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Summary
Summary
This new edition of the well-established Kearey and Brooks text is fully updated to reflect the important developments in geophysical methods since the production of the previous edition. The broad scope of previous editions is maintained, with even greater clarity of explanations from the revised text and extensively revised figures. Each of the major geophysical methods is treated systematically developing the theory behind the method and detailing the instrumentation, field data acquisition techniques, data processing and interpretation methods. The practical application of each method to such diverse exploration applications as petroleum, groundwater, engineering, environmental and forensic is shown by case histories.
The mathematics required in order to understand the text is purposely kept to a minimum, so the book is suitable for courses taken in geophysics by all undergraduate students. It will also be of use to postgraduate students who might wish to include geophysics in their studies and to all professional geologists who wish to discover the breadth of the subject in connection with their own work.
Author Notes
Philip Kearey gained a B.Sc. in Geology and a Ph.D. in Geophysics at the University of Durham. After two years working for the Canadian government he took up a post as Lecturer in Applied Geophysics at the University of Bristol in 1976. He was promoted to Senior Lecturer in 1995. He was elected as Chartered Geologist of the Geological Society in 1991.
Mike Brooks was a Professor of Geology and Head of the Department of Geology at Cardiff University from 1978 to 1993 and is now a Professor Emeritus of the University. From 1993 to 2001 he was the Education and Training Officer of the Geological Society of London.
Ian Hill is Senior Lecturer in Geophysics at the University of Leicester where he teaches Geophysics and Plate Tectonics. He was the first chairman of the Environmental and Industrial Geophysics Group (EIGG) of the Geological Society of London. He is a Chartered Geologist.
Table of Contents
Preface | p. ix |
1 The principles and limitations of geophysical exploration methods | p. 1 |
1.1 Introduction | p. 1 |
1.2 The survey methods | p. 1 |
1.3 The problem of ambiguity in geophysical interpretation | p. 6 |
1.4 The structure of the book | p. 7 |
2 Geophysical data processing | p. 8 |
2.1 Introduction | p. 8 |
2.2 Digitization of geophysical data | p. 8 |
2.3 Spectral analysis | p. 10 |
2.4 Waveform processing | p. 13 |
2.4.1 Convolution | p. 13 |
2.4.2 Deconvolution | p. 16 |
2.4.3 Correlation | p. 16 |
2.5 Digital filtering | p. 17 |
2.5.1 Frequency filters | p. 18 |
2.5.2 Inverse (deconvolution) filters | p. 19 |
2.6 Imaging and modelling | p. 19 |
Problems | p. 20 |
Further reading | p. 20 |
3 Elements of seismic surveying | p. 21 |
3.1 Introduction | p. 21 |
3.2 Stress and strain | p. 21 |
3.3 Seismic waves | p. 22 |
3.3.1 Body waves | p. 23 |
3.3.2 Surface waves | p. 24 |
3.3.3 Waves and rays | p. 25 |
3.4 Seismic wave velocities of rocks | p. 26 |
3.5 Attenuation of seismic energy along ray paths | p. 27 |
3.6 Ray paths in layered media | p. 28 |
3.6.1 Reflection and transmission of normally incident seismic rays | p. 28 |
3.6.2 Reflection and refraction of obliquely incident rays | p. 30 |
3.6.3 Critical refraction | p. 31 |
3.6.4 Diffraction | p. 31 |
3.7 Reflection and refraction surveying | p. 32 |
3.8 Seismic data acquisition systems | p. 33 |
3.8.1 Seismic sources and the seismic/acoustic spectrum | p. 34 |
3.8.2 Seismic transducers | p. 39 |
3.8.3 Seismic recording systems | p. 41 |
Problems | p. 42 |
Further reading | p. 42 |
4 Seismic reflection surveying | p. 43 |
4.1 Introduction | p. 43 |
4.2 Geometry of reflected ray paths | p. 43 |
4.2.1 Single horizontal reflector | p. 43 |
4.2.2 Sequence of horizontal reflectors | p. 45 |
4.2.3 Dipping reflector | p. 46 |
4.2.4 Ray paths of multiple reflections | p. 47 |
4.3 The reflection seismogram | p. 48 |
4.3.1 The seismic trace | p. 48 |
4.3.2 The shot gather | p. 49 |
4.3.3 The CMP gather | p. 50 |
4.4 Multichannel reflection survey design | p. 51 |
4.4.1 Vertical and horizontal resolution | p. 52 |
4.4.2 Design of detector arrays | p. 53 |
4.4.3 Common mid-point (CMP) surveying | p. 54 |
4.4.4 Display of seismic reflection data | p. 57 |
4.5 Time corrections applied to seismic traces | p. 57 |
4.6 Static correction | p. 57 |
4.7 Velocity analysis | p. 59 |
4.8 Filtering of seismic data | p. 61 |
4.8.1 Frequency filtering | p. 62 |
4.8.2 Inverse filtering (deconvolution) | p. 62 |
4.8.3 Velocity filtering | p. 65 |
4.9 Migration of reflection data | p. 67 |
4.10 3D seismic reflection surveys | p. 72 |
4.11 Three component (3C) seismic reflection surveys | p. 76 |
4.12 4D seismic reflection surveys | p. 77 |
4.13 Vertical seismic profiling | p. 79 |
4.14 Interpretation of seismic reflection data | p. 80 |
4.14.1 Structural analysis | p. 81 |
4.14.2 Stratigraphical analysis (seismic stratigraphy) | p. 82 |
4.14.3 Seismic modelling | p. 84 |
4.14.4 Seismic attribute analysis | p. 85 |
4.15 Single-channel marine reflection profiling | p. 86 |
4.15.1 Shallow marine seismic sources | p. 89 |
4.15.2 Sidescan sonar systems | p. 90 |
4.16 Applications of seismic reflection surveying | p. 92 |
Problems | p. 97 |
Further reading | p. 98 |
5 Seismic refraction surveying | p. 99 |
5.1 Introduction | p. 99 |
5.2 Geometry of refracted ray paths: planar interfaces | p. 99 |
5.2.1 Two-layer case with horizontal interface | p. 100 |
5.2.2 Three-layer case with horizontal interface | p. 101 |
5.2.3 Multilayer case with horizontal interfaces | p. 102 |
5.2.4 Dipping-layer case with planar interfaces | p. 102 |
5.2.5 Faulted planar interfaces | p. 104 |
5.3 Profile geometries for studying planar layer problems | p. 105 |
5.4 Geometry of refracted ray paths: irregular (non-planar) interfaces | p. 106 |
5.4.1 Delay time | p. 106 |
5.4.2 The plus-minus interpretation method | p. 108 |
5.4.3 The generalized reciprocal method | p. 109 |
5.5 Construction of wavefronts and ray-tracing | p. 110 |
5.6 The hidden and blind layer problems | p. 110 |
5.7 Refraction in layers of continuous velocity change | p. 112 |
5.8 Methodology of refraction profiling | p. 112 |
5.8.1 Field survey arrangements | p. 112 |
5.8.2 Recording scheme | p. 113 |
5.8.3 Weathering and elevation corrections | p. 114 |
5.8.4 Display of refraction seismograms | p. 115 |
5.9 Other methods of refraction surveying | p. 115 |
5.10 Seismic tomography | p. 117 |
5.11 Applications of seismic refraction surveying | p. 119 |
5.11.1 Engineering and environmental surveys | p. 119 |
5.11.2 Hydrological surveys | p. 120 |
5.11.3 Crustal seismology | p. 120 |
5.11.4 Two-ship seismic surveying: combined refraction and reflection surveying | p. 122 |
Problems | p. 123 |
Further reading | p. 124 |
6 Gravity surveying | p. 125 |
6.1 Introduction | p. 125 |
6.2 Basic theory | p. 125 |
6.3 Units of gravity | p. 126 |
6.4 Measurement of gravity | p. 126 |
6.5 Gravity anomalies | p. 129 |
6.6 Gravity anomalies of simple-shaped bodies | p. 130 |
6.7 Gravity surveying | p. 132 |
6.8 Gravity reduction | p. 133 |
6.8.1 Drift correction | p. 133 |
6.8.2 Latitude correction | p. 133 |
6.8.3 Elevation corrections | p. 134 |
6.8.4 Tidal correction | p. 136 |
6.8.5 Eotvos correction | p. 136 |
6.8.6 Free-air and Bouguer anomalies | p. 136 |
6.9 Rock densities | p. 137 |
6.10 Interpretation of gravity anomalies | p. 139 |
6.10.1 The inverse problem | p. 139 |
6.10.2 Regional fields and residual anomalies | p. 139 |
6.10.3 Direct interpretation | p. 140 |
6.10.4 Indirect interpretation | p. 142 |
6.11 Elementary potential theory and potential field manipulation | p. 144 |
6.12 Applications of gravity surveying | p. 147 |
Problems | p. 150 |
Further reading | p. 153 |
7 Magnetic surveying | p. 155 |
7.1 Introduction | p. 155 |
7.2 Basic concepts | p. 155 |
7.3 Rock magnetism | p. 158 |
7.4 The geomagnetic field | p. 159 |
7.5 Magnetic anomalies | p. 160 |
7.6 Magnetic surveying instruments | p. 162 |
7.6.1 Introduction | p. 162 |
7.6.2 Fluxgate magnetometer | p. 162 |
7.6.3 Proton magnetometer | p. 163 |
7.6.4 Optically pumped magnetometer | p. 164 |
7.6.5 Magnetic gradiometers | p. 164 |
7.7 Ground magnetic surveys | p. 164 |
7.8 Aeromagnetic and marine surveys | p. 164 |
7.9 Reduction of magnetic observations | p. 165 |
7.9.1 Diurnal variation correction | p. 165 |
7.9.2 Geomagnetic correction | p. 166 |
7.9.3 Elevation and terrain corrections | p. 166 |
7.10 Interpretation of magnetic anomalies | p. 166 |
7.10.1 Introduction | p. 166 |
7.10.2 Direct interpretation | p. 168 |
7.10.3 Indirect interpretation | p. 170 |
7.11 Potential field transformations | p. 172 |
7.12 Applications of magnetic surveying | p. 173 |
Problems | p. 180 |
Further reading | p. 181 |
8 Electrical surveying | p. 183 |
8.1 Introduction | p. 183 |
8.2 Resistivity method | p. 183 |
8.2.1 Introduction | p. 183 |
8.2.2 Resistivities of rocks and minerals | p. 183 |
8.2.3 Current flow in the ground | p. 184 |
8.2.4 Electrode spreads | p. 186 |
8.2.5 Resistivity surveying equipment | p. 186 |
8.2.6 Interpretation of resistivity data | p. 187 |
8.2.7 Vertical electrical sounding interpretation | p. 188 |
8.2.8 Constant separation traversing interpretation | p. 193 |
8.2.9 Limitations of the resistivity method | p. 196 |
8.2.10 Applications of resistivity surveying | p. 196 |
8.3 Induced polarization (IP) method | p. 199 |
8.3.1 Principles | p. 199 |
8.3.2 Mechanisms of induced polarization | p. 199 |
8.3.3 Induced polarization measurements | p. 200 |
8.3.4 Field operations | p. 201 |
8.3.5 Interpretation of induced polarization data | p. 201 |
8.3.6 Applications of induced polarization surveying | p. 202 |
8.4 Self-potential (SP) method | p. 203 |
8.4.1 Introduction | p. 203 |
8.4.2 Mechanism of self-potential | p. 203 |
8.4.3 Self-potential equipment and survey procedure | p. 203 |
8.4.4 Interpretation of self-potential anomalies | p. 204 |
Problems | p. 205 |
Further reading | p. 207 |
9 Electromagnetic surveying | p. 208 |
9.1 Introduction | p. 208 |
9.2 Depth of penetration of electromagnetic fields | p. 208 |
9.3 Detection of electromagnetic fields | p. 209 |
9.4 Tilt-angle methods | p. 209 |
9.4.1 Tilt-angle methods employing local transmitters | p. 210 |
9.4.2 The VLF method | p. 210 |
9.4.3 The AFMAG method | p. 212 |
9.5 Phase measuring systems | p. 212 |
9.6 Time-domain electromagnetic surveying | p. 214 |
9.7 Non-contacting conductivity measurement | p. 216 |
9.8 Airborne electromagnetic surveying | p. 218 |
9.8.1 Fixed separation systems | p. 218 |
9.8.2 Quadrature systems | p. 220 |
9.9 Interpretation of electromagnetic data | p. 221 |
9.10 Limitations of the electromagnetic method | p. 221 |
9.11 Telluric and magnetotelluric field methods | p. 221 |
9.11.1 Introduction | p. 221 |
9.11.2 Surveying with telluric currents | p. 222 |
9.11.3 Magnetotelluric surveying | p. 224 |
9.12 Ground-penetrating radar | p. 225 |
9.13 Applications of electromagnetic surveying | p. 227 |
Problems | p. 228 |
Further reading | p. 230 |
10 Radiometric surveying | p. 231 |
10.1 Introduction | p. 231 |
10.2 Radioactive decay | p. 231 |
10.3 Radioactive minerals | p. 232 |
10.4 Instruments for measuring radioactivity | p. 233 |
10.4.1 Geiger counter | p. 233 |
10.4.2 Scintillation counter | p. 233 |
10.4.3 Gamma-ray spectrometer | p. 233 |
10.4.4 Radon emanometer | p. 234 |
10.5 Field surveys | p. 235 |
10.6 Example of radiometric surveying | p. 235 |
Further reading | p. 235 |
11 Geophysical borehole logging | p. 236 |
11.1 Introduction to drilling | p. 236 |
11.2 Principles of well logging | p. 236 |
11.3 Formation evaluation | p. 237 |
11.4 Resistivity logging | p. 237 |
11.4.1 Normal log | p. 238 |
11.4.2 Lateral log | p. 239 |
11.4.3 Laterolog | p. 240 |
11.4.4 Microlog | p. 241 |
11.4.5 Porosity estimation | p. 241 |
11.4.6 Water and hydrocarbon saturation estimation | p. 241 |
11.4.7 Permeability estimation | p. 242 |
11.4.8 Resistivity dipmeter log | p. 242 |
11.5 Induction logging | p. 243 |
11.6 Self-potential logging | p. 243 |
11.7 Radiometric logging | p. 244 |
11.7.1 Natural gamma radiation log | p. 244 |
11.7.2 Gamma-ray density log | p. 244 |
11.7.3 Neutron-gamma-ray log | p. 245 |
11.8 Sonic logging | p. 246 |
11.9 Temperature logging | p. 247 |
11.10 Magnetic logging | p. 247 |
11.10.1 Magnetic log | p. 247 |
11.10.2 Nuclear magnetic resonance log | p. 247 |
11.11 Gravity logging | p. 247 |
Problems | p. 248 |
Further reading | p. 249 |
Appendix SI, c.g.s. and Imperial (customary USA) units and conversion factors | p. 250 |
References | p. 251 |
Index | p. 257 |