Starter

What will be the initial, or primary effect (impact), of an earthquake? The severity of which factors will depend upon it?

Effect (impact) of earthquake

Primary:

• ground shaking
  the severity of which will depend upon
  • the magnitude of the earthquake,
  • its depth,
  • the distance from the epicentre and
  • the local geological conditions. [?]
• ground rupture
  - visible breaking and displacement of the earth’s surface, probably along the line of the fault.
  - poses a major risk for large engineered structures such as dams, bridges and nuclear power stations.

Secondary:

• soil liquefaction:
  - when violently shaken, soils with a high water content lose their mechanical strength and start to behave like a fluid.
• landslides/avalanches:
  - slope failure as a result of ground shaking
• tsunamis:
  - slope failure as a result of ground shaking
• fires:
  - resulting from broken gas pipes and collapsed electricity transmission systems
• effects on people and the built environment:
  • collapsing buildings;
  • destruction of road systems and other forms of communication;
  • destruction of service provision such as water, electricity and gas;
  • flooding;
  • disease;
  • food shortages;
  • disruption to the local economy, either subsistence or commercial. {[?]

Tsunamis

What do you already know about Tsunami?

Tsunamis

- giant sea waves (tsunami means ‘harbour wave’ in Japanese) generated by:

• shallow-focus underwater earthquakes (the most common cause)
• volcanic eruptions
• underwater debris slides and
• large landslides into the sea.

Tsunamis

Read the information about tsunamis on pages 203-204 in the Hodder textbook 4th edition, then answer the following questions:

• What are the key features of tsunamis?
  • a very long wavelength (sometimes over 100 km) and
  • a low wave height (under one metre) in the open ocean
  • travel quickly at speeds of over 700 km per hour
  • when reaching shallow water bordering land, increase rapidly in height.
• When a tsunami reaches land, its effects will depend upon what?
  • the height of the waves and the distance they have travelled
  • the length of the event (at source)
  • the extent to which warnings could be given
  • coastal physical geography, both offshore and on the coastal area
  • coastal land use and population density
• Why are 90% of tsunamis generated in the Pacific Basin?
  • associated with the tectonic activity taking place around its edges.
  • most are generated at convergent (destructive) plate boundaries where subduction is taking place, particularly on the western side of the Pacific and the bordering eastern side of the Indian Ocean (25 per cent of all events).

Tsunamis

Using information from p.204 the Hodder textbook) and/or the internet, complete the 5Ws table below for either the December 2004 Boxing Day tsunami or the March 2011 Tohoku tsunami.



Challenge: Describe the characteristics of tsunamis and explain their formation [9 marks].