A fault trace describes the intersection of a geological fault with the Earth's surface, which leaves a visible disturbance on the surface, usually looking like a crack in the surface with jagged rock structures protruding outward. The term also applies to a line plotted on a geological map to represent a fault. These fractures tend to occur when a slip surface expands from a fault core, especially during an earthquake. This tends to occur with fault displacement, in which surfaces on both sides of a fault, known as fault blocks, separate horizontally or vertically.

Faults, at the broadest level, can be differentiated by the relative motion between their fault blocks.

Horizontal motion is indicative of what is known as a strike-slip fault and does not usually show much vertical separation. This is when the motion along the fault is parallel to the fault trace, usually caused by underlying plate tectonics . These fault traces are often identified by some kind of linear feature on the surface such as a fence line or small stream that has been offset. There are many photos of straight fences that suddenly jump over a meter or two leaving a gap in between. In nature, linear features are uncommon and can help identify geologic features like faults because of their linear fault traces.

Dip separation can also occur when motion of the fault is perpendicular to the fault trace. That is, the fault blocks are pulled away from each other or pushed towards each other. This is known as a dip-slip fault. This causes vertical separation between the blocks as one is dropped down in the space created by extensional forces, or one block is shoved up on top of the other by compressional forces. Again, the underlying regional plate tectonics are often responsible for the type of fault and associated trace. This vertical separation reveals a new face which had previously been buried and extends along the length of the fault trace. This new face is a specific type of fault trace known as a fault scarp.

As mentioned above, a scarp is a formation caused by vertical offset between two fault blocks. Fault scarps can be seen as meter high faces abruptly jutting out of the surface, or a small face only a few centimeters high which will be smoothed out quickly by mass wasting and erosional forces.

As a fault moves, the material both at and beneath the surface gets disturbed. These disturbances often cause different rocks and sediment, which are composed of different minerals, as well as fluids to be brought to the surface. Different minerals can contain different nutrients and elements that either enrich soils around them, or alter them in such a way that makes it more difficult for plants to grow. These changes in the soil can cause noticeable changes in the vegetation and form a fault trace.

Not only are large scale linear features indicative of fault traces but small lineations found on rock samples or rock faces also are. Slickenlines are one type of lineation which are linear gouges scraped into a rock from different rocks grinding along against each other. Slickenlines indicate a fault as well as its motion, which can be very useful in many studies.

Similar to fault scarps, and often displayed as them, elevation changes can often be good indicators of a fault. A portion of the land can be dropped down or thrust up during faulting and these can be obvious fault trace indicators, especially if seen in linear formations.