faulting

Faulting is the fracturing of rocks and the displacement that follows when tectonic stresses exceed the strength of rocks in the Earth's crust. It is a key mechanism by which crustal blocks accommodate movement between tectonic plates. Faulting is typically brittle and occurs in the upper to mid-crust, producing surface ruptures, fault traces, and zones of fractured rock.

The main families of faults are defined by slip direction. Normal faults occur in extensional settings, with the hanging wall moving downward relative to the footwall. Reverse faults, including thrust faults, form under compression, with the hanging wall moving up or over the footwall. Strike-slip faults involve predominantly horizontal motion, as the blocks slide past one another; oblique faults combine components of both vertical and horizontal movement.

A fault is characterized by a fault plane along which displacement occurs, and by related features such as fault gouge, fractured rocks, and the surrounding fault zone. Surface rupture can accompany earthquakes, while some faults exhibit slow, aseismic creep. Faulting often interacts with folding and other deformation processes to shape landscapes, mountain belts, basins, and fault scarps.

Formation and activity are controlled by plate tectonics and regional stress fields. Faults concentrate deformation along plate boundaries and within plates, and their activity is a major source of seismic hazard. Monitoring and study—through geological trenching, seismology, GPS, and InSAR—help determine fault locations, slip rates, and potential earthquake risk for nearby populations and infrastructure.