Earthquakes

• Earthquakes are sudden vibrations in the earth's crust that are as a result of tectonic movement
• Earthquakes are associated with crustal plate movements
• Earthquakes are caused by

  1. volcanic activity for example Nevada del Ruiz
  2. Isostatic djustments for example in the Andes or Himalayas
  3. Folding and faulting for example in the East African Rift Valley
  4. Shearing friction e.g Pacific plate and North American Plate
  5. Subduction friction e.g Nazca plate and South American Plate
• Earthquakes usually occur in areas such as

  1. Pacific Ring of fire where there is a destructive plate boundary
  2. Central Asia where there is a collision zone like in Bangladesh and Nepal
  3. In South America - West Coast there is a destructive and South Coast a conservative
  4. In the Atlantic where there is sea floor spreading
  5. Hotspots in major oceans
• Distribution of earthquakes

  1. Subduction zone by the Nazca and South American Plate
  2. In the Atlantic Ocean due to sea floor spreading
  3. Conservative where plates slide past each other in the San Andreas fault or the East African Rift Valley
  4. Aleutian trench where the Pacific sinks under the Eurasion
  5. Java Trench, where Indo Australian sinks under Eurasion
• Earthquakes occur because of the movement of tectonic plates moving towards each other or sliding past each other. As they converge or slide past each other, they have rough edges so they stick in one position and then they lock or jam. As they try to move away from each other great stress and pressure build up. Heat is generated due to friction. Eventually, that great pressure is then released and sends out vibrations and shock waves called seismic waves out into the earth.
• The hazards ssociated with  earthquakes are

  1. Ground Shaking
  2. Landslides and Avalanches
  3. Tsunamis
  4. Soil liquefaction
• Effects of earthquakes

  1. Loss of life
  2. Destruction of buildings, roads and infrastructure
  3. Water borne diseases for example cholera
  4. Stray gas from raptured gas pipes and fires from open cables and wires
• Measures to reduce the effects of earthquakes

  1. Monitoring and Prediction

  2. Community preparedness

  3. Controlled underground explosions

  4. Aid from NGOs

  5. Reinforced buildings
• Monitoring and Prediction


  Use of tilt meters, seismographs and looking out for any signs of earthquakes like cracks in rocks, strange animal behaviour and rising water levels
• Monitoring and Prediction worked for the Haicheng earthquake but not the Tangshen one
• Community preparedness


  Availability of all government emergency services and the education of citizens
• Reinforced buildings


  Putting shock absorbers into the foundations, reinforcing the foundations with steel, using lighter building materials, all so that the impact is absorbed
• Methods to predict and monitor earthquakes include

  1. Satellite Survey
  2. Radon gas sensors
  3. Tilt meters
  4. Strain meters
  5. Seismometeres
• You can evaluate the effectiveness of the prediction methods by looking at cost and accuracy, as well as look at examples of successes and failures
• Difficulties associated with prediction of earthquakes :

  1. Economic development - affordability
  2. Some come suddenly with no tell tale signs
  3. Some bring about multiple after shocks which may not be easily predicted