Earthquake is a severe natural disaster that impacts lives on Earth. Scientists and seismologists work towards understanding the cause of an earthquake and focus on predicting the occurrence of an earthquake. Waves are produced under the Earth’s crust resulting in causing tremors on the Earth’s surface. The release of energy that is stored under the Earth’s crust is the main cause of their waves that eventually result in earthquakes.

The word “Earthquake” is a combination of ‘Earth‘ and ‘quake‘; ‘quake’ means to tremble or tremor. The first known Earthquake in India was recorded in Saldang, Karnali zone on June 6, 1505. Although on January 26, 2001, Bhuj in Gujarat recorded the most violent earthquake to ever occur in our country. This article aims to discuss the details related to earthquakes.

What is an Earthquake?

Earthquake is shaking of the earth’s surface caused by the passage of seismic waves through the rocks above the crust, releasing strain energy in the earth’s crust. This results in the formation of waves radiating outwards from the earthquake source. It usually occurs near the geologic fault lines or the narrow zones where rock masses move with respect to one another.

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Very little was known about Earthquakes till the late (20^{\rm{th}}) century; with the development of seismology, the scientific study of the aspects of an earthquake, we can finally answer the questions regarding the causes of an earthquake.

Earthquakes are among the major deadly natural hazards. There are around (100) earthquakes annually of a size that would cause severe damage. They strike suddenly, and lots of the earth’s earthquake zones coincide with areas of high population density. Large earthquakes can cause catastrophic loss of human lives and an immense loss to a region’s economy.

Earthquake: Description

The sudden movement of tectonic plates in the earth’s crust can lead to an earthquake. Tectonic plates cover the earth’s entire surface, and at the fringes of these plates lie major fault lines. When the stress in the earth’s crust exceeds the strength of the rock, it causes it to break along the lines of weakness, which could be either a pre-existing one or along an entirely new fault plane.

The point from where an earthquake originates below the earth’s surface is called focus or hypocenter, and this point can be many kilometres within the earth. On the earth’s surface, the point directly above the focus is called the epicentre of an earthquake. The tectonic plates continuously move over the earth’s surface, but when one tectonic plate moves over the other, leading to a possibility of orogeny, which can result in an earthquake.

Earthquake: Causes

Earth’s structure consists of four main layers: inner core, outer core, mantle and crust. Crust and the top part of the mantle act like a thin layer of skin on the surface of our planet. This layer of skin covering the earth’s surface is not uniform or in one piece; instead, it consists of many parts, much like the pieces of a puzzle. These puzzle pieces are continuously moving and slowly sliding past and bumping into one another. These puzzles are the tectonic plates, while the edges of these plates are referred to as plate boundaries. Most earthquakes occur in the faults that lie within the plate boundaries all over the world. Due to the friction between the plates, the rough edges stick to each other while the remaining parts move. When the plate has moved a certain distance, the edges move apart, leading to an earthquake.

Earthquake: Techniques to Measure

We can measure an earthquake using Richter’s scale, and a seismograph is an instrument that is used to record an earthquake. The recording of a seismograph is known as a seismogram.

A seismograph is kept over the earth’s surface, and when the tremor strikes, the entire set-up starts shaking with it. It is attached to a mass and spring, and due to its inertia, this mass does not shake. As the seismograph shakes, under this mass, it records the relative motion between itself, the rest of the instrument, and the earth’s surface (which is shaking).
Then using a Richter scale, we determine the strength and magnitude of the earthquake.

The strength, or magnitude, of an earthquake, is measured using the Richter scale. The earthquakes that measure around \(7\) or \(8\) on the Richter scale can cause massive devastation. The earthquakes of magnitude \(3\) or below are rarely felt. On May 22, 1960, the largest earthquake ever recorded in Chile was a magnitude \(9.5\) on the Richter scale.

Earthquake: Impact

Earthquakes bring devastation and a massive loss to life and property. Many buildings, schools, hospitals etc., get destroyed due to it. Many people lose their lives or get severely injured. It wrecks hell on the region and on the life of people in that region.
The environmental effects of earthquakes include surface faulting, tectonic uplift and subsidence, tsunamis, soil liquefaction, ground resonance, landslides, and ground failure. Earthquakes can further lead to forest fires and trigger flooding due to the wrecking of dams or reservoirs.

Earthquake: Preparedness

Disasters cause by natural factors and can’t really be predicted. Although an earthquake can strike anywhere, some regions see a lot more tectonic plate movement close to the fault lines making them much more prone to Earthquakes. Such regions are called seismic zones. In India, Ladakh, Himachal Pradesh, Rann of Kutch and Andaman and Nicobar Islands come under very severe intensity zone. People living in or around a seismic zone should be educated about how they can, on a personal level, minimize the damage caused by earthquakes. We cannot prevent a disaster, but we can always learn what to do before, during and after such a disaster to protect ourselves and those around us.

Do’s and Dont’s: Before an Earthquake

1. The connections of electric lines, gas pipelines and appliances must be made flexible.
2. Every individual should be aware of their locality’s earthquake readiness plan.
3. Local people should be aware of their closest shelter house, canned food supply house.
4.  All houses and buildings must have an up to date first aid kit, dust masks, goggles, firefighting equipment, a torch, and gallons of water.
5. Before starting the construction of buildings in earthquake-prone areas, Architects and structural engineers must be consulted.
6. Buildings should be manufactured according to the rules and regulations laid by the disaster management committee.
7. Awareness must be spread among community members about the measures mentioned above. A hierarchy must be set up in case evacuation plans need to be set up. For that, the most vulnerable section of the region must be identified.

Do’s and Dont’s: During an Earthquake

1. All people must stay indoors until the shaking stops and till an official announcement is made that it is safe for people to exit.
2. People who are outside should take cover under the closest shelter place set up by the government.
3. Inside the building, one must avoid windows, bookcases, furniture, heavy appliances that may fall due to the shaking of the ground.
4. The shelter should be taken under a table or bed and held on to a post or other fixture. The students should be advised to cover under their benches.
5. People should be advised to stay away from electric poles, power lines or trees.

Do’s and Dont’s: After the Earthquake

1. First aid kits must be used to treat people with minor injuries such as cuts, scrapes, minor bleeding and bruises.
2. People injured severely must not be moved until they are out of danger and proper medical help has arrived.
3. Rescue breathing must be given to a person who cannot breathe, and CPR must be administered if the person has no pulse.
4. Electric wires or switches must not be touched with bare hands to avoid shocks. The main power switch should be switched off.
5. Fallen items, tumbling shelves must be taken care of and avoided.
6. Damaged walls and broken glass must be tended to and cleared out.
7. Gas valves should be thoroughly checked for leaks and ensure that any broken appliances are not plugged in before getting the damage repaired.

Summary

Earthquake is the sudden shaking of the earth’s surface due to the passage of the seismic waves through the rocks over the crust, due to which there is a release of strain energy in the earth’s crust. This results in the formation of waves radiating outwards from the source of the earthquake. Due to the friction between the plates, the rough edges of the plates stick to each other while the remaining part of the plate continues to move.

Learn about Transverse and Longitudinal Waves

Frequently Asked Questions

Frequently asked questions related to earthquake are listed as follows:

Q.1. What is an Earthquake?
Ans: An earthquake is the sudden shaking of the earth’s surface due to the sudden release of energy over the earth’s crust, resulting in seismic waves moving outwards from the point of origination of the earthquake.

Q.2. What is Richter scale?
Ans: Richter scale is the numerical scale used for expressing the magnitude of an earthquake based on the recordings of a seismograph.

Q.3. What is the epicentre of an Earthquake?
Ans: The location on the earth’s surface, which is exactly above the point of origination of earthquake below the earth’s surface (or the hypocenter), is called the epicentre.

Q.4. Do earthquakes happen on other planets?
Ans: Earthquakes generally happen on a planet with a very hot core, much like the earth’s interior. Since not many planets have been explored, nothing can be accurately stated for all the planets in our solar system. Proof of seismic activity has been found on the surface of Mars and Venus. Recently an earthquake of \(7\) Richter scale was recorded on the surface of Mars, and it was termed as ‘Mars Quake’.

Q.5. Can an earthquake occur underwater?
Ans: An earthquake that occurs underwater is called a submarine earthquake. Such an earthquake triggers a series of waves that results in a tsunami. These earthquakes damage the communication cables and optical fibres underwater and are most commonly observed around the Asian subcontinent.