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Tectonic Hazards

The hazard profile and magnitude scales

  • 3 things to know
  • Component 3 Section A

Overview

Hazard profile, magnitude of a hazard and richter scale.

What you need to know

Answer each one before you reveal it.

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Key term

What is a hazard profile?

Key term

Define the magnitude of a hazard.

Numbers

Describe the Richter scale.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a hazard profile?

    Model answer

    A hazard profile is a summary of an event's physical characteristics, used to compare one hazard with another. Magnitude, speed of onset, duration, areal extent, frequency and predictability are the usual criteria.

  2. 2

    Define the magnitude of a hazard.

    Model answer

    Magnitude is the size or energy of a hazard event. Scales such as Richter, moment magnitude and the Volcanic Explosivity Index are used to record it.

  3. 3

    Describe the Richter scale.

    Model answer

    The Richter scale, devised in 1935, measures the amplitude of seismic waves recorded on a seismograph. The scale is logarithmic, so each whole number represents a tenfold rise in amplitude.

  4. 4

    How much more energy does a magnitude 7 earthquake release than a magnitude 6?

    Model answer

    Each whole step on the scale represents about 31.6 times more energy. A magnitude 7 event therefore releases roughly 32 times the energy of a magnitude 6.

  5. 5

    Why has moment magnitude replaced the Richter scale for large earthquakes?

    Model answer

    The Richter scale saturates above about magnitude 7 and understates the largest events. Moment magnitude uses fault area, slip and rock rigidity, so it stays accurate at any size.

  6. 6

    Describe the Modified Mercalli scale.

    Model answer

    The Modified Mercalli scale runs from I to XII and records the intensity of shaking. Ratings come from observed damage and from what people felt, not from an instrument.

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