9615204 Scheirer Gravity, magnetic, side-scan sonar, and bathymetric data will be collected on the east flank of the East Pacific Rise between 15 and 20 degrees south. This region has four anomalous features: gravity lineations, abundant seamounts, asymmetric subsidence, and asymmetric spreading. the primary questions: are whether there are gravity lineations on the Nazca plate, does small-scale convection in the Pacific asthenosphere bring about the anomalous low subsidence of young Pacific seafloor, are the seamounts symmetrically distributed about the axis, and how is the long- wavelength segmentation of the ridge axis expressed off axis.