The theory of plate tectonics is mainly used to describe the structure of the outermost layers of the Earth and to explain the cause of earthquakes.

The outermost part of the Earth is called the lithosphere, which is made up of cold, rigid and moveable rocks. The average thickness of the lithosphere is about 100 km. Below the lithosphere lies the asthenosphere, which is made up by liquefied materials with high viscosity. Under high temperature and high pressure, these liquefied materials develop plasticity and make the lithosphere flow above it.

The basic concept of plate tectonics is that the lithosphere is divided into a few nearly rigid plates, including the Eurasian plate, American plate, African plate, Indian plate, Pacific plate, Antarctic plate, and a few other notable minor plates (see the picture below). These plates are subjected to different tension, pressure, gravity, and convection in the mantle. Hence, these plates move slowly every year by several centimeters, with different speeds of movement. This results in the existence of differences in the relative velocities between neighboring plates. Most earthquakes, volcanoes, and orogenesis are the result of the interactions among the neighboring plates.

There are three types of plate boundaries: