The role of fracture zones in sea floor spreading

Abstract

Considerations of the differential movement between North and South America suggest that many of the fracture zones offsetting the mid-Atlantic ridge in the equatorial Atlantic Ocean are not ridge-ridge transform faults. Instead, we show that these fracture zones are active left lateral faults to the west of the ridge crest; this left lateral movement is necessary to accommodate the differential movement between the two Americas. The Owen fracture zone in the northwest Indian Ocean and a fracture zone offsetting the Pacific-Antarctic ridge also show similar features; they show active faulting outside the ridge offset and progressive increase in offset produced by differential spreading rates. Because much strike slip faulting along fracture zones does not produce significant earthquake activity, plate boundaries cannot be defined solely on the basis of the occurrence of active earthquake zones.