The data of the Seamat Cruise indicate that: a) the junction between the East Pacific Rise and the Rivera Fracture Zone is located 165 km seaward the Acapulco Trench axis at 18 degree 30'N latitude and 106 degree 15'W longitude; and b) the East Pacific Rise axial ridge connects the Rivera Transverse Ridge trough an overshot ridge. This situation makes the Rivera Fracture Zone located eastward of the junction progressively inactive and documents a westward jump of the junction.