Magnitude

Definition

A measure of an earthquake’s size, related to the energy it releases.

Used by AQA, Edexcel and OCR

Specification 3.1.1.1 · Paper 1, Paper 2, Paper 3

The size or strength of a natural event.
Magnitude means the size or strength of an event. A stronger earthquake or more intense storm generally has greater potential to cause damage. However, magnitude alone does not determine the outcome: a powerful event affecting few people may cause less harm than a smaller event in a densely populated, vulnerable settlement.
Revise: Natural Hazards
The size or amount of something, such as the size of a geographical event.
Revise: Quantitative Analysis

1
For magnitude comparisons, a one-unit increase means ten times the recorded wave amplitude, not ten times the energy or damage.
2
When comparing shallow and deep earthquakes, qualify your explanation with ‘for earthquakes of similar magnitude’.
3
Magnitude describes earthquake size; it is not the same as intensity, which describes shaking and its effects at a particular location.

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Paper 1

For earthquakes of similar magnitude, shallow earthquakes generally produce stronger shaking near the epicentre. Their seismic waves have a shorter distance to travel before reaching the surface. Waves from a deeper earthquake travel further, spreading their energy over a larger area before reaching the surface.
Revise: Causes and Measurement of Earthquake Hazards

Specification 1.2b, 9.3 · Paper 1, Paper 2, Paper 3

A measure of the size of an earthquake, related to the energy released.
In April 2015, a magnitude 7.8 earthquake struck Nepal, a landlocked country between India and China. Its epicentre was approximately 80 km north-west of Kathmandu, in the Gorkha district. Around 9,000 people died and more than 20,000 were injured.
Revise: Tectonic Hazards
The size of something, such as the size of an earthquake.
Revise: Basic Number Skills, Scale, and Percentages