Looking into the Earth: An Introduction to Geological Geophysics

by Alan E. Mussett , M. Aftab Khan , Illustrated by Sue Button

• ISBN13: 9780521785747
• ISBN10: 052178574X
• Format: Paperback
• Copyright: 2000-10-23
• Publisher: Cambridge University Press

Summary

Looking Into the Earth comprehensively describes the principles and applications of both 'global’ and 'exploration’ geophysics on all scales. It forms an introduction to geophysics suitable for those who do not necessarily intend to become professional geophysicists, including geologists, civil engineers, environmental scientists, and field archaeologists. The book is organised into two parts: Part 1 describes the geophysical methods, while Part 2 illustrates their use in a number of extended case histories. Mathematical and physical principles are introduced at an elementary level, and then developed as necessary. Student questions and exercises are included at the end of each chapter. The book is aimed primarily at introductory and intermediate university students taking courses in geology, earth science, environmental science, and engineering. It will also form an excellent introductory textbook in geophysics departments, and will help practising geologists, archaeologists and engineers understand what geophysics can offer their work.

Table of Contents

Preface: Turning a Magician into an Expert	xvii
Acknowledgements	xix
Introducing Geophysics and This Book	1	(6)
What is geophysics?	1	(1)
The Earth through geophysical spectacles: The relation of geophysics to geology	2	(1)
What this book covers and how it is structured	2	(5)
Summary	3	(1)
Further reading	4	(3)
Part I GEOPHYSICAL METHODS
Data Acquisition and Processing	7	(1)
Data Acquisition and Reduction: Carrying out a Geophysical Survey	7	(6)
Data acquisition: Taking measurements	7	(1)
Data reduction	8	(1)
Signal and noise	8	(1)
Modelling	9	(1)
Geological interpretation	10	(1)
Displaying the results	10	(3)
Summary	11	(1)
Further reading	12	(1)
Problems	12	(1)
Data Processing: Getting More Information from the Data	13	(11)
Fourier analysis	13	(4)
Wavelength	13	(1)
Harmonic analysis	14	(1)
Fourier analysis of a profile	15	(1)
Fourier analysis in 2D: Gridded data	16	(1)
Why a harmonic series?	16	(1)
Digital filtering	17	(4)
Simple filters	17	(1)
Aliasing	18	(2)
Designing a simple filter	20	(1)
Filtering in 2D: Gridded data	20	(1)
Using filters to enhance various types of features	21	(1)
Summing up: Fourier analysis and filtering	21	(3)
Summary	22	(1)
Further reading	22	(1)
Problems	22	(2)
Seismology	24	(1)
Global Seismology and Seismic Waves	24	(18)
Waves, pulses, and rays	24	(2)
Detecting seismic waves: Seismometers and geophones	26	(2)
The Earth is concentrically layered	28	(1)
Spherical symmetry of the Earth's interior	28	(1)
Concentric layering	29	(1)
Finding the path of a ray through the Earth	29	(3)
Refraction: Snell's law	29	(1)
Tracing rays through the Earth: The ray parameter, p	30	(1)
Ray tracing and the Earth's velocity-depth structure	31	(1)
Seismic features of the Earth	32	(7)
Core and mantle	32	(1)
Longitudinal and transverse waves	33	(3)
The mantle--core difference	36	(1)
Other seismological features of the Earth	36	(1)
Attenuation	37	(1)
Ray paths in the Earth	37	(2)
Seismic tomography	39	(3)
Summary	39	(1)
Further reading	40	(1)
Problems	40	(2)
Earthquakes and Seismotectonics	42	(23)
What is an earthquake?	42	(1)
Locating an earthquake	43	(1)
Fault-plane solutions and stresses	44	(6)
Fault-plane solutions	44	(5)
The earthquake stress field and the double-couple mechanism	49	(1)
Rupture dimensions and displacements	50	(2)
Measures of earthquake size	52	(2)
Intensity: Severity of an earthquake at a locality	52	(1)
Seismic moment: Size of the earthquake at source	53	(1)
Seismotectonics: Deducing tectonic processes	54	(2)
Qualitative seismotectonics	54	(1)
Quantitative seismotectonics: Seismic and aseismic faulting	55	(1)
Surface waves	56	(1)
Magnitude: Another measure of earthquake strength	57	(3)
Energies of earthquakes	60	(1)
Earthquake damage and its mitigation	60	(5)
Causes of damage	60	(2)
Mitigating the damage caused by earthquakes	62	(1)
Summary	62	(1)
Further reading	63	(1)
Problems	63	(2)
Refraction Seismology	65	(19)
Critical refraction and head waves	65	(2)
Huygens's wavelets	66	(1)
Head waves	67	(1)
The time--distance (t--x) diagram	67	(2)
Multiple layers	69	(1)
Dipping interfaces	70	(2)
Seismic velocities in rocks	72	(1)
Hidden layers	73	(1)
Hidden layer proper	73	(1)
Low-velocity layer	73	(1)
Carrying out a seismic-refraction survey	74	(2)
Undulating interfaces and delay times	76	(3)
Delay times	76	(2)
The plus--minus method	78	(1)
Ray tracing and synthetic seismograms	79	(1)
Detecting offsets in interfaces	80	(1)
Fan shooting: Simple seismic tomography	81	(3)
Summary	81	(1)
Further reading	82	(1)
Problems	82	(2)
Reflection Seismology	84	(23)
Seismic-reflection sections and their limitations	84	(2)
Velocity determination using normal moveout, NMO	86	(1)
Stacking	87	(1)
Dipping reflectors and migration	88	(2)
Faulted reflectors: Diffraction	90	(1)
Multiple reflections	90	(1)
Carrying out a reflection survey	90	(5)
Data acquisition	90	(2)
Common-depth-point (CDP) stacking	92	(1)
Data display	93	(1)
Vibroseis: A nonimpulsive source	94	(1)
What is a reflector?	95	(4)
Strengths of reflected and transmitted pulses	95	(1)
Vertical resolution: The least separation at which interfaces can be distinguished	96	(2)
Synthetic reflection seismograms	98	(1)
Three-dimensional (3D) surveying	99	(1)
Reflection seismology and the search for hydrocarbons	100	(2)
The formation of hydrocarbon traps	100	(1)
The recognition of hydrocarbon traps	101	(1)
Sequence stratigraphy	102	(1)
Shallow-reflection seismic surveys	103	(4)
Summary	104	(1)
Further reading	105	(1)
Problems	105	(2)
Gravity	107	(1)
Gravity on a Small Scale	107	(18)
Newton's Law of Gravitation	107	(2)
The mass of the Earth	109	(1)
Densities of rocks	109	(1)
Gravity units	110	(1)
Gravity anomalies of some bodies	110	(3)
Measuring gravity: Gravimeters	113	(1)
Data reduction	114	(4)
Instrumental effects and other corrections	114	(3)
Residual and regional anomalies	117	(1)
Planning and carrying out a gravity survey	118	(1)
Modelling and interpretation	119	(3)
The inversion problem	119	(2)
Depth rules	121	(1)
Modelling	122	(1)
Total excess mass	122	(1)
Microgravity surveys	122	(3)
Summary	122	(1)
Further reading	123	(1)
Problems	123	(2)
Large-Scale Gravity and Isostasy	125	(14)
Isostasy	125	(9)
The concept of isostasy: Floating blocks	125	(2)
Gravity and isostatic equilibrium	127	(1)
Simple isostatic calculations	127	(3)
Airy and Pratt models of isostasy	130	(1)
Isostasy with regional compensation	131	(1)
The isostatic anomaly	131	(1)
The evidence for isostasy	132	(1)
Isostatic rebound and the viscosity of the asthenosphere	133	(1)
How the mantle is both solid and liquid: Solid-state creep	134	(1)
What is the lithosphere?	135	(1)
Forces on the lithosphere	135	(1)
The shape of the Earth	135	(4)
Seeing the ocean floor in the ocean surface	135	(1)
The large-scale shape of the Earth	136	(1)
Summary	137	(1)
Further reading	137	(1)
Problems	138	(1)
Magnetism	139	(1)
Palaeomagnetism and Mineral Magnetism	139	(23)
The Earth's magnetic field, present and past	139	(3)
Magnets and magnetic fields	139	(1)
The Earth's magnetic field at present	140	(2)
The Earth's magnetic field in the past	142	(1)
Palaeomagnetism	142	(4)
Measuring a palaeomagnetic direction	142	(2)
Palaeopoles, palaeolatitudes, and rotations	144	(1)
Apparent polar wander (APW) paths and relative continental movements	145	(1)
The magnetism of rocks	146	(7)
The atomic nature of magnetisation	146	(1)
Magnetic domains	147	(1)
Curie and blocking temperatures	148	(1)
Thermal remanent magnetisation (TRM)	149	(2)
Magnetic minerals	151	(1)
Mechanisms that magnetise rocks at ambient temperature	152	(1)
Testing when the remanence was acquired	153	(1)
Laboratory tests	153	(1)
Field tests	153	(1)
Magnetostratigraphy	154	(3)
The magnetic polarity timescale	154	(3)
Magnetic polarity stratigraphy	157	(1)
Magnetic stratigraphy utilising secular variation and excursions	157	(1)
Mineral magnetism	157	(1)
Magnetic fabric: Susceptibility anisotropy	158	(4)
Summary	159	(1)
Further reading	160	(1)
Problems	160	(2)
Magnetic Surveying	162	(19)
Magnetic surveying	162	(5)
Anomaly of a buried magnet	162	(1)
Magnetometers	162	(1)
Data acquisition	163	(4)
Data reduction	167	(1)
Anomalies of some simply shaped bodies	167	(3)
Magnetic poles and fields	168	(1)
The field of a dipole	168	(1)
Anomaly of a dipole, or small body	168	(1)
Anomaly of a sphere	169	(1)
Anomaly of a vertical sheet	170	(1)
Depth of the body	170	(2)
Remanent and induced magnetisation	172	(2)
Computer modelling	174	(1)
More advanced processing of data	174	(1)
Reduction to the pole	174	(1)
Pseudogravity	174	(1)
Upward and downward continuation	174	(1)
Magnetic gradiometry	175	(1)
The Blairgowrie magnetic anomaly: A case study	176	(5)
Summary	178	(1)
Further reading	179	(1)
Problems	179	(2)
Electrical	181	(1)
Resistivity Methods	181	(21)
Basic electrical quantities	181	(2)
Resistivity surveying	183	(3)
Resistivities of rocks and minerals	183	(2)
How electricity flows through rocks	185	(1)
The need for four electrodes	185	(1)
Vertical electric sounding, VES: Measuring layered structures	186	(8)
The basic concept	186	(1)
Refraction of current paths	186	(1)
Apparent resistivity	186	(2)
Carrying out a Wenner VES survey	188	(1)
Modelling the data	189	(2)
Other electrode arrays	191	(2)
Limitations of vertical electrical sounding	193	(1)
Resistivity profiling: Detecting lateral variations	194	(3)
Introduction	194	(1)
Some arrays for profiling	195	(2)
Electrical imaging	197	(1)
Designing and interpreting a resistivity survey	198	(4)
Choosing a resistivity array	198	(1)
Geological interpretation	199	(1)
Summary	199	(1)
Further reading	200	(1)
Problems	200	(2)
Induced Polarisation and Self-Potential	202	(8)
Induced polarization, IP	202	(2)
What induced polarization is	202	(1)
Carrying out an IP survey	203	(1)
Data reduction and display	204	(1)
Self-potential, SP	204	(6)
What self-potential is	204	(2)
SP surveying	206	(2)
Summary	208	(1)
Further reading	209	(1)
Problems	209	(1)
Electromagnetic Methods	210	(23)
Basic concepts	210	(1)
Electromagnetic induction	210	(1)
Factors that affect the signal	211	(1)
Some e-m systems	211	(4)
Moving transmitter-plus-receiver system (Slingram)	211	(4)
Turam system	215	(1)
Transient electromagnetic, TEM, systems	215	(2)
The basic concept	215	(1)
The INPUT system	216	(1)
Electromagnetic waves	217	(2)
Wavelengths	217	(1)
Absorption and attenuation of e-m waves	218	(1)
VLF (very-low-frequency) method	219	(2)
Basic concepts	219	(1)
Carrying out a VLF survey	220	(1)
Phase	221	(4)
Magnetotelluric, MT, surveying: Looking into the deep crust and mantle	225	(2)
Basic concepts	225	(2)
Carrying out an MT survey	227	(1)
Ground-penetrating radar, GPR	227	(6)
How ground-penetrating radar works	227	(2)
Velocity, reflection, penetration, and resolution	229	(1)
Data reduction	230	(1)
Uses of GPR surveys	230	(1)
Summary	230	(1)
Further reading	231	(1)
Problems	231	(2)
Radioactivity	233	(1)
The Ages of Rocks and Minerals: Radiometric Dating	233	(28)
The atomic clock	233	(2)
The uranium--lead (U--Pb) dating method	235	(1)
Assumptions of the Basic Dating Equation	236	(1)
The potassium-argon (K-Ar) dating method	236	(5)
The conventional K--Ar method	237	(2)
The argon-argon (Ar--Ar) method	239	(2)
The rubidium--strontium (Rb--Sr) dating method	241	(2)
The samarium--neodymium (Sm--Nd) dating method	243	(1)
The lead--lead (Pb--Pb) dating method	243	(3)
Theory of the method	243	(1)
The `age of the Earth'	244	(2)
Fission-track (FT) dating	246	(1)
What event is being dated?	247	(4)
Diffusion	247	(1)
Closure temperature	248	(1)
Cooling histories	249	(1)
Two dates from a single rock, using the Rb--Sr method	250	(1)
Two dates from a single rock, using the U--Pb discordia method	250	(1)
Dating palaeomagnetism of slowly cooled regions	251	(1)
Dating sedimentary rocks	251	(1)
The geological time scale	251	(1)
Dating young rocks	252	(4)
Uranium-series disequilibrium methods	253	(2)
Carbon-14 (14C) and other dating methods using cosmogenic isotopes	255	(1)
Why so many radiometric dating methods?	256	(5)
Summary	257	(1)
Further reading	258	(1)
Problems	258	(3)
Radioactive Surveying	261	(8)
Radioactive radiations	261	(1)
γ ray surveys	261	(5)
Measurement: The γ ray spectrometer	261	(1)
Carrying out a γ ray survey	262	(2)
Geological mapping	264	(2)
Radon monitoring	266	(3)
Summary	267	(1)
Further reading	267	(1)
Problems	268	(1)
Geothermics	269	(1)
Geothermics: Heat and Temperature in the Earth	269	(16)
Basic ideas in geothermics	269	(3)
Introduction	269	(1)
Temperature and heat	269	(1)
How heat travels: Conduction and convection	270	(1)
Convection and conduction within the Earth	270	(2)
Heat flow and temperature	272	(5)
Measurement of heat flux	272	(1)
Oceanic lithosphere	272	(3)
Continental lithosphere and radioactivity	275	(2)
Effects of changes to the lithosphere	277	(2)
Thermal capacity	277	(1)
Filling of a sedimentary basin	277	(1)
Overthrusting and underthrusting	278	(1)
Crustal thickening and orogenies	278	(1)
Global heat flow and geothermal energy	279	(2)
Global heat flow	279	(1)
Sources of the Earth's heat	279	(1)
Geothermal energy	280	(1)
The effect of surface temperature changes: A record of past climates	281	(4)
Summary	282	(1)
Further reading	283	(1)
Problems	283	(2)
Subsurface Geophysics	285	(1)
Well Logging and Other Subsurface Geophysics	285	(24)
Introduction	285	(1)
Drilling and its effects on the formations	285	(1)
Sources of information from a borehole: Logs	286	(1)
Geophysical well logging in the oil industry	287	(2)
The most commonly used logs	289	(10)
The measurement of strata dip, borehole inclination, and diameter	289	(1)
The self-potential log	290	(1)
Resistivity logs	291	(3)
Radioactivity logs	294	(3)
The sonic log	297	(1)
The temperature log	298	(1)
Cross plots	298	(1)
Geophysical logging outside the oil industry	299	(4)
Mineral exploration	299	(2)
Magnetic logs	301	(1)
The IP--resistivity log	302	(1)
Other well-logging applications	303	(1)
Other subsurface geophysics	303	(6)
Summary	303	(1)
Further reading	304	(1)
Problems	305	(4)
Part II EXAMPLES OF APPLICATIONS
Which Geophysical Methods to Use?	309	(4)
Introduction	309	(1)
Does the problem have geophysical expression?	309	(1)
Is the variation lateral or vertical?	309	(1)
Is the signal detectable?	310	(1)
Will the result be clear enough to be useful?	310	(1)
Is a survey practicable?	311	(2)
Problems	311	(2)
Global Tectonics	313	(32)
The basic concept of plate tectonics	313	(1)
Divergent, or constructive, margins	314	(3)
Ocean-floor magnetic anomalies	314	(1)
The shape of spreading ridges	315	(2)
Conservative margins	317	(3)
Convergent, or destructive, margins	320	(6)
Ocean--ocean convergent margins and subduction zones	321	(3)
Ocean--continent convergent margins	324	(1)
Continent-continent convergent margins	325	(1)
The geometry of plate tectonics	326	(5)
Poles of rotation	326	(2)
Triple junctions and plate evolution	328	(3)
The globe according to plate tectonics	331	(1)
Continental positions in the past	332	(1)
Crust formation at ridges	333	(3)
What moves the plates?	336	(9)
Forces on plates	336	(2)
The hot-spot frame of reference: Plate velocities	338	(1)
Deducing the dominant drive forces	339	(1)
Plate tectonics and mantle convection	340	(1)
Summary	341	(2)
Further Reading	343	(1)
Problems	343	(2)
Is the Kenya Rift a New Plate Margin? A Regional Geophysical Study	345	(16)
Introduction: The East African Rift System	345	(2)
Morphology and geology of the Kenya Rift	347	(1)
Gravity studies	348	(1)
Seismic surveys	349	(7)
The seismicity of Kenya	349	(1)
Teleseismic studies	350	(1)
Seismic refraction and wide-angle reflection surveys	351	(5)
Combined seismic and gravity models	356	(1)
Heat flow studies	356	(3)
Electrical conductivity	359	(1)
Summary	360	(1)
Further reading	360	(1)
Hydrocarbon Exploration	361	(17)
Introduction: Energy sources and the demand for hydrocarbons	361	(3)
The origin and accumulation of hydrocarbons	364	(1)
Where sedimentary basins form	364	(2)
Exploration for petroleum	366	(1)
The West Sole gas field of the southern North Sea: A case study	367	(3)
The Forties oil field of the northern North Sea: A case study	370	(6)
Discovery and initial development of the field	370	(3)
Further development of the Forties field	373	(3)
The future	376	(2)
Further reading	377	(1)
Exploration for Metalliferous Ores	378	(12)
Introduction: Metalliferous and other ore deposits	378	(1)
The formation of ores and their geophysical properties	378	(3)
Where ores form	381	(1)
Exploration for orebodies	382	(1)
The Elura Orebody, New South Wales, Australia: A case study	383	(7)
Background and reconnaissance surveys	383	(2)
Initial surveys of the Elura orebody	385	(1)
Evaluation of the deposit	386	(2)
Assessment of geophysical surveying methods	388	(1)
Further reading	388	(2)
Volcanoes	390	(9)
Introduction: Types of eruption and damage	390	(1)
Methods for investigating volcanoes and monitoring activity	391	(1)
The 1989--1990 eruption of Redoubt Volcano, Alaska: A case study	391	(3)
Background	392	(1)
The 1989--1990 eruption	392	(1)
Monitoring of activity	393	(1)
Etna lava eruptions 1991--1993: A case study	394	(5)
Background	394	(1)
Deformation and microgravity	394	(2)
The 1991--1993 eruption	396	(2)
Further reading	398	(1)
The Chicxulub Structure and the K/T Mass Extinction	399	(9)
Introduction	399	(1)
Impacts and craters	399	(2)
The Chicxulub structure	401	(5)
Background	401	(1)
The structure of Chicxulub	401	(3)
Ages of the Chicxulub structure and ejecta	404	(2)
The Manson Crater	406	(1)
Giant eruptions	406	(1)
Conclusions to date	406	(2)
Further reading	407	(1)
Hydrogeology and Contaminated Land	408	(12)
Introduction	408	(1)
Aquifers	408	(1)
Geophysical methods useful in hydrogeology	408	(1)
GPR surveying of the water table, the Netherlands: An example	409	(1)
Background	409	(1)
Offsets of the water table	409	(1)
Structural control of aquifers in East Anglia, England: A case study	410	(2)
Introduction	410	(1)
Geophysical surveys	410	(2)
Saline contamination of the Crag aquifer, East Anglia: A case study	412	(5)
Background	412	(1)
Geophysical surveys	413	(4)
Landfill sites and contaminated ground	417	(3)
Introduction	417	(1)
Investigation of a landfill in northern England: A case study	417	(1)
Landfill monitoring: A case study	418	(1)
Further reading	419	(1)
Location of Cavities and Voids	420	(9)
Introduction	420	(1)
Possible geophysical techniques for locating cavities	420	(3)
Seismic methods	420	(1)
Electrical methods	421	(1)
Magnetic methods	421	(1)
Gravity methods	422	(1)
Fracturing around cavities	423	(1)
Collapses in buried karstic terrain, Kuwait: A case study	423	(3)
Background	423	(1)
Gravity survey	424	(2)
Land reclamation, south Wales: A case study	426	(3)
Background	426	(1)
Gravity survey	427	(1)
Further reading	428	(1)
Archaeological Site Surveying	429	(10)
Site surveying	429	(1)
Archaeological features and their geophysical expression	430	(1)
Ditches, pits, and postholes	430	(1)
Foundations	430	(1)
Furnaces, fireplaces, and kilns	430	(1)
Geophysical methods useful for archaeological surveying	431	(3)
Magnetic and susceptibility surveys	431	(1)
Resistivity surveys	431	(1)
Ground-penetrating radar (GPR)	432	(1)
Other techniques	433	(1)
Display of data	433	(1)
A possible Roman villa: A case study	434	(1)
Background	434	(1)
Geophysical surveys	434	(1)
Hudson's Bay Company fur trade post: A case study	434	(5)
Background	434	(2)
Geophysical surveys	436	(2)
Further reading	438	(1)
Appendix A List of Symbols and Abbreviations	439	(3)
Appendix B Answers to Problems	442	(7)
Bibliography	449	(8)
Figure Sources	457	(4)
Index	461