An Introduction to Geophysical Exploration

This is the third edition of this established textbook, which has become the standard introduction to geophysics for many earth science students. The book is exactly what it claims to be: an introductory text aimed at a wide readership, with the mathematics kept to an absolute minimum. It is a book that is accessible to geologists and engineers alike as well as geophysics students starting out on their studies. The book is well-written and easy to read and presents numerous examples of the application of geophysics to real problems. This edition includes an additional author, Ian Hill, and the content is updated and expanded, although the colour plates, carried over from the second edition, now look somewhat dated. After a general discussion on the concepts of geophysics, Chapter 2 is an excellent introduction to geophysical data processing. Many other textbooks of a similar genre restrict their discussion solely to an account of seismic data processing without referring to the basic underlying principles of a time or spatial series. Its inclusion in an early chapter stresses the all-pervasive nature of these data processing techniques in all aspects of applied geophysics, especially now that we live in a digital and not an analogue world. Topics covered include digitization, aliasing, spectral analysis, convolution, deconvolution, correlation functions and digital filtering. Seismic methods take up the next 103 pages, as befits the dominance of these techniques in the commercial world. From basic principles of stress and strain the reader is instructed on wave types, their propagation and attenuation, ray paths and the basics of seismic data acquisition systems. Seismic reflection surveying is developed from a discussion of the geometry of ray paths, including the single horizontal reflector, multiple horizontal reflectors and dipping reflectors. Reflection field techniques are brief, but the basics are covered including CMP gathers and the design of detector arrays. The data processing techniques introduced in Chapter 2 are applied to the processing of reflection seismic data resulting in a corrected, filtered and migrated seismic section. 3-D seismic surveys are discussed and two new topics in this edition are 4-D seismic surveys and three component surveys in which the S as well as the P waves are recorded. Six pages are then devoted to seismic reflection interpretation, but this barely scratches the surface of this immense topic. The seismic reflection chapter is closed with a brief discussion of single-channel marine reflection profiling and its use in offshore aggregate assessment and marine engineering site investigations. Seismic refraction techniques are reasonably comprehensive with all the basic concepts covered and there is an introduction to some of the interpretation schemes that are applied. A new topic for this edition is seismic tomography, a method being applied increasingly in engineering site investigations. Potential field methods are dealt with in Chapters 6 and 7. The basic principles of gravity and its measurement are followed by a derivation of gravity anomalies of simple shapes, gravity surveying techniques and data reduction. One omission is a discussion of isostasy; although mentioned in passing this is a subject I would expect to find in an introductory text, especially when considering gravity anomalies over ocean basins and mountain ranges. The remainder of the gravity surveying chapter deals with interpretation and applications. Magnetic surveying is similarly built up from basic concepts, but it is difficult to deal with the extra complexities of the dipolar magnetic field in such a short chapter. Magnetic anomalies are considered by calculating the anomaly of an isolated magnetic pole. I would have liked to have seen the simple expedient of superimposing the induced dipolar field of a near surface body on the geomagnetic vector that explains in a qualitative way the change in shape of magnetic anomaly with magnetic latitude. Magnetic survey instruments, techniques and data reduction are dealt with well and most aspects of interpretation are covered. The direct current electrical methods (resistivity, induced polarization and self potential) are dealt with in Chapter 8. Resistivity methods are covered thoroughly and there is an excellent introduction to current flow in the ground and the derivation of apparent resistivity. Vertical electrical soundings and resistivity profiling are discussed and the ambiguities of interpretation are well presented. My one criticism is that electrical imaging, which is being used extensively in environmental geophysics, is only mentioned in passing and only with reference to a Wenner array. The remainder of Chapter 8 deals with the basics of induced polarization and self potential. An account of electromagnetic methods in a qualitative textbook is always a difficult task, but a valiant attempt is made in Chapter 9. Surveying techniques are grouped into tilt-angle methods, phase measuring systems and time-domain EM. Non-contacting ground conductivity measurements, which are widely used in shallow investigations, are covered in a dedicated section. Other topics briefly covered include airborne EM, telluric and magnetotelluric methods. Chapter 9 concludes with ground penetrating radar in a section expanded from that in the second edition. However it is still a short section for such a widely used technique that probably deserves greater coverage even in an introductory text. The rudiments of radiometric surveying are covered in Chapter 10 and the book concludes with a chapter on borehole logging that serves as a good introduction to this subject. At the target readership of this book, it is an undoubted success. Within its 262 pages is a wealth of information that either provides the reader with the explanation they require or includes a reference to a higher-level text. The book is of sufficient length to allow most methods to be explored in some depth, but without it becoming a weighty-tome that the occasional reader would find daunting. I have no qualms in recommending this book to those seeking background information on applied geophysics or for those new to the subject. This review is published with the permission of the Executive Director of the British Geological Survey (NERC).