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ISSN 2454-3063 www.ssresearcher.com 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. 23 THE JOURNAL OF SOCIAL ENVIRONMENT VOLUME IV NUMBERII APRIL 2015 ISSN 2454-3063 www.ssresearcher.com 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 24 THE JOURNAL OF SOCIAL ENVIRONMENT VOLUME IV NUMBERII APRIL 2015 ISSN 2454-3063 www.ssresearcher.com 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 25 THE JOURNAL OF SOCIAL ENVIRONMENT VOLUME IV NUMBERII APRIL 2015 ISSN 2454-3063 www.ssresearcher.com (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: 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 26 THE JOURNAL OF SOCIAL ENVIRONMENT VOLUME IV NUMBERII APRIL 2015 ISSN 2454-3063 www.ssresearcher.com 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): 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. 27 THE JOURNAL OF SOCIAL ENVIRONMENT VOLUME IV NUMBERII APRIL 2015 ISSN 2454-3063 www.ssresearcher.com 3. Derrick, E. 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