The two techniques used to study the gravity signature of slow-spreading give conflicting results. The admittance function technique compares observed spectra of gravity and topography with the sprecta predicted from isostatic models. This technique suggests that the topography at slow spreading ridges is supported by an elastic plate 8-10 km thick. When gravity and topography profiles are stacked, however, the admittance values increase apparently due to noise and structural variations. The residual gravity technique incrementally strips the observed gravity anomaly of its components calculated from simple assumptions of crust and mantle structure; the result is impterpreted in terms of deviations from the assumptions. This method fails to predict observed thinning of the crust near fracture zones suggesting that the method is not sensitive to crustal structure. The principal investigator will determine the limitations of the two techniques and effects of along axis structural variability and the dimensionality of the topography on the results. Both techniques will then be applies to a dense bathymetric and gravity data set between 45 and 47 N on the Mid-Atlantic Ridge. The following questions will be addressed in this analysis. (1) What is the crustal structure of the axial rift valley of a slow spreading ridge? (2) Is this crustal structure supported locally, regionally, or dynamically? (3) Are the along axis variations in axial morophology reflected in changes in the crustal structure and isostatic state?
