According to the U.S. Geological Society, the area in the Earth's crust where an earthquake forms is called the hypocenter. Unpredictable in nature, earthquakes form when energy from the crust is released, causing vibrations on the surface of the earth. The magnitude of earthquakes can vary exponentially, and the stronger the magnitude, the more devastating the effects, especially on areas that are near the epicenter.
The earth's crust is made up of several plates that are constantly moving. These movements are relatively slow, but they may cause earthquakes. Large earthquakes occur when the plates collide or slide past each other. The release of energy can be powerful enough to trigger an earthquake.
The boundaries where the two plates meet is often the focal point of the earthquake. However, sometimes it can spread across several other areas. Earthquakes are often located on faults. Faults are the result of fractures in the Earth's crust when the plates move.
Whenever an earthquake strikes, the major quake is sometimes preceded by foreshocks and followed by aftershocks. Foreshocks will often multiply in magnitude right before the quake; aftershocks are the opposite, and will decrease in magnitude once the quake is over. Strong earthquakes can cause avalanches and tsunamis. The magnitude of an earthquake is usually measured by a Richter scale. The Richter scale measures the amount of energy released during the earthquake.