an only travel through solids. Measuring these waves is called seismology.Scientists have known for a long time that the lava, which comes out from volcanoes when they erupt, was from the mantle. The asthenosphere is the probable source of much basaltic magma, this is because the velocity in S-waves is slowed down and partially absorbed in the asthenosphere. This gives the characteristics that the waves are passing through a solid, which the mantle is, but that contains a small amount of liquid. Also when the volcano erupt occasionally they shoot out solid nodules that have come from the solid rock in the mantle, the so-called plumbing of the mantle. These rocks have been broken of and carried out with the flow of the lava, this type of rock is called peridotite and is what mostly makes up the mantle. It is a fairly recent discovery to prove that the mantle of the earth is not the only part of the interior. Seismology is a new discovery this century that enables observations of natural ground vibration signals, basically the study of earthquakes. It can also be the study of artificially generated seismic signals.Scientists then started to record these signals from earthquakes using seismographs, which are set in stations around the world to record the signals. In all some 125 stations exist around the world. They noticed that the P and S-waves did not travel in a straight line through the Earth, they came to the presumption that the Earth's mantle was made up of many different materials. This caused the P and S-waves to travel at different speeds, because of the way the materials conduct the waves at different velocities. The waves also bent as they went from layer to layer, this caused their path through the interior of the earth to be curved.This was then put into practice, so after an earthquake happened in a country the P and S-waves were sent out. Further around the globe the waves were expected to be received after a couple of mi...
