A field program will use Seabeam and SEAMARC II simultaneously for investigating the section of the East Pacific Rise along the Pacific-Antarctic plate boundary. A principal objective is to determine how the characteristic structure of normal and oblique fracture zones are created at offsets of the rise-crest. The northern part of the Pacific-Antarctic plate boundary is well suited for such a study, because it is the best modern, active analog to the Tertiary Pacific-Kula and Pacific-Farallon spreading centers, where the well known North Pacific fracture zones were created. Sparse magnetic data from the rise flanks and the obliquity of the overall trend of the ridge crest to the spreading-normal direction suggest that it has small, migrating nontransform offsets, as well as a set of typical transform faults. Another aim of the proposed cruise is to establish the style of plan and profile segmentation of this poorly known accreting boundary.
