An earthquake sends P waves and S waves through the rock…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
An earthquake sends P waves and S waves through the rock. The P waves travel at and the S waves at . A seismograph records the S waves after the P waves.
- Which kind of wave is longitudinal, and which is transverse?
- How far is the seismograph from the earthquake?
- A station on the far side of the Earth records P waves but no S waves. Why?
Need a reminder? The key ideaShow
A wave carries energy and a pattern; each particle of the medium only moves about its own place. In a transverse wave the particles move across the direction of travel; in a longitudinal wave they move along it. The speed is .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The kinds. P waves are longitudinal. S waves are transverse.
Step 2. The travel times. Call the distance . The S waves take and the P waves take . So
Step 3. Solve. The bracket is . So .
Step 4. The far side. The Earth has a liquid outer core. A liquid does not resist a change of shape, so it cannot carry a transverse wave. The S waves stop there. The P waves are longitudinal and pass through.
Answer: about . Three stations, each finding its own distance, can locate the earthquake.
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