2.4.1 Earthquake Hazards

Question 1

Types of Earthquake Hazards

Answer 1

1. Ground Shaking
2. Soil liquefaction
3. Landslides
4. Tsunamis

Question 2

(1) How does ground shaking affect natural systems

Answer 2

• destroys ecosystems
• ruptures oil and chemical factories, polluting land and water
• fractures and uproot trees, causing widespread tree injury and death and damaging wildlife habitats

Question 3

(1) How does ground shaking affect human systems?

Answer 3

• weaken buildings, bridges, roads and railways
• makes it difficult to rescue people or supply emergency aid
• snaps water and gas pipes ➡️ results in water shortages and disruptions to gas supply
• Electricity and communication cables break ➡️ affect important communication services such as tsunami warnings and television broadcasts.
• people may get trapped under collapsed buildings and infrastructures, resulting in deaths and injuries

Question 4

(1) Example of ground shaking

Answer 4

*2010 Haiti earthquake (Mw 7.0)**:
- Surrounding areas around factories were polluted. - Debris polluted rivers.
- More than 250,000 houses collapsed due to violent vibrations.
- About 220,000 people were killed.
- Water pipes ruptured, causing water shortages.

Question 5

(2) Liquefaction

Answer 5

• occurs when the violent ground shaking causes saturated loose soil to lose its structure and transforms into a think liquid

Question 6

(2) Impacts of soil liquefaction on ecosystems

Answer 6

• Destroys ecosystems
• Trees on liquefied soil sink in and tip over, damaging wildlife habitats, causing forest and biodiversity loss.
• Liquefied soil may enter rivers and smother aquatic plants, causing them to die.
• Sewage pipes may be broken and untreated waste materials may pollute rivers, killing aquatic species.

Question 7

(2) How do soil liquefaction affect human systems

Answer 7

• Buildings and other infrastructure can sink in and tip over, and damage makes it difficult to rescue people or supply emergency aid.
• Electricity and communication cables, and water and gas pipes can sink in and snap, disrupting supply of these services.
• Roads and railways above liquefied soil can sink in and get damaged, making it difficult to rescue people or supply emergency aid.
• People can get trapped under collapsed buildings and infrastructure, resulting in injuries and loss of lives.

Question 8

(2) Example of soil liquefaction

Answer 8

**2010-2011 Christchurch, New Zealand earthquakes (Mw 6.3) **:
- Triggered severe liquefaction, as the city lies on a former swamp area where soils are loose and saturated.
- More than 60,000 residential buildings and infrastructure covering about one-third of the city area were damaged.
- Liquefied soil entered rivers, and untreated sewage from broken pipes polluted rivers.
- This resulted in the reduction of some species such as the caddisflies.

Question 9

(3) Landslides

Answer 9

Landslides occur as the violent vibrations:
1. Form cracks on steep slopes, loosening the rocks and soil.
2. Trigger the loose rocks and soil to move downslope.

Question 10

(3) Impacts of landslides on ecosystems

Answer 10

• Fast-moving debris can bury huge areas of forest and wetlands.
• Rivers can be polluted with debris, killing aquatic life.
• Rivers can be blocked, causing floods that can damage nearby ecosystems and properties.

Question 11

(3) Impacts of landslides on human systems

Answer 11

• Debris can bury villages and farms, destroying properties and infrastructure.
• Debris can snap electricity and communication cables, and water and gas pipes, disrupting supply of these services.
• Roads and railways can be blocked by debris, making it difficult to rescue people or supply emergency aid.
• Debris can bury people or hit them, causing injuries and loss of lives.
• Debris can block rivers, resulting in floods, which can drown people

Question 12

(3) Examples of landslides

Answer 12

**2008 Great Sichuan, China Earthquake (Mw 7.9) **:
- Triggered more than 15,000 landslides.
- Destroyed many buildings and infrastructure.
- Caused nearly 20,000 deaths

Question 13

(4) Tsunamis

Answer 13

• Tsunamis are a series of ocean waves which can be caused by undersea earthquakes.
• can travel over thousands of kilometres and devastate huge areas of coastline.
• Tsunamis occur when:
  1. An undersea earthquake causes the seabed to be displaced.
  2. A large volume of water is lifted, forming waves of great wavelength and low height of less than 1 metre.
  3. The waves travel towards land at high speeds around 800km/h.
  4. On approaching the coast, greater friction with the shallower seabed slows the waves down.
  5. The waves get closer together and increase in height. Waves can reach up to a height of 15m or more, travel at a speed of 30 - 50km/h and devastate shorelines the waves hit.
  6. Before a tsunami occurs, the sea may recede from the shore because the sea water fills in the void caused by displacement of the seabed.

Question 14

(4) Impacts of tsunamis on ecosystems

Answer 14

• The seawater can flood huge areas of coastal wetlands and forests, damaging habitats.
• Large amounts of debris carried in by the waves can pollute these areas, damaging ecosystems and killing wildlife.

Question 15

(4) Impacts of tsunamis on human systems

Answer 15

Fast moving waters and the large amounts of debris carried in by the waves can:
- sweep away buildings and infrastructure, destroying them.
- snap electricity and communication cables, disrupting supply of these services.
- sweep away roads and railways, making it difficult to rescue people or supply emergency aid.
- drown people
- debris can hit and kill people

Question 16

(4) Example of tsunamis

Answer 16

2004 Indian Ocean Tsunami:
- Triggered by a 9.1 Mw undersea earthquake near Sumatra, Indonesia.
- Tsunami waves slammed into the coasts of 11
Indian Ocean countries, from Indonesia to Somalia in Africa.
- More than 230,000 people were killed and
entire coastlines and habitats were destroyed.