Earthquakes

An earthquake is a sudden shaking of the ground caused by the rapid release of energy inside the Earth. Most earthquakes occur when tectonic plates, the large rocky slabs that make up the Earth's outer shell, move along faults. As stress builds over time, the rocks eventually break or slip, sending seismic waves through the ground.

The point where the rupture begins is called the focus, while the point directly above it on the surface is the epicenter. Earthquakes vary greatly in strength. Many are so small that only sensitive instruments called seismometers can detect them, while the strongest can damage buildings, roads and other infrastructure over large areas.

Scientists describe an earthquake's size by its magnitude, which measures the energy released, and its intensity, which describes the effects felt at different locations. Large earthquakes are often followed by aftershocks as the rocks continue to adjust. In some cases, especially beneath the ocean, a powerful earthquake can trigger a tsunami.

Although earthquakes cannot currently be predicted precisely, scientists monitor seismic activity, map active faults and study plate movements to better understand where they are likely to occur. Earthquake-resistant construction, early warning systems in some regions and public preparedness all help reduce the risks and protect lives.