Why Do Earthquakes Occur?


An earthquake is the violent perceivable shaking of the earth’s surface due to the seismic waves. The seismic waves are created as a result of the dislocation of the earth’s tectonic plates due to the energy stored in the earth’s crust. The intensity of an earthquake is measured with the help of a seismometer that produces a seismograph. An earthquake is one of the chief examples of destructive forces of nature. An earthquake has a number of dreadful consequences including the loss of lives and destruction of property. It is also known as earth tremor or tremblor.

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Causes of an Earthquake

The main cause of an earthquake is the sudden release of energy when a rock present underground abruptly breaks down into two or more pieces. This release of energy causes the seismic waves, which are further responsible to shake the ground. The broken pieces of the underground rock tend to rub against each other, which causes dislocation of the plates. Hence, an earthquake is mainly caused because of the vigorous movement of the rocks that are present deep inside the earth’s crust; however, some artificial factors may also induce quakes, for example, man-made activities like geothermal plant construction, tunnel building, or dam building, etc. The other reasons may include volcanic eruptions, heavy rain, high CO2 pressure, etc. Also, groundwater extraction causes a significant drop in the pore pressure; therefore, it is yet another reason that leads to earthquakes.

Causes of an Earthquake

Measuring an Earthquake

An earthquake is measured using a machine called ‘seismometer.’ It produces the display of the motion of the ground caused due to seismic waves via a graph. The hard paper format of the graph is known as the seismograph, whereas the digital display is known as a seismogram. The magnitude of an earthquake is basically determined by obtaining the logarithm of the height of the largest seismic wave depicted by a seismograph. In the year 1935, American seismologists Charles F. Richter and Beno Gutenberg devised a unit that was adopted universally to measure the magnitude or size of an earthquake quantitatively known as the Richter scale. A Richter scale is usually numbered 1-10.

Measuring an Earthquake

Consequences of an Earthquake

1. Tsunami 

One of the most crucial outcomes of an earthquake is the plausibility of the tsunami. In seismology, the point on the surface of the earth from where the disturbance is assumed to originate is known as an epicenter. If the epicenter lies offshore, it causes the seabed to get displaced from its original position. In such a case, a tsunami is most likely to occur.


2. Landslides

Landslides get triggered by the intense movement of the ground. The motion leads to dislocation of the base, which disrupts the composition of the rock and loosens it up. The gravitational pull of the earth tends to attract the rock gets towards a downward direction. Since the earthquakes are caused due to the violent motion of the earth’s tectonic plates, they are one of the prominent reasons responsible for landslides and ground failure.


3. Destruction of Property 

Every structure standing on the surface of earth possesses a natural frequency of oscillation known as the resonance frequency. If the resonance frequency of the building perfectly matches the frequency of the seismic waves, the structure tends to exhibit a to-and-fro motion. Due to the vicious trembling of the earth’s surface, the perfectly built buildings and the structures on the ground are liable to experience dislocation and breakdown.

Destruction of Property 

4. Soil Liquefaction

Earthquakes are capable of causing minor disturbances in the original composition and structure of the soil present on the surface by inducing vibrations and motion. This increases the water consistency in the soil, which makes it lose rigidity and collapse or sink. Hence, soil liquefication takes place.

Soil Liquefaction

5. Tectonic Uplift and Subsidence

Earthquakes have two major consequences, namely tectonic uplift and subsidence. Tectonic uplift is the movement of a surface in a vertically upward direction, which generally leads to erosion, whereas subsidence is the movement in the downward vertical direction, which results in burial.

Tectonic Uplift and Subsidence

6. Loss of Lives

Earthquake leads to deaths and injuries. The most common reasons to the loss of life during an earthquake are suffocation, multiple injuries, panic attack, heart failure, etc. People stuck under the debris are susceptible to experience severe injuries. It also leads to severe mental trauma and affects the emotional health of people.

Loss of Lives

Precautions during an Earthquake

1. Keep enough supply of food and water for several days.

2. Safety equipment such as a flashlight, a fire extinguisher, etc. must be kept handy.

3. If during an earthquake, a person is in bed, it is advisory for that person to cover his neck and head with a pillow.

4. When stuck inside a building during an earthquake, the person must take shelter under a rigid table.

5. If a person experiences an earthquake outdoor, he/she must stay away from buildings and approach open areas.

Precautions during an Earthquake

General Trivia 

5 biggest earthquakes in recorded history

Following is the list of the regions that have experienced the highest magnitude earthquakes to date. The list also includes the exact date of occurrence and the magnitude of this natural disaster.

1. Valdivia, Chile, 22 May 1960 (9.5)

2. Prince William Sound, Alaska, 28 March 1964 (9.2)

3. Sumatra, Indonesia, 26 December 2004 (9.1)

4. Sendai, Japan, 11 March 2011 (9.0)

5. Kamchatka, Russia, 4 November 1952 (9.0)

5 biggest earthquakes in recorded history

The reason why Japan is comparatively more earthquake-prone 

This is because of a strong geological reason, which makes Japan the most prone country to earthquakes and tsunamis. Japan is located across the pacific ring of fire. The pacific ring of fire consists of three tectonic plates, which include the Pacific Plate under the Pacific Ocean and the Philippine Sea Plate. This is the reason why the country is susceptible to face quakes regularly, sometimes even on an hourly basis. To overcome the consequences of the disaster, a number of strategies have been developed such as the promotion of the development of earthquake-resistant buildings, phone alert systems, immediate broadcast, frequent drills, and simulation programs, etc.

Japan is comparatively more earthquake-prone

What would happen at a magnitude 10 earthquake? 

A magnitude 10 earthquake is capable to induce vibration or motion in the ground for approximately an hour along with a persistent tsunami; however, the likeliness of a magnitude 10 earthquake is significantly low. Research shows that no fault in the underground rocks is extreme enough to generate a ’10’ intensity earthquake. Hypothetically, such a dreadful earthquake is capable of releasing energy, which is roughly equivalent to the power generated by the explosion of 14,950 megatonnes of TNT. Such high energy is proficient in destroying most of the area around the epicentre.

magnitude 10 earthquake

Myths and Misconceptions

1. Cracks Open and Swallow Whole Cities

One of the chief misconceptions regarding earthquakes is that they can create cracks in the ground bigger enough to swallow the whole city and people into it. The earthquakes can cause certain deformation to the ground; however, swallowing up the entire city is just a fictitious notion, which is often displayed in movies or comics.

2. California Falling into the Sea

A myth persists in the southern regions of California that a high magnitude earthquake might cause it to fall into the sea; however, it is not possible as an earthquake might lead to a slight change in the shape of the coastline but cannot dissolve an entire city.

3. Dogs and Other Animals can Sense Earthquake

A notable change in animal behavior is mostly observed prior to an earthquake; however, one cannot rely on this to predict an earthquake because the change in behavior is not consistent in nature. There are some times when there exists no perceivable change in the behavior of dogs and other animals.

4. Earthquake Weather 

Most people believe that earthquakes occur during earthquake weather. Around the 4th century B.C., a Greek philosopher Aristotle believed that earthquakes were caused when the winds get trapped underground in huge caverns. The trapped wind tends to search for a way out to the surface. The winds trapped below ground mean that there would be a scarcity of wind above ground, making the weather significantly hot. With the advancement in studies, Aristotle was proved wrong; however, his folly is still believed by many people.

5. Big Earthquakes occur Early in the Morning

A  lot of people trust the fact that high magnitude earthquakes often take place early in the morning. A number of studies have been carried out to find a link between time and earthquakes; however, research shows no evident connection between the two.

 Myths and Misconceptions

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