How Do Earthquakes Occur?

Earthquakes occur due to the sudden release of stored energy in Earth’s crust, primarily caused by tectonic movements. Earth’s crust is divided into several large and small tectonic plates that float on the semi-fluid asthenosphere beneath them. These plates are constantly moving, albeit very slowly, due to the convective currents in the mantle. When these plates interact at their boundaries, they can either collide, pull apart, or slide past each other. This interaction often occurs along faults, which are fractures in Earth’s crust where the plates have moved relative to each other. The stress and strain that build up at these fault lines can eventually exceed the strength of the rocks, causing them to fracture and slip, releasing energy in the form of seismic waves.

The elastic rebound theory provides a detailed explanation of how earthquakes occur. According to the theory, a tectonic earthquake occurs when strains in rock masses have accumulated to a point where the resulting stresses exceed the strength of the rocks, causing sudden fracturing and the release of stored energy. This sudden release of energy causes the rocks to “rebound” to a position of less strain, generating seismic waves that propagate through Earth, causing the ground to shake.

Earthquakes produce four main types of seismic waves: two types, called body waves, move through the Earth’s interior, while the other two, known as surface waves, travel along the planet’s surface. The shaking felt during an earthquake is primarily due to these seismic waves. The intensity and duration of the shaking vary across the geographic area around the epicenter of an earthquake and depend on the amount of energy released, the distance from the epicenter, and the geological characteristics of the area.