What is an earthquake?

An earthquake is defined as a sudden shaking or vibration of the ground, which is caused by the movement of tectonic plates along faults in the Earth's crust. When these plates shift, they can release built-up energy in the form of seismic waves, resulting in the characteristic shaking that we associate with earthquakes. This process occurs very quickly, which differentiates an earthquake from other geological phenomena that may involve slower ground movements.

The other options describe different geological processes but do not capture the essence of what constitutes an earthquake. For example, a slow movement of the ground is more representative of geological creep rather than an earthquake. A release of gases, while it may occur in some geological contexts, is not related to the seismic activity that defines an earthquake. Finally, while earthquakes can occur in relation to volcanic activity, the definition of an earthquake specifically pertains to the movements of tectonic plates, making it distinct from volcanic eruptions or related phenomena.