The internal structure of the Earth and tectonic processes

The Earth's interior has three main shells: the crust, the mantle and the core. The crust is on average 35–40 km thick under the continents and 5–10 km under the oceans, and it is separated from the mantle by the Moho boundary. The mantle reaches about 2900 km depth and makes up most of the Earth's volume, while the core is divided into an outer (liquid) and an inner (solid) part. The crust together with the solid upper part of the mantle forms the lithosphere, which is split by deep faults into large plates that move over the asthenosphere at a few centimetres per year. Earthquakes and volcanoes are frequent where plates collide or pull apart; such areas are called seismic belts, the largest being the Pacific “Ring of Fire” and the Alpine–Himalayan belt. Because Uzbekistan lies in the Alpine–Himalayan seismic belt, the country sometimes has noticeable earthquakes. Earthquake strength is assessed on a 12-point scale, and a volcano consists of a crater, a vent and a magma chamber.