The upper mantle forms part of the Earth's lithosphere, where earthquakes and volcanic activities frequently occur along plate boundaries. The upper mantle is separated from the crust by the Mohorivicic discontinuity, commonly referred to as "Moho," which derived its name from the Croatian scientist Andrija Mohorovicic.
The structure of the Earth is traditionally divided into three layers based on composition: crust, mantle and core. The crust, which is the uppermost stratum, is classified into two: continental crust and oceanic crust. The continental crust is mafic to felsic in constitution, while the oceanic crust is generally mafic. The mantle, further divided into an upper and lower mantle, comprises more than 80 percent of the planet's volume. It is primarily made up of ultramafic silicate rocks. In the upper mantle, the most predominant rock type is peridotite, characterized by a distinctive olive green color. Peridotite is similar to olivine, which is the most abundant mineral on this layer. Diamonds are also found on the upper mantle just below the cratons of continental plates. The Earth's core is principally composed of iron and nickel, and it is divided into a liquid outer core and a solid inner core.
The crust and the uppermost portion of the mantle forms the rigid outermost mechanical layer of the Earth. Underneath the lithosphere and still part of the upper mantle is a fluid mechanical layer called the asthenosphere, which is where the tectonic plates move and glide. The constant motion of the plates often trigger the formation of earthquakes.