Earthquake

An earthquake is when the ground shakes. The Earth's outer layer suddenly breaks and moves. This releases energy that makes the ground shake and move. The shaking can be very gentle or very strong. Sometimes earthquakes are so weak that people do not feel them. Other times they are so strong that they throw things and people into the air. Buildings can break and whole cities can be damaged.

The place where the ground first breaks is deep underground. It is called the focus. The spot on the ground directly above it is called the epicenter. That is where the shaking is strongest. Earthquakes happen mostly because of cracks in the Earth's outer layer. They can also happen because of volcanoes or when hillsides slide down. Sometimes people cause earthquakes by digging deep mines or by testing big bombs.

Some earthquakes in history were very bad. In 1976, a huge earthquake hit China. It killed over 300,000 people. In 1960, an even bigger earthquake hit Chile. When earthquakes happen under the ocean, they can push the water up. This creates giant waves called tsunamis that can flood the land. Earthquakes can also cause hills and mountains to slide down.

People try to prepare for earthquakes in many ways. Scientists try to predict when earthquakes might happen. Engineers design buildings that can shake without breaking. People learn what to do if an earthquake comes. Earthquakes have scared and amazed people for thousands of years. Many old stories and beliefs are about earthquakes. Even on the moon and on Mars, the ground shakes sometimes. This shows that earthquakes happen all over space.