What causes earthquakes?

An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel. read more

The earth has four major layers: the inner core, outer core, mantle and crust. (figure 2) The crust and the top of the mantle make up a thin skin on the surface of our planet. read more

People have known about earthquakes for thousands of years, of course, but they didn't know what caused them. In particular, people believed that the breaks in the Earth's surface--faults--which appear after earthquakes, were caused *by* the earthquakes rather than the cause *of* them. read more