When there is a sudden movement in the earth’s crust, energy moves in the form of waves . It’s like dropping something into water.

Body waves move through the inner part of the Earth and surface waves travel over the earth’s surface. Body waves can travel very fast—up to 8 km a second. They travel through rock , water and gas . When they reach other places on the Earth’s surface they can be registered there. They are usually the first waves to get to the surface. Surface waves cause the most damage, but they move very slowly. These waves come at the end of an earthquake.


Man-made Earthquakes

Sometimes people can make earthquakes happen. They can fill man-made lakes with water after building a dam—or they test atomic bombs underground. Some of these tests can help scientists find out how quakes happen.