In order to keep pace with the continuing development of geophysical exploration methods, the sixth volume in this series concentrates on topical subjects that the working geophysicist may be called upon to implement or test.

The practising geophysicist is often called upon to investigate problems in the sub-surface which require methods not wholly familiar. There is a great range of such problems, and often a range of methods which could be applied.

One facet of development in this field is that the methods of gathering and processing geophysical data, and displaying results, lead to presentations which are more and more comprehensible geologically. Expressed in another way, the work of the interpreter becomes progressively less onerous. The contributions in this collection of original papers illustrate this direction of development, especially in seismic prospecting. If one could carry out to perfection the steps of spiking deconvolution, migration and time--depth conversion, then the seismic section would be as significant geologically as a cliff-face, and as easy to understand. Perhaps this is not yet achieved, but it remains an objective, brought closer by work such as that described by the authors. The editor offers his best thanks to the contributors-busy geophysicists who have written with erudition on this range of subjects of current interest. A. A. FITCH v CONTENTS Preface v List of Contributors IX 1. Determination of Static Corrections A. W. ROGERS 2. Vibroseis Processing 37 P. KIRK The 11 Norm in Seismic Data Processing 53 3. H. L. TAYLOR 4. Predictive Deconvolution 77 E. A. ROBINSON 5. Exploration for Geothermal Energy 107 G. V. KELLER 6. Migration 151 P. HOOD Index 231 vii LIST OF CONTRIBUTORS P. HOOD Geophysicist, Geophysics Research Branch, The British Petroleum Co. Ltd, Britannic House, Moor Lane, London EC2Y 9BU, UK.

This is a collection of original papers, each by an expert in his field. They deal with different sectors of recent geophysical development. It may be, at first, difficult to see what else unites them, and how these several technologies can contribute to an integrated exploration process. What brings these writers together is that they have all contributed to the improvement of what comes to the eye of the geophysical interpreter. Some of the improvement is achieved at the data-gathering stage, some of it in processing, and in presentation. For all of this improvement interpreters in general are most grateful. The editor is appreciative in a quite personal way, not only of the advances in technology, but also of the effort in writing which has been made by these busy contributors, and so created this collection. Something can be said here about interpretation and the environment in which it is carried out, since it represents the field where the results of these technical developments are ultimately tested. In the commercial world it is from the geophysical interpreter that management learns the results of a large sector of exploration expenditure, and learns them in a form on which still larger expenditures on later phases of exploration can be based.

One of the themes in current geophysical development is the bringing together of the results of observations made on the surface and those made in the subsurface. Several benefits result from this association. The detailed geological knowledge obtained in the subsurface can be extrapolated for short distances with more confidence when the geologi cal detail has been related to well-integrated subsurface and surface geophysical data. This is of value when assessing the characteristics of a partially developed petroleum reservoir. Interpretation of geophysical data is generally improved by the experience of seeing the surface and subsurface geophysical expression of a known geological configuration. On the theoretical side, the understanding of the geophysical processes themselves is furthered by the study of the phenomena in depth. As an example, the study of the progress of seismic wave trains downwards and upwards within the earth has proved most instructive. This set of original papers deals with some of the more vigorous developments in subsurface geophysics: and it is hoped that it will contribute to the understanding of geophysical phenomena in the solid. The editor thanks the busy workers in the several fields who have made time to produce these contributions."

Geophysical prospecting is an applied science and the range of scientific principles to be applied is very wide. In this collection of original papers, the application of many different principles is described in the search for sulphides, other metallic ores and radioactive deposits. The papers are all concerned with surface observations and cover both the theory and the practice of the methods used. In all cases the advan tages and disadvantages of the methods are described and their role in the detection of mineral deposits is discussed and placed in context. Electromagnetic methods are covered in detail, involving the use of both electric and magnetic field effects. Techniques are described involv ing observations both at a number of discrete frequencies and with continuously changing frequency. In spite of the diversity of method it is interesting to note the strong links between the papers; two chapters, for example, start from the same fundamental illustration, first published by Won, of the basic relationship between source frequency, ground con ductivity and depth of penetration. The all-important economic aspects are not forgotten and the first chapter assesses the statistics of performance and describes their use in the shaping and management of an exploration programme. The editor takes this opportunity to thank the busy men who have set aside time to write these contributions."