GENERAL INFORMATION ABOUT EARTHQUAKES AND SAFETY MEASURES

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Earthquakes

Earthquake and its causes

  • An earthquake is a series of vibrations on the earth's surface caused by the  generation of  elastic  (seismic) waves due to sudden  rupture  within the earth  during  release of  accumulated  strain  energy.

  • Faulting  may be  considered as an immediate  cause of an earthquake.    Due to constant  movement of plates,  deformation is caused which  results  to generations of strain  energy. 

  • Indian  plate is moving in  north-north-east  direction  and  colliding  with  Eurasian  plate   along  the  Himalayas.

DEFINITIONS

  • EPICENTRE:  It  is  the point on the (free)  surface of the earth vertically  above the  origin    place  (hypocentre)  of an earthquake.   This point  is expressed  by geographical  latitude  and longitude. 

  • MAGNITUDE :  It is  a quantity  to   measure the size of an earthquake  in terms of its  energy  and is independent  of the  place of  observation. 

  • RICHTER  SCALE :  Magnitude  is measured  on the  basis of  ground  motion  recorded  by an instrument and  applying  standard  correction  for the epicentral  distance from  recording  station. It is  related with the  logarithm  of amount  of energy  released by an  earthquake  and  expressed  in  Richter  Scale. 

  • INTENSITY:  It  is the rating  of the effect of an earthquake at a particular   place,   based on the observations of the damaged  areas,   using a descriptive  scale  like  Modified  Mercalli  Scale.

CLASSIFICATION OF EARTHQUAKES

  • Slight              :  Magnitude  up to   4.9  on the  Richter  scale

  •  Moderate        :  Magnitude   5.0   to  6.9

  • Great               :  Magnitude  7.0  to  7.9

  • Very  great      :  Magnitude  8.0  and  more

EARTHQUAKE   MONITORING

India   Meteorological  Department  (IMD)  is the  national  agency  for  detecting  and  locating  earthquakes  and  evaluation  of  seismicity  in  different  parts of  the  country.

EARTHQUAKE   PREDICTION

Earthquake  prediction  is not  yet  scientifically  possible with   reasonable  accuracy in  terms of   location,   time  and  magnitude.  

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Some Do's and Don'ts

DO's

  • Take  shelter under a desk, table,  bed   or  doorway  during an earthquake.

  • Provide help to others  and develop  confidence. 

  • Shut  off  kitchen gas. 

  • Keep stock of drinking water,  food  stuff and  first aid arrangements.         

  • If  you  are in a moving  vehicle,  stop and stay in vehicle. 

  • Follow and  advocate local  safety  building code for  earthquake resistant  construction. 

  • Heavy objects,  glasses  should be kept on  lower  shelf. 

  • Turn on transistor  or  T.V.  to get  latest information. 

  • Make plan and  preparation  for emergency  relief.

DON'Ts

  • Do  not  get  panicky

  • Do not use candles,  matches  etc  and  do not  switch o  any electric  mains  immediately  after an earthquake.

  • Do not spread and  believe in  rumours

  • Do not run through or near buildings during an  earthquake

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Seismic zoning in India

Seismic zoning map of a country is a guide  to   seismic  status  of a region  and its  susceptibility  to  earthquakes.    India has been divided  into  five  seismic  zones with  respect  to severity of  earthquakes.    Of   these   Zone  V is the  seismically  most  active  region  where earthquakes  of   magnitude  8 or more  could oocur.   Zone I  is the seismically   least  active  region.

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Network of Seismological Observatories in India

India   Meteorological Department (IMD)  operates a network of  seismological observatories spread all over the country. There are 45  national  seismological  stations and  13 special  purpose observatories. The first  seismological  observatory  was established by  IMD at  Calcutta in as early  as 1898. The network  is being  strengthened and  modernised and  during  1996-97  ten  observatories  have been  upgraded  to  the  standards of  Global  Seismograph  Network (GSN).

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