earthquake

An earthquake is the shaking of the surface caused by the abrupt release of energy in the lithosphere. This energy release creates seismic waves that propagate through Earth's interior and along its surface. Most earthquakes are caused by the movement of tectonic plates and their interactions at faults. The leading theory is elastic rebound: rocks deform under stress until they rupture and snap back to a lower energy state, producing ground shaking.

Earthquakes are classified by origin: tectonic earthquakes, the most common, created by plate interactions; volcanic earthquakes associated with magma movement; collapse earthquakes caused by underground caverns collapsing; and explosions such as mining or nuclear tests. The location of the earthquake is defined by the focus, the point within Earth where the quake starts, and the epicenter, the point at the surface directly above it. The shaking is transmitted by seismic waves: P-waves (compressional), S-waves (shear), and surface waves, with varying speeds and destructiveness.

Magnitude measures the energy released; most widely used is moment magnitude Mw. Intensity measures the observed effects at a location on the Mercalli scale. Earthquakes are most common at plate boundaries, such as the Pacific Ring of Fire, but can occur within plates as intraplate earthquakes. Hazards include ground shaking, tsunamis for offshore events, landslides, liquefaction, and fires.

Seismic monitoring networks detect and locate earthquakes with seismographs. The data support hazard assessment, early warning systems, and research. Mitigation focuses on building codes designed to strengthen structures, retrofitting vulnerable buildings, land-use planning, and public education. Preparedness aims to reduce casualties and accelerate recovery.