Seismic Hazards

• The Nepal earthquake occured in 2015 with a magnitude of 7.8, the epicentre was 50 miles from Kathmandu. Nepal's HDI is 143rd
• Nepal is land locked in East Asia, on the Himalayas which lies on 2/3 major reverse faults
• The earthquakes in Nepal are caused by the Indo-Australian plate slamming into the Eurasian plate, creating an accretionary wedge which creates the Himalayas. It is on 2/3 major reverse faults and most places are in the upwards parts
• Impacts of the Nepal Earthquake

  • 9000 died
  • 23,000 injured
  • 700,000 pushed to the brink of poverty
  • 40,000 chickens die when 65% of the country rely on agriculture
  • 4.3km avalanche in Langtang Valley killed 300
• Responses to the Nepal Earthquake

  • US gave $10 million aid
  • UK gave $7.8 million aid
  • 'tent cities' set up (can be dangerous)
  • Monsoon prevented satelittes
  • ADB gave $3 million short term and $200 million long term
  • Long after, 13,000 people still live in temporary housing
• As tectonic plates move over, under and against each other, the stresses generated through frictional drag build to breaking point, resulting in earthquakes
• Earth shaking (seismicity) can be caused by human activities such as mining, fracking or reservoir construction. But it is most strongly associated with plate tectonics
• Friction along plate margins builds stresses in the lithosphere. When the strength of the rocks under stress is suddenly overcome, they fracture along cracks called faults, sending a series of seismic shockwaves to the surface.
• The breaking point of friction is called the focus (hypocentre)
• The epicentre is the point on the surface directly above the focus
• Primary or pressure (P) waves are the fastest and reach the surface first. P waves are like sound waves – high-frequency and pushing like balls in a line. They travel through both the mantle and core to the opposite side of the Earth.
• Secondary or shear (S) waves are half as fast and reach the surface next. Like P waves they are high-frequency but shake like a skipping rope. They can travel through the mantle, but not the core, so cannot be measured at a point opposite the focus or epicentre.
• Surface Love (L) waves are the slowest waves and cause most of the damage, travelling side to side
• Rayleigh (R) waves radiate from the epicentre in complicated lowfrequency rolling motions.
• Tsunamis are caused by seismic activity such as ocean floor earthquakes or submarine volcanic eruptions. Can aslo be caused by massive landslides
• Tsunamis have a very long wavelength ranging from 100 to 1000km
• Tsunamis have a low wave height (less than 1m), but upon reaching the shore they can rise to over 25m
• Tsunamis travel very quickly, speeds between 640km and 960km per hour
• Hawaii has a Pacific Tsunami Warning System which gives many hours notice of waves following important, major and serious seismic events
• Furthermore, both the intensity and depth of earthquakes varies according to the type of plate margin – whether constructive, destructive or conservative
• Magnitude of earthquakes is measured on the Richter Scale, a logarithmic scale which using maths to interpret the distance moved by the pen on a seismograph
• The Richter Scale has also been developed to calculate the total energy released
• The Mercalli Scale uses observations of damage to deduce the impacts of the earthquake from I to XII
• The frequency and regularity of earthquakes shows little predictability
• Predicting earthquakes

  • Microquakes before main tremour
  • Ground bulging
  • Decreased radon gas
  • Raised groundwater levels
  • Electrical and magnetic changes in rock
  • Increased argon
• Earthquake damage mitigation strategies

  • Rubber shock absorbers and reinforced latticework in foundations
  • Interlocking steel frames
  • Reinforced lift shafts with tension cables
  • Marble and glass flexibly anchored
  • Rolling weights on roof to counteract shock waves
• Soil liquefaction = soil becomes loose and flows downhill due to water pressure
• Indian Ocean Tsunami, December 2004

  • Followed a magnitude 9.0 earthquake
  • 15m of 1600km of sea bed in the ocean led to massive tsunamis, killing approximately 300,000 people across two continents
  • Waves of up to 20m began to crash into Sumatra, only 15 minutes after the initial earthquake
• Impacts of Indian Ocean tsunami

  • 300,000 deaths
  • Vegetation destroyed up to 800m inland
  • Infrastructure destroyed, Nicobar island cut off
  • 500,000 forced into refugee camps
  • Thailand suffered a £226 million loss of fishing
• Responses to the Indian Ocean tsunami

  • Over 160 aid organisations involved
  • Aid was slowed due to political boundaries
  • The dalits in India (underclass) were ignored by the government
  • Tourist resorts rebuilt as coastal communities ignored
  • Hazard mapping
  • Education
• Landslides (earthquakes) = Slope failure as a result of the grounf shaking
• Earthquakes cannot really be prevented, however, studies are being carried out lubricating active faults with water and oil to stop them becoming stuck
• Adapting to Earthquakes

  • Land use planning = identifying areas at risk and limiting land use, putting key buildings in low risk areas, including open spaces to allow safety away from infrastructure
  • Change in behaviour
  • Emergency services trained in heavy lifting gear to deal with casualties
• Preparedness for Earthquakes

  • Heavy items stores at a low level
  • Family communication plans and emergency meeting places
  • Household emergency supply kits
  • Structurally sound infrastructure
  • Earthquake insurance policy