BOOK REVIEWS

Principles of Applied Geophysics (Fifth Edition), D.S. Parasnis, Prentice and Hall,437 pp, £39.99, 1997.

Here, 35 years after the original, is a new edition of one of the few comprehensivetextbooks of applied or ‘exploration’ geophysics. The work has become a standardfor university teaching but, within the compass of 400-odd pages, such a book isincreasingly a difficult task to fulfil. In particular, the principles and practice ofthe seismic method, pre-eminent in oil exploration and production, now demandwhole textbooks of their own and their practitioners sometimes even threaten toclaim exclusive rights to the word ‘geophysics’ itself. Here, in this work, seis-mic methods occupy only one of the ten (approximately equally-sized) chapters,giving the book a particular appeal to those interested in the multitude of othermethods (including modest seismic surveys for shallow investigations) which findwidespread application in mineral and groundwater exploration, environmental andengineering studies and archaeology.

Professor Parasnis’ approach is firmly rooted in the physics and mathematicsof the subject which will add to its appeal for students coming to geophysics fromthe pure physical sciences. However, their understanding of geology and the de-scriptive and qualitative aspects of interpreting geophysical data in sympathy withgeological and other information will require reading beyond these covers.

The chapters are entitled Introduction, Magnetic methods, Gravitational meth-ods, Electrical methods, Induced polarisation, Electromagnetic methods, Seismicmethods, Radioactivity methods, Outline of well-logging in oil fields, Miscella-neous methods and topics and are followed by 13 largely mathematical appendices.The general pattern is to establish for each method the theory, describe the instru-mentation and then to derive equations to the anomalies that can be calculated oversimple geometrical bodies from this theory. Justifiably, the temptation to describeinstrumentation of only historic significance has been resisted, though there isunfortunately little consideration given to normal survey practice for most methods.

For example, many of the survey methods can be operated from aircraft forrapid reconnaissance of large areas at low cost. Aeromagnetic surveys are theprimary example. But all the technology and craftsmanship necessary for so doingare dismissed in a short paragraph. The currently operational status of airborneand satellite gravimetry does not receive a mention. The success of the airbornegamma-ray spectrometer in recent years as a geological mapping tool is not to befound in the half page devoted to this method and the reader is offered only one

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reference from 1973 for further reading. The revolution in survey practice broughtabout by global positioning systems (GPS) in the 1990s is similarly accorded but abrief paragraph and a single reference from 1986.

A fairly extended treatment of ground-penetrating radar is the main addition tothis edition and occupies some 16 pages. Elsewhere, sections on micromagneticsand microgravity methods have been introduced since the fourth edition (1986) aswell as a treatment of gravity derivatives and continuations, interpretation proce-dures for self- potential and induced polarisation applied to salt-water intrusion, aswell as a revised section on seismic interpretation.

The fundamental issue of sampling, i.e. collecting sufficient point observationsin thex,y plane to faithfully reconstruct the continuous physical field over a surveyarea, is dealt with only in the classical one-dimensional context of digital seismictraces. The quality of well-sampled surveys in thex,y plane and their represen-tation as images, borrowing the technology of image processing which has hadsuch enormous impact on geophysical surveys in the last decade, is illustrated by asingle grey-scale example of distinctly inferior quality. Even so, the theory set outin Sections 10.6 and 10.9 and Appendix 13 is highly relevant to this approach.

Like many later editions of established books, the mould has not really been bro-ken and the excellent, readable approach is still to be recommended for a throughtreatment of the basic theory of applied geophysics. The tried and tested formulacan be relied upon to serve in the future as it has evidently done in the past. Some-thing vibrant and exciting about the late-20th century geophysicist’s ingenuity inusing physical rock properties to develop unparalleled ‘windows’ on the secretsof underground space seems to be missing, however, and recent developments –such a colour imaging and tomography – are not to be found in the text, index orreferences. The references themselves are extensive, but often refer only to datedsource material rather than recent reviews of current practice. Scarcely 10 percentof them are less than ten years old, helping to lend the aura of an earlier epoch tothe work as a whole.

We are warned at the outset in a quotation from Leonardo da Vinci: “This ispractice, but remember first to set forth the theory”. The theory and the principlesare set forth clearly, as promised also in the title. We learn much less of the practice.The aspiring graduate might find little to excite his or her ambition for a careerof professional practice in a dynamic, fast-moving and evolving profession, everanxious to exploit the advantages of new technology. But the profession must begrateful that Parasnis has the ability, opportunity and determination to sustain hiscontribution to the literature on the physical and mathematical basis of it all whilethe majority are busy with perhaps more exciting but certainly less durable pursuits.

Colin ReevesDelft