Science Olympiad Dynamic Planet Practice Test

Which seismic wave is slower, P wave or S wave?

1. P wave

2. S wave

3. Both travel at the same speed

4. Neither, they're equally fast

The correct answer is: S wave

Seismic waves are classified into two main types: primary (P) waves and secondary (S) waves. P waves are compressional waves that travel through solids, liquids, and gases. They are the fastest seismic waves and are the first to be detected by seismic stations after an earthquake occurs. On the other hand, S waves are shear waves that only move through solids. They cannot move through liquids or gases, which is a crucial characteristic. S waves travel slower than P waves, making them the second to be detected following an earthquake. The speed difference is significant, with P waves generally traveling at about 5 to 8 kilometers per second, while S waves typically travel at about 3 to 4.5 kilometers per second in the Earth's crust. This inherent speed difference is due to the nature of the wave propagation where P waves compress and expand the medium, allowing for faster movement, whereas S waves require a shear mechanism that is inherently slower. Thus, S waves are indeed slower than P waves, confirming that the correct answer is that S waves are the slower of the two seismic wave types.