Speed Limit for Oceanic Transform Faults

Oceanic transform faults with slip rates greater than ∼145 km/m.y. do not currently exist along the East Pacific Rise where sea-floor spreading rates range from 145 to 160 km/m.y. Instead, offsets of the the very fast spreading East Pacific Rise are accommodated by microplates, propogating rifts, or overlapping spreading centers. This suggests that there might be a speed limit above which transform faults do not exist. A physical reason for a speed limit is not known, but it might be related to unstable stress fields near the rifts tips, causing them to episodically propagate and prevent a transform fault from being formed. The spreading rates quoted are from our new (0-0.73 Ma) relative-motion model for the Pacific and Nazca plates.