Principles of AppliedGeophysics

Fifth edition

D.S. Parasnis

Professor emeritus of Applied GeophysicsDepartment of Applied Geophysics,

University ofLuled,Lulea, Sweden

Fellow of the Royal Swedish Academy of Engineering Sciences

CHAPMAN & HALLLondon • Weinheim • New York • Tokyo • Melbourne • Madras

Contents

PagesPreface xi

1 Introduction 1

2 Magnetic methods 42.1 Short history 42.2 Basic concepts and units • 42.3 Magnetic properties 72.4 The geomagnetic field 122.5 Instruments of magnetic surveying 142.6 Survey layout and field procedure 182.7 Relative merits of horizontal-, vertical- and total-field measurements 202.8 Qualitative interpretation of magnetic anomalies 212.9 Quantitative interpretation 272.10 Effect of demagnetization 522.11 Further examples of magnetic investigations 54

Problems 58 .

3 Gravitational methods 603.1 Introduction 603.2 Gravitational field of the Earth 623.3 Measurement of gravity: absolute and relative measurements 643.4 Gravimeters 653.5 Field procedure 673.6 Corrections to gravity observations 683.7 The Bouguer anomaly 723.8 Density determinations 733.9 Interpretation 733.10 Depth determinations 813.11 Some theoretical aspects of gravity interpretation 843.12 Determination of total anomalous mass 913.13 Derivatives of gravity 923.14 Illustrations of gravity surveys and interpretation 96

CONTENTS

3.15 Note on marine gravity measurements 100Problems 102

4 Electrical methods 1044.1 Introduction 1044.2 Self-potential method 1044.3 Earth resistivity 1214.4 Some practical aspects of resistivity work 1244.5 Vertical electrical sounding 1314.6 Electrical mapping 1554.7 Anisotropic Earth 172

Problems 176

5 Induced polarization 1795.1 Introduction 1795.2 Measures of induced polarization 1805.3 Origin of induced polarization 1845.4 Response of polarizable bodies 1875.5 Electromagnetic coupling 1885.6 Negative induced polarization 1905.7 Induced polarization soundings for groundwater problems 191

Problems 1930

6 Electromagnetic methods 1946.1 Introduction 1946.2 Electromagnetic induction 1956.3 Elliptic polarization 1996.4 Free-space magnetic fields of low-frequency sources 2016.5 Quasi-static, near and far fields 2046.6 Classification of artificial-source, continuous-wave methods 2066.7 Near-field continuous-wave methods 2076.8 Far-field methods , 2206.9 Interpretation aids in electromagnetic prospecting v 2296.10 Depth penetration 2326.11 Influence of overburden conductivity and current channelling 2336.12 Transient-field methods (time-domain electromagnetism) 2356.13 Influence of magnetic permeability 2416.14 Controlled-source electromagnetic sounding 2436.15 Ground-penetrating radar . 2466.16 Natural-field methods 2626.17 Airborne measurements 2666.18 Note on the design of electromagnetic coils 269

Problems 271

7 Seismic methods 2737.1 Introduction 2737.2 Elastic constants and waves 2737.3 The reflection method 281

CONTENTS

7.4 The refraction method 329Problems 343

8 Radioactivity methods 3458.1 Introduction 3458.2 Theoretical background 3458.3 Radioactivity of rocks 3488.4 Radiation detectors, measurement units and field procedure 3488.5 Radon measurements 3528.6 Radioactive density determinations 3548.7 Airborne radioactivity measurements 355

9 Outline of well logging in oil fields 3569.1 Introduction 3569.2 Permeable zones 3569.3 Archie's law 3579.4 Permeability-zone logs 3589.5 Resistivity and conductivity logs 3609.6 Porosity logs 3629.7 Auxiliary logs and measurements 3679.8 Basic log interpretation procedure 367

10 Miscellaneous methods and topics , 36910.1 Borehole magnetometer 36910.2 Mise-d-la-masse method 36910.3 Logging in crystalline rocks and coal fields 37110.4 Geothermal methods 37110.5 Geochemical prospecting 37110.6 Optimum point and line spacing 37210.7 Position location in airborne surveying 37310.8 Composite or integrated surveys 37410.9 Frequency or wavenumber filtering 377

Appendices - 386Appendix 1 The magnetic potential 386Appendix 2 Magnetized sphere and a magnetic dipole 389Appendix 3 Magnetic anomaly of a sphere 392Appendix 4 Measurement of susceptibility and remanence 393Appendix 5 Magnetic potential of a linear dipole and the anomalies of thin

and thick sheets, and of a geological fault 396Appendix 6 Demagnetization 'factors' for a rectangular parallelepiped 402Appendix 7 Electric potential 404Appendix 8 Apparent resistivities for dipole-dipole configurations 405Appendix 9 Potential of a point current electrode on the surface of

a horizontally layered Earth 406Appendix 10 Homogeneous, anisotropic Earth (derivation of equation (4.76)) 409Appendix 11 Single-turn loop and other topics in electromagnetic methods 410Appendix 12 Acoustic impedance 413Appendix 13 Fourier transforms and convolution 414

CONTENTS

Answers and hints 419

References 422

Index 431