1.2.3

Comparing Hazards

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Measuring the Intensity of Tectonic Hazards

The magnitude and intensity of tectonic hazards are measured using a variety of different scales.

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Earthquake magnitude

  • The amount of energy released is measured by the Moment Magnitude Scale (MMS), which is a version of the old Richter scale.
    • The MMS goes from 1 to 10, with a higher number meaning greater magnitude.
    • The scale is also logarithmic. This means that an increase of 1 unit of magnitude increases the amount of shaking by 10, but the amount of energy released by 30.
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Earthquake damage

  • The damaging effects of earthquakes are measured by the Mercalli scale.
    • The Mercalli scale measures the intensity of shaking on a scale of 1 to 12 (usually given as Roman numerals).
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Volcano magnitude

  • Volcano magnitude is measured by the Volcanic Explosivity Index (VEI).
    • The VEI is based on the volume, duration and column height of eruptions.
    • The explosivity is related to the type of magma and the type of plate boundary that the volcano is located on.
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VEI examples

  • Effusive eruptions of basaltic lavas with low VEI (0 to 3) normally happen on constructive boundaries.
  • Explosive eruptions with high VEI (4 to 7) happen on destructive boundaries.

Hazard Profiles

Hazard profiles can be used to compare the characteristics of tectonic hazards.

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What do hazard profiles show?

  • Hazard profiles summarise the physical processes shared by all hazards so that decision-makers can determine which areas are most at risk.
  • Hazard profiles show how different types of hazards vary in:
    • Magnitude.
    • Speed of onset.
    • Areal extent (the area that will be affected).
    • Duration.
    • Frequency.
    • Spatial predictability.
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High-risk events

  • Events which present the highest risk have:
    • High magnitudes.
    • Low frequencies.
    • Rapid speeds of onset.
    • Low spatial predictability.
    • Large areal extents.
  • These high-risk events happen mostly at subduction and collision zones.

2005 Kashmir Earthquake

Kashmir, in Northern India, was hit by a severe earthquake in 2005, killing at least 79,000 people.

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Hazard profile

  • A high magnitude (MMS 7.6) earthquake hit Kashmir in 2005, with a ground-shaking intensity of VII (severe).
  • The speed of onset was very rapid, so there was a limited chance of evacuating to a safe area.
  • Damage was centred on Muzaffarabad but spread over a large area of more than 1000 km2
  • Ground shaking lasted 30–45 seconds (a short duration), but landslides triggered by the earthquake continued for some time, as did aftershocks up to magnitude MMS 6.4.
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Hazard profile cont.

  • Earthquakes don't hit Kashmir often. The previous major earthquake in Kashmir was in 1905, so there was no ‘collective memory’ of the risks and impacts of earthquakes in the region.
  • Spatial predictability was low. Kashmir is in a ‘seismic gap’, i.e. an area of known risk that had not experienced an earthquake for some time.

Jump to other topics

1Tectonic Processes & Hazards

2Option 2A: Glaciated Landscapes & Change

3Option 2B: Coastal Landscapes & Change

4Globalisation

5Option 4A: Regenerating Places

6Option 4B: Diverse Places

7The Water Cycle & Water Insecurity (A2 only)

8The Carbon Cycle & Energy Security (A2 only)

9Superpowers (A2 only)

10Option 8A: Health & Human Rights (A2 only)

11Option 8B: Migration & Identity (A2 only)

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