A seismic event is a natural phenomenon that involves the shaking of the Earth's surface. The most common seismic events are earthquakes, tsunamis, aftershocks, tremors, and temblors. An earthquake, also known as a QUAKE, is a sudden and violent shaking of the ground caused by the release of energy from the Earth's crust. A TSUNAMI is a large ocean wave caused by an underwater earthquake or volcanic eruption. An AFTERSHOCK is a smaller earthquake that follows the main shock of an earthquake. A TREMOR is a slight, rapid shaking of the ground. A TEMBLOR is another term for an earthquake.