Local axial migration and spreading rate variations,East Pacific Rise, 31°S

Mapping and analysis of marine magnetic anomalies generated during the past 3.78 m.y. at the East Pacific Rise crest near 31°S reveals a history of ongoing small-scale migration of the spreading center. The axis first became curved and then broke when the curvature became too severe, forming a 10-km offset. The offset healed rapidly and the topographic axis of the rise is now continuous and essentially linear. Sea-floor spreading has occurred asymmetrically in this area with east and west flank rates of 86 and 77 mm/yr, respectively, since 2.41 m.y. ago. Total spreading rates show an overall decline from 176 to 145 mm/yr prior to the Jaramillo event, 0.9 m.y. ago. For the last 0.7 m.y. the total spreading rate has been 162 mm/yr.