earthquakes

• define an earthquake


  the shaking of the ground caused by sudden motions along faults or fractures in the earths crust
• define a hypocentre / focus

  point of origin of an earthquake inside an earths crust

  
  

  the focus point within the ground where the strain energy of the earthquake stored in the rock is released
• define focal length


  the distance between the hypocentre and the epicentre on the surface
• define epicentre


  the point on the Earth's surface directly above the focus/hypocenter of an earthquake
• what is the 1st in the sequence of the generation of an earthquake

  1. a gradual build up of tectonic strain
• what is the 2nd in the sequence of the generation of an earthquake

  2. the rock fractures when pressure exceeds the strength of the fault
• what is the 3rd in the sequence of the generation of an earthquake

  this results in a sudden release of energy creating seismic waves that radiate away from the point of the fracture
• what is the 4th in the sequence of the generation of an earthquake

  rebounding of the brittle crust on either side of the fracture causes the ground to shake which is felt on the surface
• characteristics of a shallow focus earthquake

  most damaging (often)

  less than 40km deep
• why are shallow focus earthquakes the most damaging (often)

  seismic waves have less distance to travel to the surface and therefore loose less energy whilst travelling to the surface
• why are shallow focus earthquakes not always most damaging

  depends on other factors eg, how built up is the area
• what are the 3 types of seismic waves

  P waves and S waves and L waves
• what are P waves

  Primary waves, the seismic waves which are the first to arrive at the crust

  
  

  have a short wave length

  moves through rock and fluids

  caused by compression - the 'shunting' effect

  
  

  not the most damaging

  faster than s waves, 8km/s
• what are S waves

  secondary waves, the seismic waves which are last to arrive at the crust

  
  

  only moves through solid rock

  longer wave length

  vibrate at right angles to the direction of travel

  
  

  causes more destruction

  slower than p waves, 4km/s
• what are L waves

  love waves

  
  

  only travel through the surface and move side to side

  
  

  most destructive

  slowest of the seismic waves
• what two characteristics are used to measure earthquakes

  magnitude

  intensity
• what is prediction of earthquakes
• what is forecasting of earthquakes
• what is magnitude


  a measure of the amount of energy at the epicentre

  - qualitative
• how is magnitude used to measure earthquakes

  moment magnitude scale is the most commonly used to measure the ammount of energy released at the epicentre, it is accurate especially for larger earthquakes

  
  

  it measures the total energy released by the earthquake at the moment it occurs: called the siesmic moment
• what does the moment magnitude scale use to measure magnitude

  for example

  -size of seismic waves

  -ammount of rock movement/slippage
• what is the range/scale of the MMS

  1-10 but it is infinite, aka it can be extended if an earthquake needs

  
  

  it uses a logarithmic scale
• what is a logarithmic scale

  each increase on a scale is an increased magnitude of x10
• what is intensity


  the ammount of ground shaking and damage caused by an earthquake

  - more subjective
• what is the relation ship between magnitude and frequency

  inversely proportional
• what is a seismometer


  a device which measures the amount of ground shaking

  
  

  it records both the vertical and horizontal movements of the ground
• what does a seismometer produce

  a seismogram

  (essentially a peice of paper that shows the data)
• what is an earthquake swam

  a sequence of seismic events occurring in a local area within a relatively short period

  
  

  aka:

  foreshock, earthquake, aftershock
• what does the modified mercalli scale measure

  intensity

  
  

  subjective (what you can feel and see eg how scared people are, how much destruction there is)
• what is the modified mercalli scale marked in

  by roman numerals I - XII

  
  

  the higher numbers are usually based on observed damage and lower numbers are based on what people feel