Which seismic waves move particle motion perpendicular to the direction of travel?

Which seismic waves move particle motion perpendicular to the direction of travel?

• A. P-waves
• B. Surface waves
• C. S-waves
• D. Love waves

Answer: (C)

Motion perpendicular to the direction of travel is the hallmark of transverse (shear) waves. S-waves are shear waves, so the particles in the material move side to side (or up and down) perpendicular to the wave’s propagation direction as the wave passes. P-waves, by contrast, are compressional waves where particles move parallel to travel, compressing and expanding the material. Surface waves have more complex motion patterns (Love waves involve horizontal shear along the surface, Rayleigh waves involve elliptical motion in a vertical plane), but the direct, classic example of perpendicular particle motion is the S-wave, making it the best answer.

Motion perpendicular to the direction of travel is the hallmark of transverse (shear) waves. S-waves are shear waves, so the particles in the material move side to side (or up and down) perpendicular to the wave’s propagation direction as the wave passes. P-waves, by contrast, are compressional waves where particles move parallel to travel, compressing and expanding the material. Surface waves have more complex motion patterns (Love waves involve horizontal shear along the surface, Rayleigh waves involve elliptical motion in a vertical plane), but the direct, classic example of perpendicular particle motion is the S-wave, making it the best answer.