n.
Sudden disturbance within the Earth manifested at the surface by a shaking of the ground caused by seismic wave s.
The origin and distribution of most major earthquakes can be explained in terms of fault s and the plate tectonics theory. Earthquake magnitude (a quantitative measure of amplitude and energy released) is usually expressed in terms of the Richter scale . Earthquake intensity is rated on the Mercalli scale, based on a qualitative measure (e.g., "barely felt" or "catastrophic destruction") of damage to terrain and structures at any given location. In general, a quake's intensity decreases with distance from its epicentre , but other factors, including surface geology, may significantly influence its effects. See also seismology .