As an important application of the theory of elasticity in soil mechanics, the main principles of elastodynamics are introduced. On the basis of waves in 1D-continua the notions of transmission, reflexion and dynamic stiffness are explained, and the body waves are presented as compression and shear waves. Rayleigh waves are presented as an example of surface waves.

The seismic signals from major events continue to propagate through the Earth for hours. Theapplication of correlations between seismic stations to these long codas extracts steeply travelling body waves as the main contributors to the correlation wavefield.The properties of the coda correlation depend on the differences between the seismic phases that are being correlated. As a result, the correlation wavefield of the coda emphasises seismic phases that are difficult to detect in direct excitation by a source and so can provide new information on internal structure, e.g., an improved estimate of the shear wavespeed in the inner core.

The book covers propagation of seismic waves on all scales from the global to the local. We start by providing a discussion of the way that the higher frequency body wavesand surface wave components emerge from the normal mode spectra of the Earth for radially stratified structure. Thistreatment provides a formulation that links global and local concepts, which is exploited in later chapters. We introduce the description of seismic wave propagation in terms of reflection and transmission through zones of Earth structure and show how this enables understanding of the physical processes that lead to observed seismic signals.

The structure of the earth varies in 3-dimensions superimposed on the dominant trend of increase of seismic wavespeed with depth.We consider integral representations of the wavefield for media with horizontal variations, and from these develop the concepts of reflection and transmission operators that allow insight gained in the discussion of stratified media to be transferred to a more general 3-D environment.This operator approach also provides a convenient link between larger scale seismology and seismic reflection studies., and also helps in assessing approximations for propagation of both body waves and surface waves