Waves

A wave is a pattern. As the medium in which it travels is displaced, the wave is propagated. Wave motion can be described in terms of wave length, velocity and manner of propagation

For earth studies we mainly are concerned with two types of waves:
electromagnetic - including gamma, x-ray, light, infrared, radio
elastic - including sound and earthquake or seismic

Similarities between all waves:

wavelength (distance between identical points on the wave)
depends on the size of the disturbance creating the wave

The propagation of the waves involves changes in energy
for elastic waves - kinetic and potential energy
for electromagnetic waves - electrostatic and electromagnetic
energy

Elastic waves

modes of deformation:
compression - change in volume only
pure shear - change in shape only

We describe the ease of deformation
for compression - by the bulk modulus
for shear - by the shear modulus

Types of waves that travel through solids

transverse - particles transmit wave energy by moving vertically, while the wave travels horizontally (shear)

longitudinal - particles transmit wave energy by moving horizontally while the wave travels horizontally (compression)

Speed of waves determined by:
shear and bulk moduli
temperature
chemical composition
density of material
wavelength

Using these parameters we can develop equations for velocity

velocity depends on square root of ratio of elastic properties of the material (measured by shear and bulk moduli) divided by the density

compression waves travel faster than shear waves - thus
compression waves are called primary
shear waves are called secondary