Plate Tectonics

Transform Plate Boundaries

At transform fault boundaries, plates slide past one another; no new lithosphere is created or destroyed. Most join two segments of a mid-ocean ridge as parts of prominent linear breaks in the oceanic crust known as fracture zones. There are two types of transform faults:

• Oceanic - located entirely in the ocean
• Continental - located entirely on the continent

Image source:  "Fig 25" by USGS is in thePublic Domain

There are two parts of the fault: the active and the inactive portions. The active portion is between the two ridge axes, where one side is moving in the opposite direction from the other. The inactive portion is on the outside of the ridge axes, where the two sides are moving in the same direction but at different speeds. The fault will continue to propagate until both sides are moving at the same speed.

Image source: "Google Maps Satelite Imagery" Google Earth by is in the Public Domain , with annotations by  Sonjia Leyva © 2020.
 

Below are two videos on transform faults.  In the first, I explain the difference between a transform fault and a fracture zone.  In the second, "Transform Fault—San Andreas" by IRIS Earthquake Science.   As you watch both, note the following:

• There is no audio!
• Is the San Andreas Fault a transform, or a fracture zone?  How can you tell?
• If the San Andres is an "uncommon" fault because it is on land, where do you think all the other transform faults/fracture zones are located?

Video #1:  Transform fault vs. Fracture zone - What's the difference?

Video #2:  Transform Fault - San Andreas