Transform Boundary Map

A transform boundary is where two tectonic plates slide past each other sideways, so crust is neither made nor destroyed.

Data source: PB2002 plate model, Bird (2003), converted by Hugo Ahlenius, Nordpil, ODC-By 1.0. Download: CSV .

Last updated 11 October 2026

What is a transform boundary?

At a transform boundary two plates slide past each other sideways. Crust is neither made nor destroyed, but the plates do not slide smoothly: they lock, build up strain and slip in earthquakes. USGS credits the Canadian geophysicist J. Tuzo Wilson with the idea of transform faults.

Most transform faults lie on the ocean floor, where they offset the mid-ocean ridges into a zigzag. The scars they leave, fracture zones, run on across the sea floor and can be up to 8 km deep. That is why this type has the most separate segments in the data: 751 pieces for 73,959 km.

A few cut through continents. The best known is the San Andreas Fault in California, where the Pacific Plate moves past the North American Plate. USGS describes it as about 1,300 km long, with an average motion of about 5 cm a year over the past 10 million years. PB2002 splits this type into oceanic and continental transform faults.

How the three types compare

The three plate boundary types, PB2002 totals
Type	Plates move	Crust	Length (km)	Mean speed (mm/yr)
Divergent	Apart	Made	94,840	38.2
Convergent	Together	Destroyed or crumpled	91,765	44.7
Transform	Side by side	Neither made nor destroyed	73,959	34.9

Data source: PB2002 plate model, Bird (2003), converted by Hugo Ahlenius, Nordpil, ODC-By 1.0.

Key facts

PB2002 maps 73,959 km of transform boundary, 28% of all plate boundaries. Bird (2003)
Oceanic transform faults (OTF) make up 47,825 km, with a mean speed of 40.5 mm/yr.
Continental transform faults (CTF) make up 26,134 km, with a mean speed of 24.8 mm/yr.
103 pairs of plates meet along a transform boundary. The longest shared stretch is between the African and South American plates: 6,803 km.
The fastest transform step is between the Pacific and Tonga plates near 15°S, 174°W: 263.3 mm/yr (26.3 cm/yr).

Plate pairs on transform boundaries

The plates that share the most transform boundary, by length. Speed is the relative velocity across the boundary , averaged over its length. Plate names link to their pages where we have one.

Top plate pairs by transform boundary length
Plates	Length (km)	Mean speed (mm/yr)	Classes
African and South American	6,803	31.2	OTF
Pacific and Antarctic	3,747	69.0	OTF
Australian and Antarctic	3,696	67.2	OTF
North American and Pacific	3,030	47.1	OTF, CTF
Antarctic and Nazca	2,663	56.9	OTF
Caribbean and North American	2,482	16.9	OTF, CTF
Somali and Antarctic	2,251	11.6	OTF
North American and Eurasian	2,079	16.0	CTF, OTF
Somali and African	2,059	2.5	CTF, OTF
Amur and Eurasian	1,927	9.9	CTF
African and Antarctic	1,826	13.7	OTF
Scotia and South American	1,795	4.4	OTF, CTF

Data source: PB2002 plate model, Bird (2003), converted by Hugo Ahlenius, Nordpil, ODC-By 1.0.

Longest transform segments

A segment here is one unbroken run of the same boundary class between the same two plates. The location is the middle of the run.

Longest continuous transform segments
Plates	Class	Length (km)	Mean speed (mm/yr)	Near
Amur and Eurasian	CTF	1,320	10.0	56°N, 129°E
Antarctic and Nazca	OTF	1,037	56.3	36°S, 104°W
Anatolia and Eurasian	CTF	923	24.3	41°N, 36°E
African and South American	OTF	916	31.1	0°S, 20°W
Okhotsk and North American	CTF	901	3.1	61°N, 162°E
Scotia and South American	CTF	767	4.5	54°S, 72°W
North American and Pacific	CTF	752	45.9	37°N, 122°W
Pacific and Caroline	OTF	699	11.5	8°N, 142°E
Indian and Eurasian	CTF	697	52.9	25°N, 96°E
Australian and Maoke	CTF	660	12.8	4°S, 138°E

Data source: PB2002 plate model, Bird (2003), converted by Hugo Ahlenius, Nordpil, ODC-By 1.0.

Speeds range from 0.3 mm/yr to 263.3 mm/yr along this type. For every boundary in one view see the plate boundaries map, compare with the other types: divergent and convergent , or see how fast plates move on the plate motion map. All plates are on the tectonic plates map.

Print this map Plate boundaries worksheet. Label each boundary type, with an answer key

Glossary

Transform boundary: Plates slide horizontally past each other. Crust is neither made nor destroyed. Source
Mid-ocean ridge: An underwater mountain range that forms along divergent plate boundaries, where new ocean floor is made. Source
Relative plate velocity: How fast one plate moves compared with its neighbor across a boundary, in millimeters per year. Source

All terms in the glossary

Transform boundary FAQ

What happens at a transform boundary?

Two plates slide past each other horizontally. Crust is neither made nor destroyed, but the plates lock and slip, which causes earthquakes.

What is the best-known transform boundary?

The San Andreas Fault in California, where the Pacific Plate slides past the North American Plate. USGS describes it as about 1,300 km long, with an average motion of about 5 cm a year over the past 10 million years.

Where are most transform faults?

On the ocean floor. They cut the mid-ocean ridges into offset pieces, which is why the ridges look like a zigzag on the map.

Who discovered transform faults?

The Canadian geophysicist J. Tuzo Wilson proposed them, according to USGS.

How many transform segments does PB2002 have?

751 separate segments with 73,959 km in total, the most segments of any type even though they are often short.

Sources: USGS, Understanding plate motions; Bird (2003) for all lengths and speeds.