Which seismic waves are alternatingly compressional and extensional, and cause rocks to change in volume?

Which seismic waves are alternatingly compressional and extensional, and cause rocks to change in volume?

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

Answer: (B)

P-waves are longitudinal seismic waves. The particle motion is parallel to the direction the wave travels, so the material is repeatedly compressed and then stretched as the wave passes. This alternating compression and rarefaction changes the rock’s volume, which is the hallmark of these waves. S-waves are transverse and move the material side-to-side or up-and-down perpendicular to the travel direction, so they deform rocks but don’t produce the same volume changes. Love waves are a type of surface wave with horizontal shear motion, which also involves deformation without the kind of volumetric compression and expansion seen in P-waves. Surface waves in general involve motion at the surface rather than the bulk’s compressional/rare faction behavior.

P-waves are longitudinal seismic waves. The particle motion is parallel to the direction the wave travels, so the material is repeatedly compressed and then stretched as the wave passes. This alternating compression and rarefaction changes the rock’s volume, which is the hallmark of these waves.

S-waves are transverse and move the material side-to-side or up-and-down perpendicular to the travel direction, so they deform rocks but don’t produce the same volume changes. Love waves are a type of surface wave with horizontal shear motion, which also involves deformation without the kind of volumetric compression and expansion seen in P-waves. Surface waves in general involve motion at the surface rather than the bulk’s compressional/rare faction behavior.