LETTER TO THE EDITOR

finite-difference method being described in the book. The merits and disadvantages of each are summarized, and the authors point out that what is best for one set of data may not be the best for another. A large proportion of the effort involved in bringing an idea to the stage where it can be used commercially as a computer programme lies in the software design. This is only briefly touched uponat the end of the chapter, where a typical sequence of events followed during processing is outlined. As an addendum to the data processing chapter, a chapter giving derivations and proofs of equations is helpful for the mathematically inclined reader. It may, however, be overlooked without losing the overall thread of the book. Nomenclature throughout is consistent and unambiguous. The third part of the book is devoted to the geologic interpretation of reflection data. The deepest reflections normally considered in oil exploration come from about 10 km depth, and sufficient resolution can often be obtained to allow a three dimensional stratigraphic model of an area to be constructed. The authors describe a range of geologic structures and relate these to their expression on a seismic section. Examples are reefs, salt and shale flow structures and types of faulting. Pitfalls that can trap the geophysicist are given consideration, and the importance of using data from as many sources as possible, such as borehole logs, magnetic and gravity surveys etc., in conjunction with seismic reflection is emphasized. Synthetic seismograms and the effects of lateral velocity variations are also discussed. The book will be of value principally to the practising exploration geophysicist and specialized student. The relevance of reflection seismology, which forms the basis of Volume 2, to the earthquake seismologist is really limited to identification of active faults. If there is a question as to which of several apparent surface fault breaks is the actual expression of an active fault, then reflection seismics might be able to provide the answer. The techniques used in processing reflection data concentrate on improving resolution and signal-to-noise ratio, whereas the earthquake seismologist may be detecting events with sources possibly thousands of miles away, and he will be primarily interested in the character of those sources. The analyses of these two widely different processes are clearly very dissimilar. Nonetheless, the earthquake seismologist may find much of interest of the two volumes comprising Exploration SeismoZogy, which together provide a comprehensive and readable account of this broad subject.