earthquake (also known as a quake, tremor, temblor or seismic activity) is the result of a sudden release of energy in the Earths (Earth) crust (crust (geology)) that creates seismic waves. Earthquakes are measured with a seismometer; a device which also records is known as a seismograph. The moment magnitude (Moment magnitude scale) (or the related and mostly obsolete Richter (Richter magnitude scale) magnitude) of an earthquake is conventionally reported, with magnitude 3 or lower earthquakes being mostly imperceptible (wikt:imperceptible) and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale (Mercalli intensity scale).

At the Earths surface, earthquakes manifest themselves by shaking and sometimes displacing the ground. When a large earthquake epicenter is located offshore, the seabed sometimes suffers sufficient displacement to cause a tsunami. The shaking in earthquakes can also trigger landslides and occasionally volcanic activity.

In its most generic sense, the word earthquake is used to describe any seismic event ? whether a natural phenomenon or an event caused by humans ? that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults (Fault (geology)), but also by volcanic activity, landslides, mine blasts, and nuclear experiments. An earthquakes point of initial rupture is called its focus (focus (earthquake)) or hypocenter. The term epicenter refers to the point at ground level directly above the hypocenter.

s, 1963–1998