The inspiration for this book came from the remarkable series of articles written by Beno Gutenberg in the 1930's for the multi-volume Handbuch der Geophysik on the theory and observations of waves from earthquakes that captured most of what was known at the time.

With the subsequent growth of studies in Seismology, it would be rash for any individual to attempt to cover the füll field. Nevertheless, this book has arisen from the need to provide a broad survey of the nature of seismic wave observations and the relation of the seismic wavefield to the structure of the Earth. In the last decade the volume of high quality digital observations has grown enormously with the development of high quality global networks as well as the widespread use of broad-band recording using portable instrumentation. Yet, at the same time, the switch from analogue to digital presentation means that more effort is required to obtain an overview of the seismic wavefield.

The focus of this book is on observations of earthquakes and man-made sources, from the near-source region out to thousands of kilometres from the source, for both body waves and surface waves. The emphasis is on frequencies above 10 mHz so that the development can be regarded as complementary to the free oscillation orientation of Theoretical Global Seismology by Dahlen and Tromp (1998).

The aim is to relate observations to the relevant physical processes. The link to theory is made at a number of levels, starting with a broad survey and then progressing towards more detail. The first part provides a survey of the structure of the Earth and the nature of seismic wave propagation with illustrative examples of observations. Many topics are introduced here and then elaborated in the second part which provides a füll development of the theoretical background. This material is then drawn upon in Volume II, which is concerned with seismic observations at different distance ranges from the source and the way in which the seismic wavefield across the globe evolves with distance.

The emphasis throughout is on waves in seismological applications, and the selection of methods and techniques is designed to provide physical insight rather than concentrate on numerical efficiency.