# A geologist uses seismic waves produced by an earthquake to investigate the structure of the Earth's interior. The seismic waves travel from the earthquake's source, pass through different layers of rock, and are detected at monitoring stations on the surface. Explain how the behaviour of seismic waves at boundaries between rock layers provides information about the Earth's interior structure.

> OCR A-Level Physics B: Advancing Physics (H557) — 5.3 Astrophysics and cosmology · Explain · 5 marks

> Seismic waves are produced by earthquakes and travel through the Earth. When they reach a boundary between two different rock layers, they can be partially reflected back and partially transmitted onward. Monitoring stations on the surface record the time at which the waves arrive.

## Mark scheme (5 marks)

1. Seismic waves are partially reflected at a boundary between two different rock layers / media
2. The remainder of the seismic waves are transmitted / continue through into the next layer
3. The speed of seismic waves is constant within a given medium, so the time taken for reflected waves to return to the surface can be used to calculate the depth of the boundary
4. When seismic waves pass into a denser / different rock layer their speed changes, causing refraction / change of direction
5. By analysing the pattern of reflected and refracted waves detected at multiple monitoring stations, scientists can map the depth, thickness and nature of different rock layers inside the Earth

## Key terms

- [seismic waves](https://www.gradenine.co.uk/glossary/seismic-waves)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-geologist-uses-seismic-waves-produced-74710652) · Published by Druglandscape Ltd.