Seismic Waves and the Structure of the Earth
Master Seismic Waves and the Structure of the Earth for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) physics topic: p-waves are longitudinal and S-waves are transverse, and the way they travel through the Earth reveals its layered structure.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
This is a Higher tier only topic, so there's no Foundation paper — only the Higher worksheet and mark scheme below.
Topic overview
Seismic waves are produced by earthquakes, and studying them has revealed the internal structure of the Earth. This is a Triple-only and Higher-only topic.
P-waves are longitudinal and travel through both solids and liquids. S-waves are transverse and travel through solids only. This difference is the key evidence.
Because S-waves cannot pass through the outer core, there is an S-wave shadow zone on the far side of the Earth from an earthquake. This provided evidence that the outer core is liquid. P-waves are also refracted as they pass through the core, changing direction because their speed changes, which gave evidence about the size of the core.
Revision notes
The two wave types
P-waves are longitudinal and travel through both solids and liquids.
S-waves are transverse and travel through solids only. This difference in behaviour is what allowed the Earth's internal structure to be deduced.
The shadow zone
S-waves cannot pass through the outer core, so they are not detected on the far side of the Earth.
This S-wave shadow zone provided the evidence that the outer core is liquid, since transverse waves cannot travel through a liquid.
Refraction of P-waves
P-waves change speed as they pass into and through the core, so they are refracted and change direction.
Studying where P-waves arrive allowed the size and position of the core to be determined. This is a good example of conclusions drawn from indirect evidence.
Key points
- P-waves are longitudinal.
- P-waves travel through solids and liquids.
- S-waves are transverse.
- S-waves travel through solids only.
- The S-wave shadow zone shows the outer core is liquid.
- P-waves refract as their speed changes.
Worked examples
Example 1
State one difference between P-waves and S-waves. [2 marks]
Model answer
P-waves are longitudinal and can travel through both solids and liquids (1 mark). S-waves are transverse and can only travel through solids (1 mark).
Example 2
Explain how the S-wave shadow zone provides evidence that the outer core is liquid. [3 marks]
Model answer
S-waves are transverse and cannot travel through liquids (1 mark). They are not detected on the far side of the Earth from an earthquake, creating a shadow zone (1 mark). This shows they have been unable to pass through the outer core, so the outer core must be liquid (1 mark).
Example 3
Explain why P-waves change direction as they travel through the Earth. [2 marks]
Model answer
The speed of the P-waves changes as they pass into materials of different density (1 mark), and a change in wave speed causes refraction, so the waves change direction (1 mark).
Common mistakes
Saying S-waves travel through liquids.
They are transverse and cannot travel through liquids, which is the whole basis of the evidence.
Confusing P and S wave types.
P is longitudinal (primary, faster); S is transverse (secondary, slower).
Not linking the shadow zone to the conclusion.
The absence of S-waves is the evidence for a liquid outer core.
Saying refraction is caused by density alone.
It is caused by the change in wave speed, which density affects.
Exam tips
- Learn the two wave types with their properties as a pair.
- Explain the shadow zone as evidence, step by step.
- Link refraction to changing wave speed.
- Remember this is Triple-only AND Higher-only.
Key terms
- P-wave
- A longitudinal seismic wave travelling through solids and liquids.
- S-wave
- A transverse seismic wave travelling through solids only.
- Shadow zone
- A region where waves are not detected.
- Outer core
- The liquid layer shown by the S-wave shadow zone.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.