How does an earthquake occur

Earthquakes are one of the most devastating geological phenomena that exist and, worst of all, they can not be predicted. That is why in most cases, and being of high seismic intensity, they cause numerous material and even personal damages in the territory where they are produced. It is a tectonic movement, the plates that form the earth's crust, but if you want to know more about how an earthquake occurs, do not miss this article from.

Etymology and definition

The word "earthquake" comes from the Latin terra, terrae (nominative and genitive singular): 'earth, from the earth', and motus : 'movement'. Although this phenomenon is also known as earthquake or earthquake, which comes from the Greek σεισμός : tremor or earth tremor.

According to Wikipedia, an earthquake is "a shaking of the earth that occurs due to the collision of tectonic plates, which make up the Earth's crust, and the release of energy in the course of an abrupt reorganization of materials from the earth's crust by overcoming the state of mechanical balance ".

Origin

Although the collision of tectonic plates is often the cause and origin of most earthquakes, it can also be caused by other natural phenomena as well as by man . For example, they can be caused by the violent eruption of a volcano, the force of water accumulated in dams or by nuclear experiments.

Also, where it originates, in an earthquake there are two points: the hypocentre and the epicenter . The first is the point of the interior of the earth's crust where the seismic movement originates and can be superficial (if it occurs less than 70 km deep), intermediate (between 70 and 300 km deep) and deep (at a depth of more than 300 km). While the epicenter is the point on the surface of the Earth where the earthquake is more intense (perpendicular to the hypocenter).

Seismic waves

In the hypocentre, the waves are dispersed in all directions: the first to arrive (and those previously detected by seismographs) are longitudinal waves, primary or P, followed by transverse waves, secondary or S. The difference between them is in the speed of propagation and in the possibility of crossing liquid surfaces, such as the external core, the primary ones being those that propagate at a lower speed. There are also surface waves or L, resulting from the interaction of waves P and S, which are the most destructive, the slowest and those that cause damage.

Intensity scales

To catalog an earthquake and measure its intensity, two scales are used: the Mercalli scale and the Ritcher scale. Mercalli's, of 12 points, has the objective of evaluating the intensity of earthquakes according to the effects and damages caused to different structures; it goes from Grade I (felt by few people) to Grade XII (total destruction). Currently, it is quite discontinued because not everywhere, the same earthquake of equal energy produces the same damage.

On the other hand, the scale of Ritcher - which is also known as the scale of local magnitude (ML) - is what is currently used and it is an arbitrary logarithmic scale that assigns a number to quantify the energy released in an earthquake. This scale is between grade 1.5 to grade 12, although until it reaches grade 2, it is not usually spoken of earthquakes. Also, being logarithmic, a magnitude 4 is not twice the number 2, but 100 times greater.

Effects of an earthquake

  • Primary effects: they are the most direct effects of an earthquake, that is, the agitation of the soil and the rupture of the soil.
  • Side effects : the derivatives of this seismic phenomena. This is the case of aftershocks (smaller earthquakes that occur after an earthquake), changes in the topographic level, avalanches, changes in the water table, floods, tsunamis, etc.
  • Tertiary effects: are the effects that have a longer duration in time and, among others, may be the displacement of people from their residences, loss of jobs, loss of services ...