The Mohorovicic discontinuity is known at the boundary between the Earth’s crust and the Earth’s mantle, and helps define the thickness of the oceanic and continental crust.
Thus, it is defined that the thickness of the oceanic crust is on average 8 km while that of the continental crust is approximately 32 km.
Although it can be thought that this discontinuity constitutes a defined limit, the truth is that to go from the crust to the mantle, this limit is a transition.
Therefore, it can be said that the Mohorovicic discontinuity It is a rocky mass that differs in physical and chemical properties compared to the mantle and crust and that acts as a transitional boundary between these two layers.
How was the Mohorovicic discontinuity discovered?
To determine the different layers that make up the earth, geophysics and specifically seismic are used.
Thus, to determine the depth of this discontinuity it was necessary to study the behavior of P waves as follows.
By studying the P waves that are generated when earthquakes occur in the crust, the average speed under the earth’s surface began to be defined and it was discovered that at depth there are always variations in the speed of the P wave.
These variations in speed are interpreted as the earth is divided or made up of layers that have different chemical composition and different physical properties, such as different densities.
The velocity of shallow P-waves and deeper P-waves were then compared with a seismograph or receiver further away compared with a wave receiver closer to the epicenter.
And it was observed that the deepest P waves became faster than the most superficial P waves, that is to say that the deep waves reached the most distant receptor first.
What made us think that the density and physical properties of the most superficial layer were different from the rocks that were deeper.
And so it was, that it was concluded that this variation in speed corresponds to two different layers, the earth’s crust and the mantle.
Subsequently, Andrija Mohorovicic determined at what depth exactly this change began to occur and defined the Mohorovicic discontinuity and the boundary between the mantle and the earth’s crust.
What is the depth of the Mohorovicic discontinuity?
We already know that this discontinuity marks the limit between the crust and the mantle, but now we are going to see what its average depth is.
It has been discovered that, in the oceanic basins, that is, in the oceanic crust, it reaches an average depth of 8 km.
While the continental crust or the continents is more variable, but goes to about 32 km deep on average.
In addition, today it is known that in the center of the continents or cratons the crust becomes thicker and it is here where this discontinuity and limit of the crust and mantle can even reach 70 km depth.
The following map illustrates the thickness of the earth’s crust and therefore the depth of the Mohorovicic discontinuity.
Notice how the thickest areas (red and dark brown) are under some of the most important mountain ranges on Earth, such as the Andes (western South America), the Rocky Mountains (western North America), the Himalayas (northern India in south-central Asia), and Urals (north-south trend between Europe and Asia).