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How do geologists distinguish a fault from a joint?
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geology
A rock formation called “faux amphibolite,” from the Nuvvuagittuq greenstone belt in northern Quebec, dated to 4.28 billion years ago.
In structural geology, geologists distinguish between a fault and a joint primarily based on whether displacement has occurred along the fracture surface.1
- Faults: These are fractures in the Earth's crust where the rocks on opposite sides have moved in opposite directions relative to one another. This displacement can range from less than a centimetre to hundreds of kilometres.21
- Joints: These are brittle-fracture surfaces in rocks along which little or no displacement has occurred.31
Both features are considered secondary structures, meaning they form after the rock itself has been created, typically as a result of crustal movement, contraction during cooling, or weathering processes. While faults are often associated with significant tectonic activity and earthquakes, joints are ubiquitous in surface rocks and are frequently found in systematic sets.312