An earthquake (also known as a quake or tremor) is the shaking of the surface of the Earth which has resulted from a sudden release of energy in the Earth's lithosphere that creates seismic waves.
The ground starts to quiver, glasses rattle. Telltale signs of what could be a devastating earthquake. The stronger and shallower the quake, the more violent the destruction.
Earthquakes can range in intensity, from those that are so weak that they cannot be felt, to those violent enough to propel objects and people into the air and wreak destruction across entire cities.
The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time period.
Watch the video to understand how earthquake work.
Source : National Geographic