Correct Answer: earthquake

Solution : The correct answer is earthquake.

Earthquake or the shaking of the ground is a natural phenomenon in which tectonic plates of the earth moves abruptly, which leads to release of energy at certain point creating seismic waves. The point inside the earth on which earthquake takes place is known as hypocenter and the point just above it on the surface of ground is known as epicenter. It is measured using Richter and Mercalli scale. Richter scale measures the magnitude of the earthquake and the Mercalli scale measures its intensity.