Transform fault - Wikipedia
Most earthquakes occur at the boundaries where the plates meet. Earthquakes at transform faults tend to occur at shallow depths and form. Discusses the large, shallow focus earthquakes at transform plate boundaries with particular emphasis on the San Andreas Fault Zone. A smaller number of transform faults cut continental lithosphere. The most famous example of this is the San Andreas Fault Zone of western North America.
This hypothesis was confirmed in a study of the fault plane solutions that showed the slip on transform faults points in the opposite direction than classical interpretation would suggest. Both types of fault are strike-slip or side-to-side in movement; nevertheless, transform faults end at the junction of another plate boundary or fault type, while transcurrent faults die out without a junction. In addition, transform faults have equal deformation across the entire fault line, while transcurrent faults have greater displacement in the middle of the fault zone and less on the margins.
Finally, transform faults can form a tectonic plate boundary, while transcurrent faults cannot. Mechanics[ edit ] The effect of a fault is to relieve strainwhich can be caused by compressionextension, or lateral stress in the rock layers at the surface or deep in the Earth's subsurface. Transform faults specifically relieve strain by transporting the strain between ridges or subduction zones.
Transform Boundaries - Earthquakes & Plate Tectonics - Geology for Kids
They also act as the plane of weakness, which may result in splitting in rift zones. Examples[ edit ] Transform faults are commonly found linking segments of mid-oceanic ridges or spreading centres. These mid-oceanic ridges are where new seafloor is constantly created through the upwelling of new basaltic magma. With new seafloor being pushed and pulled out, the older seafloor slowly slides away from the mid-oceanic ridges toward the continents.
Although separated only by tens of kilometers, this separation between segments of the ridges causes portions of the seafloor to push past each other in opposing directions.
This lateral movement of seafloors past each other is where transform faults are currently active. Spreading center and strips Transform faults move differently from a strike-slip fault at the mid-oceanic ridge. Instead of the ridges moving away from each other, as they do in other strike-slip faults, transform-fault ridges remain in the same, fixed locations, and the new ocean seafloor created at the ridges is pushed away from the ridge.
Evidence of this motion can be found in paleomagnetic striping on the seafloor. There are two kinds of convergent boundaries: A subduction boundary is marked by the oceanic crust of one plate that is being pushed downward beneath the continental or oceanic crust of another plate. A collision boundary separates two continental plates that are pushed into contact; the suture zone is the line of collision.
Both types of boundaries have distinctive earthquake patterns.
Plate Tectonic, Volcanoes and Earthquakes
Earthquakes associated with a collision boundary define shallow, broad zones of seismic activity that form in complex fault systems along the suture zone.
Earthquake patterns in subduction zones are more complex. As the oceanic crust begins to descend, it begins to break into blocks because of tension stress. Earthquakes also periodically occur as the plate continues to subduct up to a depth of about kilometers miles.
Earthquakes are relatively abundant in the first kilometers miles of a subduction zone, are scarce from to kilometers to milesand then increase slightly again from to kilometers to miles.
Earthquakes and Plate Tectonics
It is possible that these deepest quakes are related to sudden mineral transformations and resultant energy releases or volume changes. It has been theorized that earthquakes do not occur at depths greater than kilometers because the subducting plate is not brittle anymore and has become hot enough to flow plastically.
The distribution of earthquake foci along a subduction zone gives an accurate profile of the angle of the descending plate. Most often, plates start subducting at a shallow angle, which becomes steeper with depth.