Earthquake key facts

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Key words

The groundshaking as a result of the rocks within the earths lithopshere

hen the crust moves, there is a slow build up of stress within the rock and when it is relased it causes the ground to shake from the realease in energy through seismic waves

Epicentre - the point immediatly above the focus

Focus - The point where the pressure release in the Earth 

shallow earthquake have shallow focus - 0-7km deep causes greatest damage as energy is not dissapted - thesee account for 75% of earthquake energy released

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The distribution of eathquakes

vast majority along plate margins - most powerful being conseravtive and destructive faults

some associated with old fault lines such as the Midlands earthquake in Dudley in 2002 of 4.8 - result of movement on a old fault line called Malvern line

some human acitivty the result such as the Three Gorges Dam reservoir in China

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Measuring Earthquakes

Richter scale measures magnitude (the amount of energy)

  • Logarthermic
  • each step marks an 10x increase in amplitude in wave and 30 fold increase in energy
  • most commonly used
  • goes from 0-10

The modifiyed Mercalli  instensity scale measures intensity

  • Measures the impact /effect of the quake
  • Goes from I- X
  • Good for insurance companies - but is subjective
  • level I is detected by seisometres but felt by very few people
  • Level X is destruction with the collapse of structurs - 8.5 on the richter scale
  • based on observed effects
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Prediction of Earthquakes

There is no way of predicting exactly when an earthquake is going to happen but there are possible clues people and experts could look out for including

  • small tremors pre the major event which can be detected by seimsographs
  • strange animal behavior
  • monitoring ground water levels
  • monitoruing fault line activity
  • lookinng at past records
  • release of radion gas
  • mapping the fault
  • monitoring the earths magnetic field
  • P waves but only whilst its happened
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Prevention of earthquakes

sceinests have been looking into lubcricating fault lines to stop the build up pressue with oil and water

not sucsesful on a large scale

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Protection

Earthquake proof buildings - steel jolt joints

fire prevention

aid

government plan

education

risk areas

ensurance land use planning

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