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THE INTENSITY OF EARTHQUAKE IN INDIA
MS.RAMESH SARKAR
ASSISTANT TEACHER
BHATIBARI HIGH SCHOOL
BHATIBARI
ALIPURDUAR
WEST BENGAL
ABSTRACT
An earthquake is a major demonstration of the power of the tectonic forces caused by endogenetic
thermal condition of the interior of the earth. ‘An earthquake is a motion of the ground surface, ranging
from a faint tremor to a wild motion capable of shaking building apart and causing gaping fissures to open
in the ground . the earthquake is a form of energy of wave motion transmitted through the surface layer of
the earth in widening circles from a point of sudden energy release, the ‘focus’ (A.N Strahler and A.H
Strahler, 1976). The magnitude or intensity of energy released by an earthquake is measured the Richter
scale devised by Charles F. richter in 1935. The number indicating magnitude or intensly (M) on Richter
scale ranges 0 and 9 but in fact the scale has on supper limited of number because it is a logarithmic scale.
‘it is estimated that the total annual energy released by all earthquake is about 1025ergs,and most of this is
from a small number of earthquake of magnitude over 7’ (A.N. Strahler and A.H. Starhler, 1976). The
1934 Bihar earthquake (India) measuring 8.4 magnitude on Richter scale and good Friday earthquake of
march 27,1964,in Alaska, U.S.A. measuring 8.4 to 8.6 on Richter scale are among the greatest earthquake
of the world ever recorded. The following description of Richter scale may help in assessing the
devastation caused by the energy releases during earthquake of varying magnitudes. ‘the world’s largest
and most intensive recorded earthquake was of the magnitude of 8.9 (and 9.3) and the number of recorded
earthquakes increases 10 times as magnitude decreases by one.’
TABLE I: RICHTER SCALE OF EARTHQUAKE MAGNITUDE
Magnitude
0
2.5 to 3.0
4.5
5.0
6.0
>6.0
Description
Smallest earth tremor detected by seismography only. Energy released by
such insignificant earthquake amount to 3 x 1012 ergs.
Such earthquake may be fell and detected if they occur near the settlements.
The annual frequency of such earthquake is around 100,000. No damage is
done.
Local damage is done.
The quake is this magnitude equal in energy to ordinary atomic bomb. The
atomic bomb hurled on Hiroshima (Japan) during Second World War equaled
the magnitude of 5.7 on Richter scale. The energy released from such
earthquakes equals 8 x 1020 ergs.
Such earthquake become destructive within a limited area provided that the
geological structure is weak and the are is heavily populated.
Devastation increases with increasing magnitude.
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Another scale of the measurement of the degree of destructiveness or intensity of earthquake is Mercalli
scale. The degree of destructiveness or intensity of an earthquake depend on a verity of factors e.g.
magnitude, distance from epicenter, acceleration, duration, amplitude of waves, type of ground, water
table, natural of geomaterials of the region concerned and the nature and type of construction (such as
buildings made of wood or bricks or stones or concretes, dams weather concrete or earthen, duildings
made of muds, tin shades, huts etc.) affected by an earthquake. Table 18.3 represents the contrive picture
of mercalli Intencity Scale and richter Magnitude Scale.
TABLE II : COMPARATIVE PICTURE OF MERCALLI OF RICHTER SCALE
Mercalli intensity
I
Description of Characteristic Effects
Richter Magnitude
corresponding
to
highest
intensity
reached
Instrumental
The tremors of this category earthquakes are detected
only by seismographs
II
Feeble
Such earthquake are notice by only sensitive people
III Slight
Like the vibrations coused by passing truck or lorry: felt
by people at rest especially in upper floors of buildings
Iv Moderate
Felt by people while walking; rocking of loose objects
including standing vechicles
V
Rather Strong Felt generally most sleeping people are qwakend and
bells ring
VI Strong
Trees sway and all suspended object s swing damage is
caused by overturning of vehicles and falling of losse
objects
VII Very Strong General alarm walls crack plaster falls
VIII Destructive
Vehicle divers seriously disturbed masonry construction
are fissured, chimneys fall poorly constructed buildings
damaged
IX
Ruinous
Some houses callapes where ground begins to crack and
pipes breack open
X
Disastrous
Ground cracks badly manybuilding destroyed and
railway lines bent landslides an steep slopes
XI
very Few buildings remain standing bridges destroyed all
disastrous
serivces (railways, pipes and cables) out of action great
landslides and floods
XII Catastrophic Total destruction; objects thrown into air; ground rises
and falls in waves.
3.5
4.2
4.3
4.8
4.9-5.4
5.5-6.1
6.2
6.9
7-7.3
7.4-8.1
About 8.1
The place of the origin of an earthquake is called focus which is always hidden inside the earth but
the depth of which varies from place to place. The deepest earthquake may have its focus at a depth
of even 700 km below the ground surface but some of the major Himalayan earthquakes, such as the
Bihar-Nepal earthquake of August 21, 1988, have their focus around 20-30 km deep. The place on
the ground surface, which is perpendicular to the buried ‘focus’ or ‘hypocenter’, recording the
seismic waves for the first time is called epicenter. The seismic waves move away from the source of
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the earthquake (focus or hypocenter) in the form of (i) primary or pressure waves (P waves), (ii)
secondary, shear or transverse waves (S waves) and (iii) long waves or surface waves (L waves).
These seismic waves recorded with the help of an instrument called seismograph or seismometer at
the epicenter. The patterns of recorded seismic waves are studied and various definite information
about the center of the origin of the earthquake (focus or hypocenter), magnitude and destructive
power of the earthquake, probable cause of the earthquake etc. are received.
CAUSED OF EARTHQUAKES
Earthquakes are caused due to disequilibrium in any part of the crust of the earth. A number of caused
have been assigned to cause disequilibrium in the earth’s crust such as volcanic eruption, faulting and
folding, up warping and down warping, hydrostatic pressure of man-made water bodies like reservoirs
and likes, and of late the plate movements. The occurrence of severe devasting earthquakes of San
Fransisco (U.S.A) in 1906 led H.F. Ried, one of the official investigators of San Fransisco earthquake
disaster, to advance his important ‘elastic rebound theory’ to explain the mode and causes of earthquakes
mainly cased by fractures and faults in the earth’s crust and upper mantle. Recently, ‘plate tectonic
theory’ has been accepted as the most plausible explanation of earthquakes. As per theory of the plate
tectonic the crust of the earth is composed of solid and moving plates having either continental crust or
oceanic crust or even both continental-oceanic crust. The earth’s crust consists of 6 major plates (Eurasian
plate, American plate, African plate, Indian plate, Pacific plate and Antarctic plate) and 20 major plates.
These plates are constantly moving in relation to each other due to thermal convective currents
originating deep within the earth. Thus all the tectonic events take place along the margins of plates.
From the standpoint of movement and tectonic events and creation and destruction of geomaterials the
plate boundaries are divided into 3 types.
1. Constructive plate boundaries : are characterized by continuous addition of geomaterials as
there is constant upwelling of molten materials from below along the mid-oceanic ridges.
These molten hot materials (lavas) are cooled and solidified and are added to the trailing
margins of the divergent plates. In fact, divergent plates move in opposite directions from
the mid-oceanic ridges and there is always addition of new crust to the trailing ends of these
plates because of cooling and solidification of , olden lava.
2. Destructive plate boundaries: are those where two convergent plates collide against each
other and the heavier plate boundary is sub ducted below relatively lighter plate boundary.
This results in constant loss of crustal materials.
3. Conservative plate boundaries: are those where two plates pass past each other without any
collision. This process results in the creation nor in the creation nor in the destruction of
crust.
EARTHQUAKE HAZARDS IN INDIA
India is frequently adversely affected by moderate to severe earthquakes in different parts of the country
mainly the Himalayan regions, north Bihar, N.E. India, Gujarat etc. after first shocking earthquakes of
Koyna in 1967 in Maharashtra, India has been severely rocked in August, 1988 (Darbhanga quake, 6.7),
October 1991 (Uttarkashi, Uttarakhand, 6.6) September 1993 (Lattur, Maharashtra,6.3), may, 1997
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(Jabalpur, M.P., 6.0), March, 1999 (Chamoli, Uttarakhand 6.8), January, 2001 (Bhuj, Gujarat, 8.1) etc.
(table 18.9)
On the basis of magnitude of damage risk India is divided into five damage risk zone as follows:
1) Zone I of least damage risk includes the places of some parts of Punjab and Haryana, plain areas
of Uttar Pradesh, portions of plains of north Bihar and west Bengal, delta areas of Godavari,
coastal plain areas of Maharashtra and Kerala, desert areas of Rajasthan and most areas of Gujarat
expect Kutch region.
2) Zone II of low damage risk includes southern Punjab and Haryana, southern parts of plains of
Uttar Pradesh, eastern Rajasthan, coastal districts of Orissa, Tamil Nadu etc.
3) Zone III of moderate damage risk represents the areas of southern and south-eastern Rajasthan,
most of Madhya Pradesh, Maharashtra and Karnataka, southern Bihar, Northern and Northwestern Orissa etc.
4) Zone of high damage risk covers Jammu and Kashmir, Himachal Pradesh, northern Punjab, and
Haryana, Delhi, western Uttar Pradesh, ‘tarai’ and ‘bhabar’ region and Himalayan regions of
Uttarakhand and Bihar, and Sikkim areas.
5) Zone of very high damage risk includes parts of Jammu and Kashmir, some parts of Himachal
Pradesh, Uttarakhand, extreme north Bihar, entire north-eastern India and Kutch region of
Gujarat.
Though the plains of west Bengal comes under the zone of last damage risk but the devastating sever
earthquake of Kolkata of 11 October, 1737 killing 300,000 people put a question mark against this
concept. The zone of very high damage risk of Kutch region of Gujarat registered most devastating killer
earthquake on January 26, 2001 (8.1 on Richter scale) in its seismic history of past 182 years killing
50,000 to 100,000 people. The towns of Bhuj, Anjar and Bhachau were flattened and razed to the ground.
MANAGEMENT OF EARTHQUAKE DISASTER
The overall management of earthquake disaster involves the following aspects:

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Risk assessment and analysis of earthquake hazards,
Preparation of earthquake vulnerability and risk zones maps,
Prediction of occurrence of earthquakes,
Earthquake disaster preparedness,
Search and rescuer operation,
Relief operation after the occurrence of earthquake disaster,
Recovery of disaster-affected people from mental, economic and social problems,
Rehabilitation of displaced people, etc.
The advanced techniques of computing facility provided by advanced computers and analysis of mass
dataset of seismic situation and geological formation provide by remote sensing technique have enabled
the experts to prepare the maps of earthquake vulnerability and risk zones of varying magnitudes. For
example, India has been divided into five earthquake risk zones (see preceding subsection, ‘earthquake
hazard in India’). All these help in making assessment of vulnerability of a region for seismic events and
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to initiate the necessary steps for the mitigation and prevention of adverse affects of seismic disasters. It
may be mentioned that the occurrences of earthquakes cannot be precisely predicted because till now no
suitable technique for earthquake prediction could be developed as the seismic events are sudden and very
rapid on-set disasters and are related to the interior of the earth about which we do not know precisely.
Though there is precursor tremors before the final on-set of earthquake disaster in near future but it is not
precisely know as to when and where the earthquake would finally strike? Inspite of the complete
uncertainty of earthquake prediction some precautionary measures, as mentioned below, should be taken
to avoid and mitigate the disastrous effects of seismic events. Such measures are related to pre-disaster
phase (see previous chapter):
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To avoid the human settlements in the high earthquake risk zone,
To follow earthquake architectural designs for the construction of buildings,
To use building materials of high quality and strength,
To stop the construction of high risk buildings in earthquake-prone areas,
To restrict the ground water mining to avoid larger cavities below the ground surface which
may weaken the foundation of buildings,
To acquaint the people of earthquake-prone areas with safety measures in case of sudden
occurrence of an earthquake, so that they can immediately follow the safety rules in the cas
of calamity,
To restrict urban growth in the hilly areas having high earthquake vulnerability risk,
To avoid the construction of large dams and reservoirs in high seismic zone inorder to restrict
the onset of reservoir-induced seismisity (RIS),
To stop deforestation and massive quarrying in the high seismic zones of hill regions, etc.
CONCLUSION
As stated earlier, it is not the magnitude of earthquake which kills people; rather it is the buildings which
kill people. So, topmost priority should be given to follow approved standards of building construction.
After the disastrous earth-quake of Bhuj (Gujarat) in 2001, the center and all the state governments of
India issued strict orders not to approve any plan for the construction of high-rise building unless the
provisions of all the safety measures as per standard codes of building construction have been taken care
but soon after the tragedy was over the people and officials became reluctant towards the implementation
of building codes and rules.
REFERENCES
1. Davies, B. E. and Pincent, R.J.F.H., 1975: Minerals and morbidity, Cambria, Vol. 2,
pp. 85-93.
2. Denevan, W. M., 1967: Livestock numbers in ninetieth-century New Mexico and the
problem of gulling in the south-west, Ann. Assoc. Amer. Geogr., Vol. 57, pp. 691-703.
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3. Derrick, E. H., 1965: The seasonal variation in Asthma in Brisbane; its relation to
temperature and humidity, Intnl. J. Biomet, Vol. 9, pp. 239-53.
4. Derrick, E. H., 1966: The seasonal variation in Asthma in Brisbane; its relation to
weather, Internl. J. Biomet, Vol. 10, pp. 91-9.
5. Dobzhansky, T., 1950: Evolution in the tropics, American Scientist, Vol. 38, pp. 20921.
6. Ehrenfeld, D. W., 1970: biological Conservation, Hold, Rinehart and Winston, New
York.
7. Elenberg, H. and Mueller-Dombis, D., 1967: Tentative physiognomic-ecological
classification of plant formation of the earth, Ber. Geobot. Forsch. Inst. Rubel, Vol.
37, p. 21-55.
8. Elton, C. S., 1927: Animal Ecology, University of Washington Press, Washington.
9. Eltobn, C. S., 1958: The Ecology of Invasion by Plants and Animals, Methuen,
London.
1. Cole, M., 1971: Plants, animals and environment, Geographical Magazine, Vol. 44, pp.
230-1.
2. Crabtree, K. and Malt by, E. M., 1975: Soil and land use change on Exmore,
significance of buried profile on Exmore, Proc. Somerset Archeol. Nat. hist. soc., Vol.
119, pp. 38-43.
3. Davies, B. E. and Pincent, R.J.F.H., 1975: Minerals and morbidity, Cambria, Vol. 2,
pp. 85-93.
4. Denevan, W. M., 1967: Livestock numbers in ninetieth-century New Mexico and the
problem of gulling in the south-west, Ann. Assoc. Amer. Geogr., Vol. 57, pp. 691-703.
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