Earthquakes

• Earthquakes- built up pressure over time is released causing shockwaves
• Shockwaves- waves of energy that travel outwards from the point of impact; either Body waves or Surface waves
• Body waves- a seismic wave that moves through the interior of the earth
• P-waves:

  • body waves
  • fastest seismic waves
  • can move through solids and liquids
  • transverse (compressional)
• S-waves:

  • body waves
  • slower than P waves
  • can only move through solids
  • longitudinal- rock particles perpendicular to direction wave is travelling
• Surface waves- seismic wave near the earth’s surface, almost entirely responsible for damage, come after body waves
• Love waves:

  • surface wave
  • fastest surface wave
  • moves ground side-to-side
  • produce entirely horizontal motion
• Rayleigh waves:

  • surface wave
  • rolls along the ground moving it up, down and side-to-side
  • causes most shaking
• Richter scale- measures magnitude, logarithmic
• Moment Magnitude Scale (MMS)- based on total amount of energy released, logarithmic
• Mercalli scale- measures impacts using observations, between 1-12
• Ground shaking- varys due to topography and physical geography (e.g. Chile 1960, largest ever 9.5)
• Faulting: the production of a fault or faults in a rock formation (e.g. Taiwan 1999, land dropped 6m and created waterfall)
• Fire- power lines knocked down, gas lines rupture (e.g. Kobe 1995, morning, people making breakfast, 300 fires took 2 days to put out, destroyed traditional wooden buildings)
• Landslides- shaking dislodges sediment, can also cause loosening of ground material allowing for water to infiltrate and weigh down sediment (e.g. Nepal on Everest)
• Tsunami- larges waves caused by the displacement of large volumes of water due to underwater earthquakes (e.g. 2004 Boxing Day Tsunami, 800km/hr, 15m high at shore, 13 countries effected)
• Liquefaction- when soil is saturated with water, the vibrations cause it to act like a liquid (e.g. Mexico City 1985, building foundations became unstable and slopes became vulnerable to mass movement)
• Distribution:

  • coincide with major plate margins
  • earthquakes at destructive margins have greater spread therefore affect more places
• Mid-plate earthquakes happen due to:

  • re-activated old faults due to mining
  • altering underground pressures due to water/ oil abstraction
• Population density- 70/100 of the largest cities (10% of the world’s population) lie in at risk zones on the Pacific rim
• Building vulnerability: areas where earthquakes are infrequent have limited precautions (e.g. Khillari, India 1993, stone houses with harvey insulating roofs)
• Economic impact: Japan has invested heavily in seismic research and technology since 1960s (e.g. Tokyo 2011, $235 billion damage)
• Social impacts: loss of life, injuries, homelessness, psychological trauma, social disruption, economic hardship, political instability