolution processing. This represents a major advance in resolution and penetration over the performance of conventional single-channel airgun and sparker seismic reflection systems and 3.5 kHz profilers.

A geological interpretation of data collected in the summer of 1984 demonstrates the system’s capabilities. The continental slope east of Sable Island, adjacent to the Scotian Shelf, is underlain by a thick sequence of glacial and post-glacial sediments extending to water depths greater than 2000 m. From 200 to 640 m water depth the seabed is covered with relict iceberg furrows. Extending from 500 to 1100 m water depth, a large field of pockmarks (gas escape craters) occurs. Locally, slumped zones indicate recent instabilities that could affect present and planned hydrocarbon drilling activity.