seismic hazards

• an earthquake is a build up of friction , resulting in a release of pressure
• the epicenter is the point on the earth's surface above the focus
• the focus is the place inside the earth's crust where an earthquake originates. the shallower the focus, the more destructive the earthquake needs to be
• human causes of earthquakes:

  • fracking
  • mining
  • reservoir construction
• physical causes of an earthquake:

  • plate tectonics, plate movements associated with stresses in the lithosphere
  • stresses overcome rock fractures along cracks , called faults , send seismic shockwaves through to the surface
• primary hazards of earthquakes:

  • seismic hazards
• secondary hazards of earthquakes:

  • liquefaction
  • landslides
  • tsunamis
  • fires
• 4 types of seismic waves:

  • primary / pressure waves
  • secondary / shear waves
  • surface love waves
  • rayleigh waves
• primary waves:

  • reach surface first
  • high frequency
  • travels through both mantle and core
• secondary waves:

  • half as fast as primary waves and reach surface next
  • travel ONLY through mantle
  • high frequency
• love waves:

  • slowest wave
  • causes lots of damage
  • moves from side to side
  • originates from epicentre
• rayleigh waves:

  • radiates from epicenter
  • low frequency
  • moves up and down
• secondary hazards associated with earthquakes:

  • landslides
  • liquefaction
  • tsunamis
• features of a landslide:

  • sudden shaking , causes slope failure
  • can destroy homes , roads , kill people
  • example : avalanche in Mount Everest base camp , killed 17 and injured 61
  • example: 2015 , Nepal Earthquake , 21,000 landslides occurred
• liquefaction is when soil is saturated with water , the vibrations of an earthquake causes it to act like a liquid. Soil is easer to deform and weaker , more likely to subside when it has a heavy weight on it e.g building.
• examples of liquefaction:

  • responsible for extensive damage to residential property in Christchurch , new Zealand Earthquake , 2011
• features of a tsunami:

  - long wavelength , low amplitude

  • travel at high speeds (over 700km/h)
  • shallow water and funnelling effect of bays dramatically increase height
• Tsunamis are triggered by underwater earthquakes , quakes cause seabed to move , displaces water. waves radiate out from epicenter , greater movement of seafloor , greater volume of water displaced and the bigger the wave produced
• the closer to the coast tsunami waves start , the less energy they'll lose
• primary hazards are initial impacts caused by seismic hazard
• secondary hazards occur due to primary hazards
• shallow-focus earthquakes is where the focus is 0-70km under the earths surface
• deep focus earthquakes is where the focus is 70-700km under the earth's surface.
• deep-focus earthquakes are caused by previously subducted crust moving towards the core , heating or decomposing
• deep focus earthquakes are less damaging than shallow-focus because the shock waves have to travel further and cause less shaking at the surface
• underwater earthquakes move the sea-bed , causes water to get displaced , if enough water is displaced , tsunamis happen
• underwater earthquakes can be shallow or deep focus , deeper the focus the bigger tsunami
• magnitude 9 earthquake off the coast of Tohoku , Japan resulted in a tsunami in 2011
• characteristics of tsunamis:

  • long wavelength at sea (100km)
  • short amplitude (1m)
  • tsunamis can reach speeds up to 700kph in deep water
  • hit coastlines as a wavetrain
• earthquake scales


  • richter scale
  • moment magnitude scale
  • Mercalli scale
• richter scale


  measures magnitude of earthquake through shaking - no upper limit , logarithmic
• moment magnitude scale (MMS)


  based on total amount of energy released by an earthquake - no upper limit and more accurate than Richter scale , especially for larger earthquakes
• Mercalli Scale


  measures impacts of earthquake using observations e.g reports and photos. Scale of 1 - 12 = 12 being total destruction
• what causes more landslides to occur?


  loosened ground material makes it easier for water to infiltrate , weight of water can trigger another landslide