Seismic Waves

Body Waves

• penetrate the body of the Earth
• travel faster in more elastic rocks
• body wave velocities increase with depth in the interior of the Earth
• subject to refraction and reflection
• increased rock temperature = decreased velocity
• increased confining pressure = increased velocity

Figure 1. A) P-wave motion. B) S-wave motion.

P-Waves

• primary waves, compressional waves
• fastest seismic waves
• wave motion: energy moves as a succession of compressions and expansions in the direction of wave travel - an accordion-like push-pull movement
• each square in the figure changes from square to rectangle to square again as the waves move through the rock
• travel through solids, liquids, & gases

S-Waves

• secondary waves, shear waves
• slower than P-waves
• wave motion: rock segments vibrate perpendicularly (at right angles, up-and-down or side-to-side) to the direction of wave travel - this more complex motion causes S-waves to travel more slowly
• travel through solids only

Surface Waves

• large-motion waves that travel through the outer crust of the Earth
• wave pattern resembles ripples caused when a pebble is dropped in a pond
• slowest seismic waves
• cause of destruction during an earthquake since they are channeled through the thin crust and their energy is less rapidly dissipated than body waves

Figure 2. a) Rayleigh wave motion. b) Love wave motion. 

c) Surface expression of wave motion of Rayleigh & Love waves

Rayleigh Waves

• wave motion is similar to waves in an ocean (see figure)

Love Waves

• wave motion is a shear which moves the surface from side to side