Step-by-step explanation:
Both P and S-waves travels as body waves within the earth.
They are seismic waves. P-waves are longitudinal waves and as such can travel through any material medium. S-waves are transverse waves can only travel through solids.
- If the earth is uniformly solid, at the seismograph station, both waves would be picked.
- Based on travel time, p-waves will reach the station first before s-waves.