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Fracture Zone Definition and Characteristics
Fracture zones are an underwater geological feature found on ocean floors. They consist of long, narrow lines separating different levels of elevation underwater. These elevations may differ by as much as 1.5 kilometers (0.9 miles). Hence, the boundaries of fracture zones frequently consist of deep canyons. Due to geologic activity, the sea floor on one side of a fracture zone is younger in age than the floor on the opposite side. Fracture zones are not themselves tectonic plate boundaries, however; the rock on both sides of a fracture zone lies on the same plate.
Relationship to Mid-Ocean Ridges
Fracture zones often slice across mid-ocean ridges -- submarine mountains -- and can extend for several hundred kilometers beyond these ridges. Mid-ocean ridges are geologically active regions in which the sea floor is spreading in opposite directions, which means that earthquakes are common occurrences. However, these earthquakes are generally weak and shallow.
Association with Transform Faults
A type of fault known as a transform fault is found in portions of fracture zones. This type of fault involves two tectonic plates sliding past each other. This movement causes earthquakes. Fracture zones can sometimes involve complex swarms of faults -- and hence, swarms of earthquakes. Transform faults can also exist on land, but in these instances they aren't referred to as fracture zones; the San Andreas system is one such example.
Fracture Zone Not Required
Fracture zones are not the only places earthquakes occur. Earthquakes occur all over the world, on land as well as underwater, at tectonic plate boundaries as well as along faults. Most earthquakes tend to take place where at least two plates -- large pieces of the Earth̵7;s crust -- intersect. However, quakes occasionally occur far from plate borders, deep within the interiors of large continents. Hence, the occurrence of an earthquake does not necessarily imply the presence of a fracture zone.