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Tectonic Hazards

Ground shaking, liquefaction and landslides

  • 2 things to know
  • Component 3 Section A

Overview

How ground shaking damages buildings, peak ground acceleration and why soft sediment increases earthquake damage.

What you need to know

Answer each one before you reveal it.

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Key term

Explain how ground shaking damages buildings.

Key term

What is peak ground acceleration?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Explain how ground shaking damages buildings.

    Model answer

    Repeated horizontal acceleration puts shear stress on walls and joints designed only for vertical loads. Failure of a lower storey brings the floors above down on top of it.

  2. 2

    What is peak ground acceleration?

    Model answer

    Peak ground acceleration is the greatest acceleration of the ground during shaking, usually given as a fraction of gravity. Values above 0.3 g typically cause serious damage to ordinary buildings.

  3. 3

    What is resonance, and why does it matter in an earthquake?

    Model answer

    Resonance occurs when the shaking frequency matches a building's natural frequency, so the swaying grows. Buildings of one particular height can be destroyed while their neighbours survive.

  4. 4

    Explain why soft sediment increases earthquake damage.

    Model answer

    Loose sediment amplifies the amplitude of seismic waves compared with solid bedrock. Mexico City's lake-bed clays amplified the 1985 earthquake, whose epicentre lay around 350 km away.

  5. 5

    Define liquefaction.

    Model answer

    Liquefaction occurs when shaking causes saturated, loosely packed sand to behave as a fluid. Pore water pressure rises and the grains lose contact with one another.

  6. 6

    What are the consequences of liquefaction?

    Model answer

    Buildings tilt or sink because the ground loses its bearing strength. Buried pipes and tanks float upwards, and silt is ejected at the surface as sand volcanoes.

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