Definition of Earthquake

An earthquake is also called a quake, tremor, or tremblor. It is caused by the sudden shaking of the ground and layers. It is caused by the passage of seismic waves through the earth’s rock. Seismic waves are created in the earth’s lithosphere.

rock seismic
lithosphere of the earth

Seismic waves are created when some form of stored energy is released through the earth’s crust. It is usually when masses of rock straining against each other suddenly slip or fracture.

Earthquakes can range in size from those that cannot be felt because they are so weak. Then there are those who are violent enough to propel people and objects into the air.

Earth's and tremor
A image of tracked and known earthquakes and tremors

In the above image, it can clearly be seen that most of the tremors occur on the coastline. the chances of a tremor occurring in a land area are highly unlikely.

Causes of Earthquake

Earth’s major earthquakes happen mainly at the belts coinciding with the tectonic plates. In modern seismic maps, it shows instrumentally determined epicenters. The most important epicenter belts are the Circum-Pacific belt. It affects many populated coastal regions around the coastal region. it includes places like-New Zealand, Alaska, Japan, and more including coastal regions of North and South America. It was an estimate that around 80% of the energy presently released in earthquake comes from those whose epicenters are in these belts.

Earth’s Second belt is known alpide belt, which passes through the mediterranean region eastward through Asia and joins the Circum-Pacific Belt in the East Indies.The energy released in earthquakes from this belt is almost about 15% of the world’s total. The global seismicity distribution is best understood in terms of its rock plate tectonic setting.

Effects of Earthquake

Shaking and ground rupture

Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures.

Specific local geomorphological and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes.

This effect is called site or local amplification. It is basically due to the transfer of seismic motion from hard deep soils to soft superficial soils and rock to the effects of seismic energy focalication owing to the typical geometrical setting of the deposits.

Soil liquefaction

Soil liquefaction occurs because of the shaking, water-saturated granular material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Due to this effect rigid structures like buildings and bridges, to tilt or sink into the liquefied deposits.

Human impacts

The earthquake may cause injury and loss of life, road and bridge damage, general property damage, and the collapse of buildings. The aftermath may bring disease, lack of necessities, mental consequences such as panic attacks, depression to survivors, and higher insurance premiums.

Landslides

Earthquakes can produce slope instability leading to landslides, a major geological hazard. Landslide danger may persist while emergency personnel is attempting the rescue. Rock is dangerous

Fires

Earthquakes can cause fires by damaging electrical power or gas lines. In the event of water mains rupturing and loss of pressure. It may also become difficult to control the spread of a fire once it has started. for example, more deaths in the San Francisco earthquake were caused by fire than by the earthquake itself.

Tsunami

Tsunamis are long-wavelength, long-period sea waves produced by a sudden movement of large volumes of water. including when an earthquake occurs at sea. In the open ocean the distance between wave and crests can surpass 100 kilometers (62miles).and the wave period can vary from five minutes to one hour.

Flood

The flood may be secondary effects of earthquakes if dams are damaged. Earthquakes may cause landslips to dam rivers, Which collapse and cause floods.


Richter scale of earthquake magnitude

Magnitude
level
CategoryEffects Earthquakes
per year
Less than
1.0-2.9
MicroGenerally not
felt by people,
though
recorded on
local
More than
100,000
3.0-3.9MinorFelt by many
people; no
damage
12,000-100,000
4.0-4.9Lightfelt by all;
minor
breakage of
objects
2,000-12,000
6.0-6.9strongModerate
damage in
populated
areas
20-200
7.0-7.9Majorserious
damage
over large
areas;loss
of life
3-20
8.0-8.9GreatSevere
destruction
and loss of life
over large
areas
fewer than 3
A table representing the levels of Earthquake’s

Preparedness for the earthquake

The objective of earthquake engineering is to foresee the impact of earthquakes on buildings and other structures and to design. such structures to reduce the risk of damage. Specific retrofitting can improve existing structures by modifying their resistance to earthquakes. Earthquake insurance can provide building owners with financial protection against losses resulting from earthquakes.

Individuals can also take preparedness and steps like securing water heaters with heavy items that could injure someone. For areas near large bodies of water, earthquake preparedness encompasses the possibility of a tsunami caused by a large quake.

Prediction

Along with preparedness and Historical views the predictions are also important.

Earthquake prediction is a branch of the Science of Seismology concerned with the specification of the time, location, and magnitude of future earthquakes within stated limits.

To predict where the next earthquake will occur many methods have been developed. Despite the considerable research efforts by seismologists. Scientifically reproducible predictions cannot yet be made to a specific day or month.

~Nikshan


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