Earthquakes, or seismic tremors, occur at a rate of several hundred per day around the world. A worldwide network of seismographs (machines that record movements of the Earth) detects about 1 million small earthquakes per year. (Encarta)
Very large earthquakes, such as the 1964 Alaskan earthquake, which caused millions of dollars in damage, occur worldwide once every few years. (Encarta)
Moderate earthquakes, such as the 1989 tremor in Loma Prieta, California, and the 1995 tremor in Kbe, Japan, occur about 20 times a year. Moderate earthquakes also cause millions of dollars in damage and can harm many people.
Earthquakes occur along a variety of faults, often miles underground and under the ocean, it is along this boundaries of friction and energy that these events occur. The faults, or fractures, 'rub' together to create enormous amounts of energy, which fuel the movement of the earths crust.
There are a variety of fault movements that can occur ;
These fault movements are known as the following -
The type or form of movement can often dictate the stength of scale of the eartquake. Thrust movement often tends to create the most destructive energy and consequently the most intesnive earthquake.