Earthquakes are natural phenomena that can cause extreme disasters if they happen, so we consider that their study and understanding is of great importance to avoid catastrophic loss of life, prevent major damage to homes and buildings, and prevent it from occurring. great economic losses in a region.
This article explains in detail everything that is currently known about earthquakes, how they occur, the types that exist, related terms and how to act when faced with them.
What are earthquakes?
Earthquakes are natural geological phenomena caused by the sudden and rapid movement of a large volume of rock. The violent tremors and destruction caused by earthquakes are the result of breaking and sliding along fractures in the Earth’s crust called fault lines.
Larger earthquakes result from the rupture of larger fault segments. The origin of an earthquake occurs at depths between 5 and 700 kilometers, at the focus. The point on the surface directly above the focus is called the epicenter.
During big earthquakes, a massive amount of energy is released as seismic waves, a form of elastic energy that causes vibrations in the material that transmits them. Seismic waves are analogous to the waves produced when a stone (rock) is dropped into a pool of water.
Just as the impact of stone creates a pattern of moving waves, an earthquake generates waves that radiate outward in all directions from the focus.
Although the seismic energy dissipates rapidly with increasing distance, sensitive instruments located around the world detect and record these events.
Thousands of earthquakes occur around the world every day. Fortunately, most are so small that they can only be detected by sensitive instruments. Of these, only about 75 earthquakes are recorded each year and many of them occur in remote regions.
Occasionally, a large earthquake is triggered near a major population center. Such events are among the most destructive natural forces on Earth.
Ground shaking, along with the liquefaction of soils, wreaks havoc on buildings, roads, and other structures.
Also, when an earthquake occurs in a populated area, power and gas lines often break, causing numerous fires.
In the famous 1906 San Francisco earthquake, much of the damage was caused by fires that became uncontrollable when burst water mains left firefighters with only droplets of water.
Parts of an earthquake
The place inside the Earth where rocks break and slide, or the place where an explosion occurs, is the hypocenter or focus of the earthquake. Energy begins to spread out from the focus. The point on the Earth’s surface that is directly above the focus is the epicenter, so maps can represent the position of epicenters.
Hypocenter or focus
The hypocenter is the focus of the earthquake, that is, it is the point, place or area where the expansion of seismic waves begins towards the surface, the hypocenter can be taken as the origin nucleus of the earthquake.
Epicenter
The epicenter, on the other hand, is a straight vertical projection of the hypocenter on the surface of the earth, this area is usually the one that receives the greatest damage from the earthquake, as it is the one that first receives the seismic waves because it is the closest point to the hypocenter..
Fault plane
Earthquakes generally occur in a fault zone or plane where large blocks of rock slide.
Therefore, the fault plane is where the focus of the earthquake is located.
In this case, geologists distinguish at least four types of faults: reverse, normal, transcurrent, and mixed.
Causes of earthquakes
Ancient cultures offered a variety of explanations for seismicity (earthquake activity), most of which involved the action or mood of a giant animal or god.
Currently scientific studies suggest that an earthquake can occur for a number of reasons, including:
- The sudden formation of a new geological fault (a fracture or rupture where slippage occurs between rock masses)
- Sudden slip on an existing fault line, i.e. the movement of an active fault line
- A sudden change in the arrangement of atoms in minerals in rocks.
- Movement of magma in the magma chamber or explosion of a volcano.
- A giant landslide
- a meteorite impact
- An underground nuclear bomb test.
- Small earthquakes or tremors caused by fracking (hydraulic fracturing of rocks) in the extraction of hydrocarbons in oil shale
Of these various reasons, faulting related to plate tectonic movements is the most significant. In other words, most of the earthquakes They are due to the movement or displacement of geological faults.
Classification of earthquakes and earthquakes
According to its origin
The table shows that earthquakes can be classified as natural (occur naturally) and artificial (caused by humans).
| natural earthquakes | artificial earthquakes |
| intraplate | nuclear bomb tests |
| interplate | Underground and surface explosions |
| Due to geological faults | Fracking (hydraulic fracturing of rocks) |
| Volcanism and volcanic eruptions | |
| meteorite impacts | |
| Landslides |
According to your location
Earthquakes could also be classified into those that are generated in intraplate and those that are generated in interplate.
| interplate earthquakes | They are those that occur or generate at the limits of tectonic plates (convergent, divergent and transform). |
| intraplate earthquakes | They are those that are generated inside the tectonic plates. |
For its depth
Another classification can define the types of earthquakes as superficial, intermediate and deep.
| Shallow earthquakes | They are those that are generated at a depth of less than 70 km in the crust and are usually the most destructive. |
| intermediate earthquakes | They are those that are generated at a depth between 70 km to 300 km, depending on their intensity and magnitude they can be destructive. |
| Deep earthquakes (bathysisms) | They are those that are generated at a depth greater than 300 km, these practically occur in the mantle and are only usually detected by special seismographs. |
Types of earthquakes
Now, since the classification of earthquakes has been explained, according to their origin, location and depth, each of the types will be described below.
| types of earthquakes | Description |
|---|---|
| interplate | They are those that are generated at the limits of tectonic plates (convergent, divergent and transform). |
| intraplate | Are those that occur within the tectonic plates (continental and oceanic) |
| due to geological faults | They occur due to the activity and movement of active geological faults. |
| volcanic | They are generated by the movement of magma within the magma chamber and by volcanic eruptions. |
| due to meteorite impact | Occurs when a meteor strikes the surface of the earth |
| by nuclear explosions | Earthquakes that are generated by the explosion of nuclear bombs, generally test |
| by landslides | Earthquakes generated by large volume landslides |
| by fracking | Earthquakes caused by hydraulic fracturing of rocks under the surface in the extraction of unconventional hydrocarbons |
| by mining explosions | Earthquakes generated by explosions that fracture rocks in surface and underground mines |
The following describes the different types of earthquakes and earthquakes that are named in the table.
Earthquakes and earthquakes at tectonic plate margins
When observing the image, it can be clearly distinguished that the greatest number or percentage of earthquakes that occur on the planet occur at the limits of tectonic plates and it is that in these limits tectonic plates are generated and destroyed, they are also associated with a large number of movement and volcanism, which in turn produce a large number of earthquakes.
In addition, we can add that this large number of earthquakes coincide with what is called the Pacific ring of fire, which is where there is the greatest amount of volcanic and seismic activity on the planet.
As mentioned, these earthquakes occur at plate boundaries and are known as interplates, so what are the different types of plate boundaries that exist? How are earthquakes generated in these limits?
Earthquakes at convergent boundaries
At these limits, a lithospheric tectonic plate subducts or slides under another tectonic plate, either continental or oceanic. This landslide produces friction between large masses of rocks, especially in the coastal areas of the continents in the Pacific ring of fire.
It is here where the potential for a large earthquake to occur is very high due to the accumulation of energy that occurs in subduction zones.
These limits are related to the construction of mountains, and one of the examples is the Andes mountain range in South America that has been formed by the collision of the Nazca plate with the South American plate.
For this reason the subduction zone in South America is highly seismic, and there have been large earthquakes along that coast due to the subduction of the Nazca Plate under the South American Plate, an example of this was the earthquake of April 16 of 2016 in Ecuador.
Earthquakes at Divergent Boundaries
In this case, the tremors or earthquakes occur in the so-called oceanic ridges, in these areas is where new oceanic lithosphere is generated every day and there is a large number of volcanic processes.
In this case, the earthquakes are not of great magnitude and are mainly related to volcanism. Remember that tremors can also be generated by the movement of magma in the magmatic chambers of volcanoes.
The potential for large-magnitude earthquakes to be generated in this sector is very low.
Earthquakes in transform boundaries
In this type of tectonic plate limits, what happens is that a slip is generated between large masses of rocks belonging to the lithosphere through a large vertical fault, this is the typical example of the San Andreas Fault, which has a large potential to generate a highly destructive earthquake.
This is due to the fact that between types of limits or geological faults, the sliding between the rocks through the fault plane is quite superficial, and the earthquake that is generated will be very close to the surface, and the closer the earthquake occurs,