Seismic waves – generated both by natural earthquakes and by man-made sources – have produced an enormous amount of information about the Earth's interior. In classical seismology, the Earth is modeled as a sequence of uniform horizontal layers (or sperical shells) having different elastic properties and one determines these properties from travel times and dispersion of seismic waves. The Earth, however, is not made of horizontally uniform layers, and classic seismic methods can take large-scale inhomogeneities into account. Smaller-scale irregularities, on the other hand, require other methods. Observations of continuous wave trains that follow classic direct S waves, known as coda waves, have shown that there are heterogeneities of random size scattered randomly throughout the layers of the classic seismic model. This book focuses on recent developments in the area of seismic wave propagation and scattering through the randomly heterogeneous structure of the Earth, with emphasis on the lithosphere. The presentation combines information from many sources to present a coherent introduction to the theory of scattering in acoustic and elastic materials and includes analyses of observations using the theoretical methods developed.

Reprint from Pure and Applied Geophysics (PAGEOPH), Volume 131 (1989), No. 4

Reprint from Pure and Applied Geophysics (PAGEOPH), Volume 128 (1988), No. 1/2

Consisting of more than 150 articles written by leading experts, this authoritative reference encompasses the entire field of solid-earth geophysics. It describes in detail the state of current knowledge, including advanced instrumentation and techniques, and focuses on important areas of exploration geophysics. It also offers clear and complete coverage of seismology, geodesy, gravimetry, magnetotellurics and related areas in the adjacent disciplines of physics, geology, oceanography and space science.

Earthquakes come and go as they please, leaving behind them trails of destruc tion and casualties. Although their occurrence is little affected by what we do or think, it is the task of earth scientists to keep studying them from all possible angles until ways and means are found to divert, forecast, and eventually control them. In ancient times people were awestruck by singular geophysical events, which were attributed to supernatural powers. It was recognized only in 1760 that earthquakes originated within the earth. A hundred years later, first systematic attempts were made to apply physical principles to study them. During the next century scientists accumulated knowledge about the effects of earthquakes, their geographic patterns, the waves emitted by them, and the internal constitution of the earth. During the past 20 years, seismology has made a tremendous progress, mainly because of the advent of modern computers and improvements in data acquisi tion systems, which are now capable of digital and analog recording of ground motion over a frequency range of five orders of magnitude. These technologic developments have enabled seismologists to make measurements with far greater precision and sophistication than was previously possible. Advanced computational analyses have been applied to high-quality data and elaborate theoretical models have been devised to interpret them. As a result, far reaching advances in our knowledge of the earth's structure and the nature of earthquake sources have occurred.

Seismic measurements take many forms, and appear to have a universal role in the Earth Sciences. They are the means for most easily and economically interpreting what lies beneath the visible surface. There are huge economic rewards and losses to be made when interpreting the shallow crust or subsurface more, or less accurately, as the case may be.