A transform fault is a plate boundary where two plates slide sideways past each other. No crust is made or destroyed there. On the ocean floor, transform faults cut across mid-ocean ridges and shift them sideways, giving ridges a zig-zag shape.
Key takeaways
- At a transform boundary, crust is neither produced nor destroyed as the plates slide horizontally past each other [1].
- Most transform faults are on the ocean floor, where they offset the active spreading ridges and make zig-zag plate margins [1].
- The San Andreas fault in California is one of the few transform faults exposed on land [1].
- Our map lists 29 named fracture zones, the long scars that transform faults leave across the seafloor.
How a transform fault works
There are four kinds of plate boundary. At a divergent boundary, plates pull apart and new crust is made. At a convergent boundary, one plate dives under another and crust is destroyed. At a transform boundary, the plates simply slide horizontally past each other, and crust is neither produced nor destroyed [1].
The idea came from the Canadian geophysicist J. Tuzo Wilson, who proposed that large faults connect two spreading centres or, less often, two trenches [1].
On the ocean floor, mid-ocean ridges are not continuous straight lines. They are broken into segments that are shifted sideways, one from the next. Transform faults run between those offset segments. The result is a zig-zag pattern, like a staircase seen from above [1]. This happens because the spreading does not always point straight at right angles to the overall line of the ridge [2].
The active part of a transform fault is short. It stretches only between the two ridge crests it connects. Beyond them, the plates on either side are moving in the same direction, so the fault stops being a plate boundary. What remains is a long, mostly quiet scar called a fracture zone, which can run for hundreds or thousands of kilometres across the older ocean floor [1].
Transform faults are not only underwater. USGS points to the San Andreas fault zone in California, about 1,300 kilometres long, as one of the few transform faults exposed on land, where the Pacific Plate grinds past the North American Plate at about 5 centimetres a year [1].
An example from our data
Our map does not draw plate boundaries or fault lines, so it cannot show you a transform fault directly. What it does show is the seabed shape they leave behind, and it names the largest scars.
The Charlie-Gibbs Fracture Zone cuts across the Mid-Atlantic Ridge in the North Atlantic. At its listed point the GEBCO grid reads 4,013 m, about 1,420 km from Portugal. The Walton fault zone is listed at 4,603 m, near Jamaica.
In all, our list has 29 named fracture zones, out of 950 named undersea features. To spot them yourself, zoom out on the map and look for narrow lines that run at right angles across a ridge.
The thing people get wrong
People often assume a transform fault is where new seafloor is made, or where it is destroyed. It is neither. The fault is a sliding boundary, so the plates move past each other without gaining or losing crust there. The new crust is made at the ridge segments at each end, and the old crust is destroyed far away at subduction zones.
Another common mistake is to treat the whole line you see on a bathymetric map as the plate boundary. Only the section between the ridge segments is. The extension past them is a fracture zone, which is not a boundary at all, because the crust on both sides belongs to the same plate [3].
Transform fault vs fracture zone
Frequently asked questions
What is the difference between a transform fault and a fracture zone?
A transform fault is the active part, between two offset ridge segments, where plates slide past each other. A fracture zone is the longer, mostly inactive scar that continues beyond it.
Do transform faults cause earthquakes?
Yes. They are generally defined by shallow earthquakes, because the plates grind past each other rather than moving smoothly.
Sources
- Understanding plate motions, USGS (This Dynamic Earth).
- Transform fault, Wikipedia.
- Fracture zone, Wikipedia.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against GEBCO_2026 grid).