Earthquakes are sudden movements of the ground. They cause ripples called seismic waves that can be felt around the world. About a half-million earthquakes shake the Earth every day, but most of them are too small to be noticed. The ones we feel are caused by movement along faults in the Earth’s crust. The spots on the Earth’s surface directly above where rock breaks are called focal points or epicenters. The energy from the breaking of rock is released in bursts that are felt as earthquakes.
The Earth’s skin is like a puzzle that is made up of many pieces of different sizes and shapes. These pieces, known as tectonic plates, are constantly sliding past each other and bumping into each other. Sometimes a plate gets stuck to another one and builds up pressure. When enough pressure is built up, the pieces of the plate jerk suddenly together, causing an earthquake.
Some places are more prone to earthquakes than others. Most large earthquakes happen in three major zones of the world:
The most active zone is the circum-Pacific seismic belt, which stretches around the Pacific Ocean from Chile to Alaska. About 81 percent of the world’s largest earthquakes have happened in that area. The other two zones are the Alpide belt, which runs across Asia through India and Nepal; and the Mid-Atlantic Ridge that runs under the Atlantic Ocean.