Seismic Hazard (primary + secondary etc)

• What is the primary hazard caused by seismic activity?

  Earthquakes
• How do earthquakes occur?

  They occur due to the buildup of pressure as plates move along a fault.
• What are the secondary hazards associated with earthquakes?

  Secondary hazards include landslides, tsunamis, flooding, and fires.
• What causes landslides during an earthquake?

  The shaking of the ground can dislodge rock, soil, or snow.
• What is soil liquefaction?

  Soil liquefaction occurs when violently shaken soils lose their mechanical strength and behave like a fluid.
• What can ground rapture cause during an earthquake?

  It can cause damage or ripping apart of structures.
• How can flooding occur as a result of an earthquake?

  Flooding can occur if an earthquake ruptures dams or levees along a river.
• What are the potential consequences of fires after an earthquake?

  Fires can result from broken gas pipes and collapsed electricity systems.
• What was the impact of the San Francisco earthquake in 1906?


  The city burned for 3 days, leaving most of it destroyed and 250,000 people homeless.
• What are the seismic hazards and their impacts?

  • Earthquakes: Primary hazard causing ground shaking.
  • Landslides: Dislodging of rock, soil, or snow.
  • Tsunamis: Giant sea waves from underwater earthquakes.
  • Soil liquefaction: Soils behave like a fluid when shaken.
  • Ground rapture: Damage to structures from ground shaking.
  • Flooding: Caused by ruptured dams or levees.
  • Fires: Resulting from broken gas pipes and electricity systems.
• • Ground Rapture:
  • When the ground shakes across a fault, causing damage or ripping apart a structure, e.g., a building.
  • can lead to flooding as an earthquake can rapture dams or levees along a river. Causing the water from the river or reservoirs to then flood an area, damaging buildings, sweeping people away and drowning them.
• • Tsunamis:
  • When an oceanic crust is jolted during an earthquake, all of the water above this plate is displaced.
  • The water travels fast but with a low amplitude (height). As it gets closer to the coast, the sea level decreases, so there is friction between the sea bed and the waves.
  • This causes the waves to slow down and gain height, creating a wall of water that is on average 10 feet high, but can reach 100 feet.
• Tsunamis usually occur close to plate boundaries and are most common in the area surrounding the Pacific Ocean - 'Ring of Fire'
• Give examples of tsunamis:

  1. 2004 Indian Ocean tsunami
  2. 2011 Tohoku earthquake in Japan triggered tsunami waves of up to 40 meters, which travelled inland for several kilometres in some areas
• Earthquakes alone do not cause direct danger to people. A person cannot be shaken to death. However, the secondary effects of earthquakes can be fatal due to urbanisation.


  Primary hazard = The earthquake

  Secondary hazards = tsunamis, ground rapture, fires, liquefication, and landslides.
• • The risk of landslides is greater where soils are looser, slopes are steeper and where the shaking lasts longer or is particularly intense
• Give examples of when an earthquake has caused a landslide:

  1. the 2008 Sichuan earthquake in China, approximately 60,000 landslides were a major factor contributing to the devastation.
  2. The 2015 Gorka earthquake in Nepal also triggered more than 3000 avalanches and landslides
• What are the primary effects of seismic hazards?


  1. Environmental = Earthquakes can cause fault lines, which destory the environment
  2. Economic = Destruction of businesses
  3. Social = Buildings collapsing due to ground raputre can kill, injure and trap people
  4. Political = Government buildings destroyed
• What are the secondary effects of seismic hazards?


  1. Environmental = Radioactive materials and other dangerous substances leaked from power plants. Saltwater from tsunamis flooding freshwater ecosystems. Soil salinisation
  2. Economic = General economic decline. High cost of rebuilding and insurance payout. Sources of income at a loss for some. eg toursim
  3. Social = Water supplies are contaminated, and pipes bursting spread disease rapidly and cause floods.
  4. Political = Food and water shortages can cause political unrest. They can also cause chaos and lawlessness, e.g., looting.