ADVERTISEMENTS:
Here is a compilation of essays on ‘Earthquake’ for class 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Earthquake’ especially written for school and college students.
Essay on Earthquake
Essay Contents:
- Essay on Introduction to Earthquake
- Essay on the Causes of Earthquake
- Essay on the Distribution of Earthquakes
- Essay on the Prediction of Earthquakes
- Essay on the Facts about Earthquakes
- Essay on the Classification of Earthquakes
- Essay on the Record of Earthquakes
- Essay on the Seismic Waves Produced during Earthquake
- Essay on the Earthquakes Resisting Structures
- Essay on the Effects of Earthquake
Essay # 1. Introduction to Earthquake:
ADVERTISEMENTS:
We know that various forces of nature are responsible for changes in the crust of the earth. Earthquake is a movement of tremor of the earth’s crust. It originates naturally and below the surface. It sometimes causes a permanent change of level at the surface of the earth.
The place of origin of an earthquake below the earth’s surface is called the centre. The point on the surface vertically above it is known as the epicentre. The intensity of tremor is at the maximum near this epicentre.
It is known from Seismograph that the vibrations spread in all directions from the point of origin of an earthquake. These vibrations can be compared with the series of concentric waves of water generated by a stone when thrown into a still pond.
The earthquake waves are of three types:
ADVERTISEMENTS:
(а) Primary waves (P):
These are longitudinal waves. They move faster through solid and speeds slow down when they pass through liquid.
(b) Secondary waves (S):
These are like light waves where particles move perpendicular to the wave. They can travel through solid only and disappear in liquid.
ADVERTISEMENTS:
(c) Long waves or Surface waves (L):
These waves affect only the surface of the earth and dies out at smaller depth. They are violent and most destructive.
The earthquake tremors are of two types: vertical and horizontal. The intensity of vibration is more at the epicentre because the tremors move vertically to it. Its intensity is less when the vibrations spread in horizontal direction outside the epicentre.
The vibrations may be mild or strong. Generally the mild or minor earthquakes occur more frequently than the strong or major ones. Usually the greatest amount of destruction is felt near the epicentre.
Essay # 2. Causes of Earthquake:
There are many causes for earthquakes. Among them tectonic movement of the earth, volcanic eruption, icefall and landslide are the main ones.
Tectonic Movement:
The material of the interior of the earth gradually contract due to loss of heat by radiation. As a result of this, some tectonic forces (tensional and compressional forces) are produced which shake the surface. These forces are mainly responsible for the formation of Fold Mountains and rift valleys. That is why, the earthquakes occur more frequently in the regions of Fold Mountain.
Volcanic Eruption:
ADVERTISEMENTS:
During volcanic eruptions lava, ashes and steams come out with an enormous force. These cause earthquakes on the surrounding areas of the volcano.
Icefall:
Sometimes large blocks of ice fall into the valleys from a snow capped mountain. Such a fall may cause a minor earthquake.
Landslide:
In mining area sometimes a large portion of land falls into the vacant space below and causes earthquake of minor nature.
The other causes of earthquakes may be due to the various reasons depending upon their intensity.
The following are the major causes:
i. Superficial movements.
ii. Volcanic eruption.
iii. Faulting and folding.
iv. Earthquakes due to other causes.
Earthquakes due to superficial movements:
The feeble earthquakes are caused due to the superficial movements such as dynamic agencies operating upon the earth’s surface.
Examples:
(i) The dashing of waves cause vibration along seashore.
(ii) Water descending along high waterfalls.
(iii) The snow falling (avalanche) down from high altitude causes ground vibration.
(iv) The movement of locomotive and working of heavy machinery produces feeble vibration, along the railway tracks and in industrial areas.
Earthquakes caused due to volcanic eruption:
Some of the volcanoes may also produce earthquakes such earthquakes are generally feeble or severe.
Earthquakes caused due to folding and faulting:
The earthquakes caused due to folding/faulting are more disastrous. They are known as tectonic earthquakes and directly or indirectly change the very structural features of the earth’s crust.
Earthquakes caused due to other causes:
Atomic minerals disintegrate emanating α (alpha), β (beta), ϒ (gamma) rays due to radioactivity or due to bombarding. This produces enormous amount of heat and energy within the crust of the earth, which may also initiate very severe earthquakes.
Atomic tests:
Atomic tests conducted in earth’s crust or oceans, which have become a common thing now-a-days, release enormous energy on account of sudden explosion, which follows initiation of earthquakes.
Rocks burst and blasting in the deep under mines generally initiates earthquake tremors.
Essay # 3. Distribution of Earthquakes:
With the help of Seismograph nearly 8-10 thousand earthquakes are recorded yearly on the surface of the earth. That is, one in every hour. It has also been verified that all the earthquakes originate within 50-100 km of the earth’s crust. The earthquake waves radiate in all directions from the centre of origin.
Although earthquakes occur in almost all regions of the earth, they are mainly confined to two well defined belts:
(а) The Circum-Pacific Belt:
This belt is associated with the Circum-Pacific belt of mountain, i.e., the Rockies, Andes, etc., fold mountains, west coast of Japan, Philippines, Indonesia and other island groups along the eastern coast of Asia. Nearly 68 per cent of the earthquakes of the world occur here.
(b) The Mid-World Mountain Belt:
It follows the mountains bordering the Mediterranean Sea, Alps, Caucasus and the Himalayas. Nearly 21 per cent of the earthquakes of the world originate in this belt.
The earthquakes occur in geologically active areas, mid oceanic ridges and mountain building regions. The zones where earthquakes occur frequently are known as seismic belts.
The principal seismic belts on the earth’s surface are as follows:
1. The circumpacific belt:
The belt encircles the Pacific Ocean and more or less overlaps the belt of young mountains and the zone of active volcanoes. This belt covers Chile, Peru, Central America, Caribbean area, Mexico, Kamchatka, Japan, Philippines, Indonesia, New Zealand, etc.
2. Alpine Himalayan belt:
The belt starts from East Indies and passes through the Himalayan foothills region to the Alpine mountain areas of Europe, rift valley of east of North Africa, Spain, Italy, Greece, Turkey, Iran, North India and Burma.
In India, earthquakes frequently occur along the foothill zone of Himalayas beginning from Kashmir in the west to Assam in the east. After 1819, about 15 very destructive earthquakes have occurred in India.
Some of the earthquakes are as follows:
1. Assam 1819, 1897 and 1950. Intensity 8.5 and it is Catastrophic of the world.
2. Bihar 1934 and 1992 Uttarkashi (North Bihar).
3. Indo-Nepal Border, 1988.
4. Himachal Pradesh 1905, 1975 and 1987.
5. Kashmir 1963, 1972 and 1976.
6. Kuchchh area, Gujarat 1819, 1956, 1970 and 2000.
7. Lathore, Maharashtra 1993.
8. Gujarat (Republic day, 2001)
Essay # 4. Prediction of Earthquakes:
The precise prediction about earthquake calamity is elusive though it is not impossible, since for human grey matter sky is the limit. Recently, the frequency of earthquake calamities in the region has attracted the attention of the scientists all over the world.
It has been observed that earthquake may occur and reoccur at the same places and new places but they do not have any regular scale or frequency. The scientists know that elastic strain is piling up along SAF (San Andreas Fault) since 1906, but they are unable to forecast the exact day, time and place.
In about half of the cases, just before the rocks reach the rupture point to announce the event, small foreshocks announce hours, days or even months before the climax shock, that stress has become critical. The long series of post event tremors indicate adjustments.
Sometimes, the break may be as large as the major shock. Unusual animal behaviour, fluctuations of ground water level in wells and springs and variation in the discharge of springs are the phenomena closely related to the development of fractures.
In China, about 90 per cent of the country is lying on the young and restless crust. Chinese have successfully employed most of the precursors in predicting major disasters and have specially mastered the art of closely monitoring and analysing normal behaviour of animals to forecast earthquakes.
The Haicheng earthquake of February 1975, of 7.3 magnitude, destroyed 90 per cent of the structures, but without loss of life due to timely evacuation of the population of nearly a million. There is evidence that full moon and associated high tides, excessive precipitation and sharp biometric gradient changes, and particularly another quake elsewhere act as ‘trigger’ for earthquake.
Essay # 5. Facts about Earthquakes:
I. Earthquakes do not kill people, structurally unsound buildings can do.
II. There is no foolproof mechanism or technology in the world to predict quakes.
III. Himalayas could be ‘overdue’ for a great earthquake, though no one knows when and where these will occur.
IV. Active thrust faults exist all across foothills of northern India, the north-east and into northern Pakistan.
V. The subcontinent is sitting on the highly seismic Indian plate, with some major fault lines. In fact, there is no safe zone in India.
VI. Of late, the Indian plate boundary has become very active. It is on gradual move, pushing against the Eurasian plate by 4-5cm every year.
VII. All the plates of India should have a disaster management authority to deal with any eventuality.
VIII. Building of laws formulated after 2001 Bhuj earthquake to ensure the construction of quake-proof houses have not been implemented by any state government.
IX. India is among the few countries with no regulatory mechanism to control building activities.
X. Tremors of the Muzzafarbad quake were felt as far as west Bengal.
XI. Disasters have left the 800 years old Qutub Minar with slight tilt, but it has survived several quakes in its life time.
Essay # 6. Classification of Earthquakes:
The earthquakes are classified on number of bases. Of these the depth of FOCUS, the cause, the intensity and magnitude of earthquakes are very important.
1. Classification based on depth of Focus:
Accordingly the earthquakes are termed as:
i. Shallow:
When the focus lies within 60 km.
ii. Intermediate:
When its focus lies within 60 to 300 km from the surface.
iii. Deep seated:
When the focus lies beyond the 300 km depth.
2. Classification based on origin:
The earthquakes are broadly classified into Tectonic and Non- Tectonic types. The tectonic earthquakes are directly related to the movements of crystal block along faults. They are generally very severe and area affected is often very great.
The non-tectonic type includes earthquakes due to number of causes such as:
i. Volcanic eruptions.
ii. Collapse of underground caverns.
iii. Superficial movement like landslides, etc.
3. A third way to classify the earthquakes is on the basis of their intensity, which is defined by the effects or degree of damage that an earthquake produces on the structure and features of the earth.
A numbers of scales of intensity have been suggested.
Some of them are:
i. Rossifeerets scale, and
ii. Mercale scale.
Richter’s scale:
This scale of intensity is adopted internationally. Charles F. Richter, an American Seismologist, devised the earthquake intensity scale. This is based in the total amount of energy released during an earthquake. The energy is called ‘magnitude’. The magnitude is calculated mathematically using the amount and duration of ground vibration/tremors as recorded by seismograph.
Essay # 7. Record of Earthquakes:
Seismograph:
The instrument used for recording the vibrations of the earth crust is known as ‘seismograph’.
The vibrations are recorded on a strip of paper or photograph film and the diagram is produced as shown:
Most seismographs contain a heavy weight suspended from a support, which is attached to bedrock. When waves from a distant earthquake reach the instrument the inertia of the weight keeps it stationary while the earth and support vibrate.
The movement of the earth in relation to the stationary weight is recorded on a rotating drum. Some seismographs detect horizontal motion while others detect vertical motion. The traces of the earthquake waves are usually recorded on a moving photographic paper as a series of zigzag lines.
With the help of seismograph the distance between the recording station and the epicentre is located or determined.
Essay # 8. Seismic Waves Produced during Earthquake:
At the time of earthquake three types of waves are produced from the focus Seismic waves are of three types—P waves, S waves and L waves.
Surface waves or L waves are responsible for causing earthquakes while the importance P and S waves are in study of earth’s interior. P and S waves travel through the interior of the earth and are reflected and refracted as they enter core and mantle layers.
P waves or Primary waves:
These are compressional waves, which cause the material of rock to vibrate in longitudinal direction. The primary waves travel faster, therefore, they reach the seismic station first.
They pass through solid as well as liquid media. The velocity of P waves from 5.5 to 13 km per second. These waves are also called as Push waves and are similar to Sound waves.
S waves or Secondary waves:
These are shear waves, which are transverse in nature, whose velocity is less than P waves. (The velocity of these waves varies from 3 to 7 km per second). The S waves travel through solids only and do not pass through liquid media.
L waves or Surface waves:
When primary and secondary waves reach the earth’s surface they are converted into longitudinal wave. L waves travel along the surface and cause earthquakes. They are traverse in nature and their velocity is much less than P and S waves (velocity varies from 4 km to 4.3 km per second.
Essay # 9. Earthquakes Resisting Structures:
To build earthquake-resisting structure it is very essential to determine the probable intensity and magnitude in the concerned area. The history and record of previous earthquake and the knowledge of geology of the area are helpful in this connection.
i. Perfectly designed steel framed or reinforced ferro concrete structure possesses high degree of resistance from damage.
ii. It is recommended that in soft grounds where soil-bearing capacity is very poor, a concrete raft- foundation should be adopted for structures.
iii. The height of large building should not exceed 100 ft. The heavy loads near the top, like heavy stone work in coping and water tanks should be avoided.
iv. Bridges with screw pile foundation stand better to the shocks, than that of bridges with brick arches, and girder supported on stone work piers.
v. In house construction light roof (Low density concrete) and polymer construction material are recommended.
vi. Walls constructed in cement with wet bricks work bonded are essential.
vii. Careful planning can ensure that the streets are wide in relation to the height of buildings. Many of the deaths caused during earthquakes are due to the collapse of tall buildings into narrow streets.
viii. Reinforced concrete houses are relatively stable. Doors and windows are provided in alternate positions.
ix. The most secure house is one that will move as a unit.
x. The light weight material such as wood, hard board and light weight fire proof polymer products are employed in the construction of residential building particularly in strong seismic zones as found in Japan.
xi. The main aim of the engineer is to design and construct buildings, bridges and dams in seismic zones considering seismic co-efficient of the locality in such a way that they can minimise loss of life during an earthquake.
Essay # 10. Effects of Earthquake:
1. In cities seismic waves disrupt underground service such as water, gas pipelines, bursts causing fire.
2. Roads are fissured, railway lines are twisted, dams and bridges are destroyed, electrical transmission is snapped causing short circuit of electricity and out-break of fire hazards.
3. Buildings are damaged and people get frightened resulting in loss of life and property.
4. Permanent tilting of landmass may occur in certain areas, landslides may occur in hill regions.
5. Rivers change their courses; fissures are opened up in the ground, which may cause springs.
6. Earthquakes occurring below the ocean floor may cause heavy damage to coastal areas.
Various changes take place on the surface of the earth as a result of earthquake. Some areas may subside or rise-up due to earthquakes. The earthquakes may also bring about a change in surface drainage by causing landslides and damming of rivers. This leads to flood or formation of lakes in the upper reaches of the rivers.
Sometimes large areas may be raised up above sea level so that they become plains. Sometimes again, a large plain may sink and become part of a sea. Sedimentary rock layers may be folded by the pressure exerted by the earthquakes. Devastating sea waves are also caused by the earth tremors.
They often cause great loss to the coastal areas. Although earthquakes are generally disastrous, they sometimes do constructional work also. They can create lakes, plains and islands.
The earthquakes of Bihar (1903 and 1934), of Baluchistan (1935), of Tokyo (1923), of Assam (1897 and 1950) and recent earthquakes of Chile, Mexico, Yugoslavia and Iran caused great loss to human lives and property, and brought about many changes to the earth’s surface.
The recent earthquakes of Armenia (1988), Turkey (1999), India (2001), Pakistan-India (2005) and of Iran (1989, 2006) are also worth mentioning. Recently, the earthquake of March 11, 2011 of Japan has completely destroyed the city of FUKUSHIMA and also 4 nuclear reactors.