This link has lots of facts about earthquakes. An earthquake is a sudden shaking of the earth caused by the breaking and shifting of rock beneath the earth's surface. Earthquakes can cause buildings and bridges to collapse, down telephone and power lines, and result in fires, explosions and landslides. All of these are earthquakes. Aftershocks are smaller earthquakes occurring after a main shock, and they keep the hazard relatively high for a certain period after any large earthquake.
Foreshocks are smaller earthquakes occurring before a main shock.
Only with hindsight can we distinguish what are foreshocks and aftershocks. There are many earthquakes in Japan, but the majority are small ones. Even so, the possibility exists that a major earthquake will occur, in which case buildings may collapse, fire may break out, and other serious damage may occur. Today, its importance comes more from the wealth of scientific knowledge derived from it than from its sheer size. Top of Page About Earthquakes Frequently asked questions Click here to find a list of answers to frequently asked question about earthquakes.