Morphological and Geophysical Investigation of Western North Atlantic Ocean Crustal Structure: Environmental Work in Support of the Acoustic Reverbation Special Research Program and Morphological and Geophysical Investigation of Western North Atlantic Ocean Crustal Structure and Fine-Scale Near-Bottom Geological and Geophysical Studies of Ocean Crust in the ONR-ARSRP Acoustic Reverbation Corridor.

The Acoustic Reverberation Special Research Program required detailed knowledge of large and small scale seafloor roughness, crustal structure, sediment distribution patterns, and material properties of the ocean floor on the MidAtlantic Ridge in order to advance fundamental research on acoustic wave scattering from the ocean bottom and subbottom at low frequencies and over long propagation paths. To provide this information and to improve our understanding of the fundamental geological processes that control formation and evolution of ocean crust and deposition of the overlying sediments, we conducted two geologicalgeophysical surveys in the Acoustic Reverberation Corridor within the ONR Atlantic Natural Laboratory at 25 deg 25 to 27 deg 10N, 45 deg 00 to 49 deg 00W. The initial survey acquired regional geological and geophysics data, and the second survey acquired fine scale, near bottom data at four seafloor sites identified by ARSRP researchers as prime acoustic study areas. This report summarizes the results of our geological and geophysical research on ridge flank tectonic segmentation the structure, roughness, composition, thickness and magnetization of the ocean crust gravity anomalies sediment distribution fault patterns and fault scarp denudation and seamount construction and degradation.