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Earthquake Vulnerability Reduction
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The Indian sub continent is highly prone to natural disasters. Floods, droughts, cyclones and earthquakes are a recurrent phenomenon. As per the latest seismic zoning map brought out by the Bureau of Indian Standards (BIS), over 65% of the country is prone to earthquakes of intensity MSK VII or more. Some of the most intense earthquakes of the world have occurred in India, but fortunately, none of these have occurred in any of the major cities. India has highly populous cities including the national capital of New Delhi, located in zones of high seismic risk. Typically, the majority of the constructions in these cities are not earthquake resistant. Thus any earthquake striking in one of these cities would turn into a major disaster.

Six major earthquakes have struck different parts of India over a span of the last 15 years. The damages caused by these earthquakes reiterate the scale of vulnerability. However, if any of these earthquakes had struck populous urban centres, the damages in terms of human lives and property would have been colossal.

Frequent disasters lead to erosion of development gains and restricted options for the disaster victims. Physical safety-especially that of the vulnerable groups-is routinely threatened by hazards. Disasters such as the Gujarat Earthquake have very clearly illustrated that we need mitigation, preparedness and response plans so that the treat to human life and property is minimized.
The vulnerability atlas of India  published by Building Materials & Technology Promotion Council (BMTPC) of Govt. India, and  Code of Practice (IS 1893:2002, Part 1) for Earthquake Resistant Design has divided India into four zones depending on the earthquake vulnerability of the area i.e. Zone- II, III, IV, and V. Zone II is Low Damage Risk Zone, Zone-III is Moderate Damage Risk Zone, Zone –IV is High Damage Risk Zone and Zone-V is Very High Damage Risk Zone. Earthquake, which is highly unpredictable and inevitable, has rocked several parts of the country during the last few decades. But the recent one in Bhuj on Jan 26, 2001 has exposed the impact of human intervention with environment without necessary precautionary measures. Rapid industrialization and urbanization combined with population explosion have added to our vulnerability to earthquakes. All these factors have urged us to have a comprehensive earthquake mitigation strategy.

CONCEPT OF EARTHQUAKE
A brief account of terms associated with the earthquake is placed below:

»   Earthquake:  
    Earthquake is a series of ground vibration, caused due to the release of  strain energy in the form of seismic waves.
   
Focus :
    The originating earthquake source of waves inside the earth. It is also called Hypocentre.
     
»   Epicentre:
    The geographical point on the surface of the earth vertically above the focus of the earthquake.
     
»   Magnitude:
    The magnitude of earthquake is a number, which is a measure of energy released in an earthquake. Magnitude of an earthquake is always constant.
   
Intensity:

The intensity of an earthquake at a place is a measure of strength of shaking during the earthquake. Intensity is determined from effects on people, structures, and the natural environment. Intensity of an earthquake is not constant.
     
»   Richter Scale, MSK and MMI Scale
    Richter scale is used to measure the magnitude where as MSK (Medvedev S.Karmik  and Modified Mercali Intensity (MMI) scale   is used to measure the intensity.
     
»   Seismograph and seismogram
    Seismograph is the instrument, which records the earthquake.
Seismogram is the record of earthquake produced by the seismograph
     
»   As per the latest seismic zoning map, India has been divided in to four seismic Zones: Zone-II, Zone-III & Zone-IV, Zone-V
     
»   Our State comes under moderate risk zone (zone III) & low risk zone (Zone II)
     
»   The first recorded earthquake of the State was1676 AD in Balasore area and the first earthquake in which 11 fatalities informed was Berhampur Earthquake of 1897
     
»   Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
     
»   At Bhubaneswar, there is one recording station, which is being monitored by IMD.
     
»   As of now, prediction of earthquake is scientifically not possible apart from the Chinese method of watching for clues in unusual animal behaviour.
     
»   Apart from awareness and preparedness, consult a Structural Engineer/ Architect to make your house earthquake resistant.
     
»  

The chart depicting the correlation between magnitude and intensity is as follows:

Magnitude / Intensity Comparison :

Magnitude

Intensity

Description

1.0 – 3.0

I

I. Not felt except by a very few under especially favourable conditions.

3.0 – 3.9

II – III

II. Felt only by a few persons at rest, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motorcars may rock slightly. Vibrations similar to the passing of a truck. Duration estimate

4.0 – 4.9

IV – V

IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.

5.0
5.9

VI
VII

VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

6.0

VIII

VIII. Damage slight in specially designed structures considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.

IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.

X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.

XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.

XII. Damage total. Lines of sight and level are distorted. Objects thrown into the air.

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