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An illustration of the difference between the active transform faults between offset ridge axes, and inactive fracture zones.

A fracture zone is a linear oceanic feature--often hundreds, even thousands of kilometers long--resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on either side of an active transform fault move in opposite directions; here, strike-slip activity occurs. Fracture zones extend past the transform faults, away from the ridge axis; seismically inactive (because both plate segments are moving in the same direction), they display evidence of past transform fault activity, primarily in the different ages of the crust on opposite sides of the zone.

In actual usage, many transform faults aligned with fracture zones are often loosely referred to as "fracture zones" although technically, they are not.

Structure and Formation of Fracture Zones

This diagram illustrates the structure of a mid-ocean ridge before (1) and after (2) the formation of a transform fault. In (1), seafloor spreading has begun, and a mid-ocean ridge is formed. In (2), a transform fault has formed along the mid-ocean ridge, forming fracture zones on either side of the ridge.

Examples of fracture zones

See: List of fracture zones

U.S.G.S. Blanco Fracture Zone regions image

References

• U.S. Geological Survey: Understanding plate motions
• NOAA, National Geophysical Data Center & World Data Center A for Marine Geology & Geophysics (See: The Fracture Zones)