● Different types of earthquake waves travel in different manners. ● As they move or propagate, they cause vibration in the body of the rocks through which they pass. ● Primary waves (P-waves) vibrate parallel to the direction of the wave. ◌ This exerts pressure on the material in the direction of the propagation. As a result, it creates density differences in the material leading to stretching and squeezing of the material. Hence statement 1 is correct. ◌ Density difference is created by P-waves. ● The direction of vibrations of secondary waves (S-waves) is perpendicular to the wave direction in the vertical plane, hence they create troughs andcrests in the material. Hence statement 2 is correct.