Earthquake – Concept, elements, types, causes and consequences

We explain what an earthquake is, how it occurs, its elements, causes and consequences. Also, what types of earthquakes exist.

What is an earthquake?

It is called an earthquake (or earthquake), tremor, earthquake or earthquake to the violent, sudden and transient shaking of the Earth’s surface, produced by the release of energy accumulated in the subsoil, in the form of seismic waves that travel outwards. That is, they are regular and sudden movements of the earth’s crust, which occur as a consequence of various natural geological phenomena.

Depending on their intensity, earthquakes can be almost imperceptible or bring gigantic disasters, not only because of their direct impact on life on the earth’s surface, but because can lead to other destructive phenomena, such as tsunamis, volcanic eruptions or land cracks.

For this reason, and because they are difficult to predict accurately, earthquakes have been a source of fear for humanity since time immemorial.

Paradoxically, earthquakes give us a lot of information about the interior of the planet. Many institutions are dedicated to recording the movements of the earth’s crust and predicting its surface effects, in order to develop construction and engineering technologies that are more resistant and less affected, helping to prevent tragedies. This science is called seismology.

How does an earthquake occur?

Earthquakes occur when, due to some underground phenomenon (generally plate tectonics itself), energy accumulates in the earth’s subsoil, due to the set of forces that take place there, which include gravity, pressure, the high temperatures of matter and the resistance of compacted materials over the millennia.

This energy must eventually be released through waves that shake matter. It will always do so according to the physics of the elements of the subsoil, moving in all directions, and as they move towards the earth’s surface they increase in intensity, when they find softer materials.

Causes of earthquakes

The main causes of an earthquake are natural, although they can also occur as an exceptional consequence of certain human activities. A list of common causes would include the following:

Natural causes:

• The collision and friction of two tectonic plates, which not only gives rise to seismic movements, but also different types of orogeny and geological changes.
• Violent eruptions of volcanoes, which shake their surroundings as the retained magma bursts to the surface.
• Massive landslides such as avalanches or subterranean geological subsidence, such as the collapse of cave roofs.
• Very abrupt variations in atmospheric pressure, as in the case of cyclones.

Human causes:

• The sustained use of geothermal power generation, by suddenly cooling the subsoil by introducing water to evaporate, it can cause small local earthquakes.
• The “fracking” or hydraulic fracturing for the extraction of hydrocarbons, a technique that consists of increasing the cracks or ducts in which the desired substances are housed, injecting water at very high pressures.
• Underground nuclear explosions and other warlike experiments of great intensity.

Consequences of earthquakes

An earthquake may well have no visible consequences, at least for those of us on the surface. But it can also bring more or less disastrous consequences, capable of costing many lives, such as:

• Landslides and landslides, such as avalanches, landslides or partial landslides of land elevations.
• Soil breaks and liquefactionSince when surface materials are subjected to sudden and intense movement, they can break, separate or lose their cohesion, in the latter case becoming a white or semi-liquid substance.
• Tidal waves, floods and tsunamisIn cases where the tremor occurs in the vicinity of large bodies of water, the waves can be transmitted to the liquid and produce large waves of oversized size and other unusual behavior.
• Fire and urban damage, as a consequence of the collapse of buildings, exposing gas pipes and collapsing power lines.

Types of earthquake

Depending on their tectonic characteristics, earthquakes can be classified into:

• Interplate earthquakes, also known as subduction earthquakes, occur in regions of contact between two tectonic plates, when the pressure between them overcomes the mechanical resistance that locks them and a displacement occurs in some direction. Its intensity, in fact, depends on the amount of movement produced.
• Medium and high depth intraplate earthquakes, similar to the previous category, but produced inside the plate and not at its ends in contact with another. They are, however, much less common.
• Cortical or superficial earthquakes, produced at shallow depth, as a consequence of the deformations and stresses suffered by the continental plates of the lithosphere, when they are at a point of convergence of tectonic plates.
• Oceanic plate earthquakes, produced as their name indicates in submarine tectonic plates, especially at the beginning of subduction processes, are usually associated with tidal waves.
• Transforming fault earthquakes, produced by the collision of two tectonic plates, but not in the same place of the meeting, but much further, due to the transmitted forces and the lateral displacement produced between the found plates.

On the other hand, a second common way of classifying earthquakes is one that takes into account the depth of their focus. According to this, we would have only three categories:

• Surface earthquakes, produced in a strip of the earth’s crust no more than the first 70 kilometers deep.
• Intermediate earthquakes, produced in a greater depth that oscillates between 70 and 300 kilometers underground.
• Deep earthquakes, produced outside the limits of the lithosphere, beyond 300 kilometers of depth.

Elements of an earthquake

The systematic study of earthquakes has revealed that they have certain common elements, such as:

• The seismic focus or hypocenter, which is the point of origin of the underground earthquake, found at some point in the lithosphere.
• The epicenterInstead, it is the vertical projection on the earth’s surface of the hypocenter, that is, the point on the latter that is directly above the focus of the earthquake, and is the place where the greatest amount of damage traditionally occurs.
• The magnitude, which is the force or intensity with which the earthquake occurs, and which can be measured on different seismological scales, the most famous of all being the Richter Scale, named after the American seismologist Charles F. Richter.