The ground we walk on is actually the surface of a number of separate thick plates of solid rock which rest on Earth’s mantle of melted rock.
We know that our present continents were created by the movements of these plates, coming together and splitting apart. The plates are called tectonic plates; tectonic means “coming together and breaking apart.”
The plates continue to move and, consequently, they sometimes run into each other, slide against each other, and slip one on top of the other. This underground movement is sometimes reflected on the surface of Earth by earthquakes.
While tectonic plates are constantly moving, they usually move very slowly. The crust of Earth does not reflect every movement, but stores up the energy from the movement inside its rocks until they can no longer bear the strain.
At that point, the energy is released through the weakest points in Earth’s crust, causing the ground to suddenly move: earthquakes.