Consider the following statements: I. In seismograph, P waves are recorded before S waves. II. In P waves, the particle waves vibrate back and forth in the direction of wave propagation, while in S waves the particle waves vibrate perpendicular to the direction of wave propagation. Which of the statements given above is/are correct?

Statement I is correct: P (primary) waves are the fastest seismic waves (≈ 6 km/s in crust) and are the first to be recorded by a seismograph; S (secondary) waves are slower (≈ 3.5 km/s) and arrive later. Statement II is also correct: P waves are longitudinal/compressional waves in which particles oscillate parallel to the direction of wave propagation, while S waves are transverse waves in which particles oscillate perpendicular to the direction of propagation. Hence both statements are correct.