Sonar studies of the Mid-Atlantic Ridge and Kurchatov Fracture Zone

Abstract

A survey of the Mid-Atlantic Ridge crest in the region of the Kurchatov Fracture Zone (40.5°N) employing a long-range side-scan sonar is described. Away from the fracture zone, long straight faults spaced about 2 km apart and parallel to the ridge axis were seen. Almost all of these faults seem to be generated on the median valley floor within a few kilometers of the axis. The inferred heights of the fault scarps are consistent with the fact that most of the uplift in the median valley walls is accommodated on inward facing normal faults of a few hundred meters' throw. The mean height of inward facing fault scarps decreases only slightly outside the median valley, an indication that reverse movements on these faults are not significant processes. The active section of the fracture zone is characterized by a deep trough of 055° trend, which it is believed represents an oblique spreading center. There is no indication of the presence of a transform fault. Oblique faults seen within the fracture zone were probably produced by repeated shearing and healing of the sea floor within the active section and may themselves control the trend of the oblique spreading center. Subsequent vertical movements along some of these oblique faults have produced spectacular serrated walls for the fracture zone valley. The persistence of the fracture zone topography requires that the two sides of the fracture become welded together after leaving the active section.