The tectonic plates of which the earth's crust is formed are in continuous movement, but this tends to be slow and imperceptible. However, when something impedes this displacement and collide with each other, a large amount of energy begins to accumulate that ends up releasing suddenly when there is a sudden movement of these plates. This energy emerges on the earth's surface in what we know as an earthquake.
This type of earthquake, called tectonic, covers the vast majority of earthquakes that exist. The other type of earthquake, less common, is the volcanic, which is produced by volcanic action due to the expansive force of the gases and vapors that produce explosions when the magma rises through the chimney of the volcano.
The point at which the earthquake is detected on the surface is the epicenter and the point where the earthquake occurs is the hypocenter.
In the hypocentre, the waves disperse in all directions. The first that arrive are the P waves (primary), followed by the S waves (secondary). They differ from each other in the speed of propagation and in the possibility of traversing liquid surfaces, such as the outer core. Primaries are those that are detected first in the seismograph and propagate through the liquid medium at a lower speed, something that S waves can not.
There are also the L waves, the surface waves, these are on the surface and are the most destructive, they are also the slowest and are the ones that cause the damage.
To catalog an earthquake, two scales are used: the Mercalli scale and the Ritcher scale. The first one is already discontinued because it measures the intensity of the damage caused by an earthquake. And I say that it is discontinued because not everywhere, the same earthquake of equal energy produces the same damages, since they affect other variables, such as structures. With this scale, a grade 5 would be that all objects fall, or grade 10 that would be something like all wooden structures being destroyed, rails bent, etc.
The scale that is currently used is the Richter scale, in it, the energy released by the earthquake is measured. What stands out from this scale is that it is logarithmic, which means that a grade 6 earthquake is 10 times stronger than grade 5 earthquakes, or that for example a grade 9 earthquake is 1000 times stronger than a grade 6 earthquake. .
So you can see what I am telling you and so that you know the amount of energy that our Planet can release in one of these earthquakes, I will tell you that in the Haiti Earthquake on Tuesday it was cataloged as 7.5 degrees and that it would be the equivalent in energy as 750000 tons of TNT (trinitrotoluene). This, as you can understand, causes total destruction.