Did you know that almost 500,000 earthquakes happen every year? Of course, they all have different magnitudes and many are imperceptible unless you have access to a seismometer. The truth is that earthquakes are a natural phenomenon that arouses a lot of curiosity, possibly because they are unpredictable.
What is an earthquake
Simply put, the word earthquake means “earth in motion” and it comes from Latin. However, in more technical terms, an earthquake is defined as a sudden movement or vibration of the earth’s crust that is produced by the release of energy, contained from inside the Earth, in the form of seismic waves.
Earthquakes can be classified according to their origin, their magnitude and more ways, but all of them are characterized by being transitory, that is, they do not last more than a few seconds or, sometimes, minutes. As for its origin, there are some concepts necessary to understand the entire phenomenon. One of these concepts is the hypocenter of an earthquake , defined as the point of origin of an earthquake. Another important concept is the epicenter of an earthquake , which is nothing more than the point on the earth’s surface that is above the hypocenter. Next, we will know how they are produced, that is, their origin, among other details.
Earthquakes are generated mostly by tectonic activity . This activity is based on the theory that the Earth’s surface, or better known as the Lithosphere, is made up of tectonic plates that slide and can collide with each other, hence the tectonic activity arises. It is precisely this movement and collision between plates that causes the vast majority of earthquakes. Here you can learn more about what the lithosphere is .
However, there are many other causes that can trigger earthquakes and from these causes an extensive classification arises that we will detail in the next section. Also, in the video below you can learn more details about what an earthquake is and how it occurs.
As we mentioned, according to the cause for which the earthquakes originate, they can be classified into two large groups:
Earthquakes due to natural causes
- Tectonic earthquakes: those associated with tectonic plates, generally occur in areas of contact between different tectonic plates or, rarely, in areas of weakness within the plates. Tectonic earthquakes are the most frequent.
- Volcanic earthquakes: those earthquakes that are generated by the fractionation of the rock product of the volcanic activity of a region. We recommend you read these Green Ecology articles on How volcanoes form and Types of volcanic eruptions .
- Collapse earthquakes: those that are associated with sudden displacements of rock or earth masses. For example, earthquakes that occur after a rapid slide down a hillside.
- Earthquakes due to meteorite impacts: on planet Earth they are very rare, but throughout history there have been some earthquakes caused by the violent shaking that occurs when a meteorite hits the ground.
Earthquakes from anthropogenic causes
- Earthquakes induced by large reservoirs: those earthquakes produced by the overload of dammed water and the sudden changes that occur when it is released.
- Earthquakes from nuclear or mine and quarry explosions : Nuclear explosions can produce earthquakes of medium magnitude, while explosions from mines and quarries can produce earthquakes of smaller magnitude.
- Earthquakes induced by oil extraction: hydraulic fracturing or fracking is a technique used to extract gas and oil. It usually causes micro-earthquakes and sometimes larger earthquakes by breaking the ground.
There are many ways to measure earthquakes, some scales measure the magnitude of the earthquake, others simply measure the intensity. However, the most widely used scale is magnitude and is called the Richter scale or local magnitude scale ( M ). It is a logarithmic scale of magnitudes and is obtained from the relationship between the force and the energy released. Precisely the Richter scale makes it possible to measure earthquakes of magnitude 2 to 6.9 and depths from 0 to 400 kilometers.
For its part, the seismological scale of magnitude of the moment , is also frequently used since it allows to measure earthquakes of magnitudes greater than 6.9 and to determine with more precision the extreme values. This scale also measures the stiffness of the rock and the average distance of displacement.
Depending on the magnitude and intensity of the earthquake, there are many consequences that can be caused. Let’s see here:
- Rupture of the ground: it is one of the most common effects observed after an earthquake, causing significant damage to buildings and infrastructure of roads and highways, among others.
- Floods: after the earthquake, floods can arise as a result of the rupture of dams or the sliding of river beds, which generate collapse. Here you can read about the Causes and consequences of floods .
- Landslides: with the abrupt movement of the tectonic plates, certain instability is generated in valleys and mountains that promote landslides.
- Tsunamis or tidal waves: this type of phenomenon is based on the vertical displacement of large masses of water as a set of waves with great energy and variable size. Tsunamis are produced by various causes, including earthquakes in the middle of the sea or earthquakes whose epicenter is near the sea. In this other post you can learn more about How tsunamis are formed .
- Impacts directly to humans: although all the effects just mentioned cause numerous impacts on human life, they could be considered indirect. Earthquakes can directly cause injury and even death. Once the earthquake is over, depending on the damage it has caused, inaccessibility to basic services, food shortages, diseases, etc. may occur.
Now that you have been able to learn all this about what an earthquake is, how it occurs, its types and more details, we encourage you to know the volcanic and seismic regions of the world , where more earthquakes and volcanoes occur.