faults

A fault is a planar fracture in rock along which there has been relative movement of the blocks on either side. Faults form when rocks break under tectonic stress, typically at crustal boundaries, and they commonly appear as zones of fractured and weakened rock that can host earthquakes.

Geologic faults are classified by the direction of slip. Dip-slip faults move mainly up or down the fault plane and include normal faults (hanging wall moves downward), reverse faults, and thrust faults. Strike-slip faults move predominantly horizontally, with two blocks sliding past each other; oblique-slip faults combine these motions.

Movement on faults releases energy as earthquakes and can produce surface ruptures, mineralization, and stepped terrain. Faults can be active, with ongoing movement, or inactive and reactivated later. They often occur in fault zones with multiple parallel or intersecting faults, affecting regional seismic hazard and landscape evolution.

In engineering and industry, the term fault also refers to failures in mechanical systems, devices, or processes. Causes include wear, fatigue, misalignment, manufacturing defects, or overload. Faults degrade performance, risk sudden breakdowns, and are typically addressed through inspection, maintenance, and fault-tolerant design.

In software engineering, a fault (or defect) is an incorrect or missing line of code, design flaw, or requirement error that can cause a program to behave unexpectedly. Distinctions are made among faults, errors, and failures. Debugging, testing, and quality assurance aim to locate and remove faults, while fault tolerance adds resilience.

Across domains, recognizing faults enables assessment of risk, planning of remediation, and understanding of natural processes. While faults are natural features of the Earth, careful study and monitoring mitigate hazards and inform engineering practices.