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Astenosphere, one of the many inner layers of the Earth on which we certainly cannot walk but that does not mean that we should not care. Deeply, phenomena take place that have strong consequences for us and for all the creatures that are on it surface of the planet.
The asthenosphere is a rather superficial belt of the Earth's mantle because it is found just below the lithosphere but above the mesosphere. It is between 250 and 300 km deep and is one of those layers where the rocks are partially fused and not quite solid as in others. This has some important consequences.
Astenosphere: convective motions
THE convective motionsi, as we can guess, are closely related to the fact that the rocks in the asthenosphere are not solid. It was precisely noting how the speed of propagation of the seismic waves in this layer, which has begun to pay attention to this mantle band with particular characteristics so much that it deserves to be distinct and defined with its own name.
In the asthenosphere the speed of seismic waves of shear decreases considerably, being proportional to the rigidity of the vehicle, therefore this band is called zone at low speed or LVZ (“low-velocity zone”).
The material that we find there is a sort of very high viscosity fluid in which isostatic movements are observed linked to the fact that there are variations in the weight of the earth's crust. In the asthenosphere convective motions take place, ordered motions in convective cells whose energy is transferred to the lithosphere producing the evolution of the plates that constitute it.
We talk about plastic asthenosphere not because it contains plastic, not so far, at least, but because of its physical characteristics. We have said in fact that it is one low speed zone in which the seismic waves suffer severe slowdowns. This is because the matter is almost "plastic" unlike what is found for example in the lithosphere.
Located between 70 and 250 km of depth, the asthenosphere is made up of rocks which are close to melting point, which is why they show a behavior which we have defined plastic. The temperature is therefore greater than 1,000 ° C.
When it comes to asthenosphere we mean what we find by investigating what is "inside" the planet Earth. At the moment we are sure that this band exists under the oceanic crust, because probably under the continental crust it is necessary to dig deeper to find it.
The fact is that it exists, since 1926 it has been talked about and studied even if the confirmation came in conjunction with the Great Chilean Earthquake of 22 May 1960. Still the asthenosphere plays an essential role in T.global heptonic of the lithosphere.
The curious may perhaps wonder why this name. It comes from the Greek asthenēs, which means 'weak', side by side in a "sphere".
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- Mesosphere: earth and gas
- Lithosphere: meaning