What is a fault line?

A fault line is a break or fracture in the Earth's crust, along which masses of rock have been displaced. They typically occur at the boundaries of tectonic plates, where the plates are shifting or grinding against each other.

Faults can vary in size from small, barely visible cracks to large, deep fractures that extend for hundreds of kilometers. Fault lines can be classified by their motion, such as strike-slip, where the two sides move horizontally past each other, or dip-slip, where the two sides move vertically up or down relative to each other.

The movement of a fault can cause earthquakes, as the sudden release of accumulated energy along the fault line sends seismic waves rippling through the Earth. Faults can also create mountains, valleys, and other major features of the Earth's landscape.