Consider the following statements:1.In a seismograph, P waves are recorded earlier than S waves.2.In P waves, the individual particles vibrate to and fro in the direction of wave propagation whereas in S waves, the particles vibrate up and down at right angles to the direction of wave propagation.Which of the statements given above is/are correct?

1. A

   1 only

   1 only. Both the arrival order and the particle motion are standard.

2. B

   2 only

   2 only. P waves are recorded first.

3. C

   Both 1 and 2

   Both. P before S; P is longitudinal, S is transverse.

4. D

   Neither 1 nor 2

   Neither. Both statements are textbook seismology.

Summary. Official key is (c) both. P (primary) waves are faster, so a seismograph records them before S (secondary). P motion is compressional (to-and-fro along the path); S motion is shear, at right angles to the path.