Short answer
A fracture is a break in rock. A fault is a fracture, or zone of fractures, across which rock blocks have moved relative to one another. The key evidence is displacement, not just the presence of a crack. 1 2
Every fault involves a break, but a fracture without displacement is not necessarily a fault.
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At a glance
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| Question | Fault | Fracture |
|---|---|---|
| Rock broken? | Yes | Yes |
| Relative movement? | Yes | Not required |
| Typical context | Slip and earthquakes | Broad structural description |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Fault. A fracture or fracture zone in rock across which blocks have moved relative to one another. 1
Fracture. A break or crack in rock, whether or not displacement has occurred across it. 2
Key differences
USGS defines a fault by movement across a fracture zone. Movement may happen suddenly during an earthquake or slowly by creep. A crack visible in an outcrop may be a joint or another fracture if no offset has occurred. 1 2
How to tell them apart
Look for matching rock layers or markers displaced across a break; that supports a fault. A crack with no detectable offset may be a fracture only. In the field, hidden or very small movement can make the classification uncertain. 1 2
Where they overlap
Both terms describe discontinuities in rock and may refer to the same structure. Faults often comprise multiple fractures rather than one perfectly planar split. 1 2
Edge cases
A fault may be inactive for a long time but remains a fault because displacement occurred. An absence of visible offset at one exposure does not prove that a fracture has never slipped elsewhere. 1 2
Why the distinction exists
Geologists separate broken rock from broken-and-displaced rock because displacement records deformation and affects earthquake hazards. 1 2
Common misconceptions
A fault is not simply a large crack. Size alone does not establish a fault; evidence of relative motion does. 1 2
Examples
A hairline crack through a rock with aligned layers is a fracture. If a bed is shifted across the crack, the structure is a fault. 1 2
Sources
Sources checked October 3, 2026.
- USGS — What Is a Fault?. Definition and types.
- USGS — The Science of Earthquakes. Hypocenter and epicenter.