Tuesday, January 27, 2009
An earthquake is a sudden shaking of the earth's crust. Most earthquakes happen when the edges of plates slide past each other. The rocks jerk suddenly or shudder, making the surface of the earth shake. There are about half a million earthquakes each year, but only about a thousand because any serious damage. When earthquakes happen under the sea, they sometimes make enormous waves, called tsunami.
During an earthquake
The shock waves from an earthquake spread out from a point called the focus. The worst damage happens at a point on the earth's surface called the epicenter. It lies above the focus, often on a fault line.