general

• P waves are waves that can travel through all layers at an average speed of 6.1 km/s. They push and pull and can compress.
• S waves cannot travel through liquid, and only travel through the mantle and crust at an average speed of 4.1 km/s.
• S waves vibrate from side to side, the side to side movements causing the most damage to buildings as it has the shearing effect.
• Earthquakes occur as plates become stuck and stop moving, so pressure builds underneath the crust, when the pressure becomes to much the plates move with a jolt, this is an earthquake.
• Other causes of an earthquake

  • Mines
  • reservoirs as there is weight of the water on the cust
  • Old fault lines.
• Constructive plate margin earthquake

  • As convection currents diverge, pressure builds causing the plates to move apart with a jolt. This is an earthquake.
  • shallow, low magnitude
  • North American and Eurasian
  • Iceland 2008, 6.1
• Destructive plate margin earthquake

  • As convection currents converge, the pressure builds and plates move together with a jolt. The sima is subducted and the earthquake originates in the Benioff zone
  • deep focus, high magnitude
  • Pacific and Eurasian
  • Sendai , 2011 9.0
• a normal fault occurs when a plate moved downwards in the direction of the fault.
• Reverse faults occur when rocks move downwards in the opposite direction. The actual fault plane may not be visible due to slumping from high to low blocks.
• Transverse faults occurs perpendicular to a plate boundary, usually a conservative plate boundary.
• The Mercalli intensity scale is used to measure the intensity of earthquakes based on their effects and the destruction they cause. It ranges from 1 (felt by very few) to 12 (total destruction)
• The Richter scale measures the magnitude of the earthquake, it measures using a seismograph that creates a seismic trace.
• Advantages of Richter scale

  • Use to predict if there will be more earthquakes due to pre- shocks
  • compare with other earthquakes
  • globally understood
• Disadvantages of Richter scale

  • Takes a lot of training to know how to use it.
  • Expensive equipment
  • Only tells us the magnitude, not the level of damage.
• Advantages of Mercalli scale

  • Good in poor countries as no equipment is needed
  • Know where to send resources
  • easy to understand
• Disadvantages of Mercalli scale

  • Qualitative so it is based on opinions
  • Relies on the people you interview on being honest
  • Doesn't provide a warning of an earthquake
  • Cant compare to other earthquakes.
• Tsunami formation

  • Convergent plate margin
  • sial is subducted so it creates an ocean trench
  • Pressure builds to cause an earthquake, so the sial flicks up and displaces the water, causing a tsunami
  • Spreads outwards in all directions from the epicentre
  • Towards the coast, the water becomes shallow, and friction increases so this causes an increase in wave heigh and decrease in wave length, so the trough and crest increase.
  • Drawback occurs which is when water Infront of the wave is sucked back in to add to the wave heigh which can be up to 10m
  • Sendai - 9 on Richter scale.