This project analyzes existing sonic log data from bore holes in the ocean floor to obtain high resolution velocity and attenuation estimates from which to infer the degree of fracturing in ocean crust. This is important because fluid flow in the crust is controlled primarily by fractures: in young ocean crust data indicate that the shallow crust contains many open fractures which constitute an underpressured aquifer of high permeability. With time alteration products seal these fractures which reduces the permeability and fluid flow dramatically. By integrating improved velocity data and new attenuation estimates with borehole televiewer and gamma ray logs, fractured intervals will be located and characterized as open or sealed. Variations in the nature of the alteration material in the sealed fractures will be indentified from velocity and attenuation data in conjunction with other log data and core geochemical results. Variations in the aperture or permeability of the open fractures will be identified from the attenuation data.
