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Geology · 400 Level
This is the complete lecture note for GEY 409 Applied Geophysics, prepared for Geology students at 400 Level. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: GEY 409 Course Title: Applied Geophysics Unit: 3 Unit List of series 1. Foundations of Geophysics 2. Seismic Exploration Techniques 3. Gravity and Electrical Methods 4. Geophysical Data Interpretation 5. Applied Geophysics with Software Tools 1.1 Historical Development and Scope of Geophysics - 1.1.1 Origins of Geophysics - 1.1.2 Branches of Geophysics - 1.1.3 Role of Geophysics in Earth Sciences 1.2 Physical Principles Underpinning Geophysics - 1.2.1 Newtonian Mechanics and Gravity - 1.2.2 Wave Propagation and Seismic Energy - 1.2.3 Electrical and Magnetic Properties of Earth Materials 1.3 Geophysical Investigation Techniques - 1.3.1 Field Survey Methods - 1.3.2 Data Acquisition Tools and Instruments - 1.3.3 Limitations and Challenges in Geophysical Investigations 1.4 Applications of Geophysics in Geological Problem-Solving - 1.4.1 Mineral and Hydrocarbon Exploration - 1.4.2 Engineering and Environmental Studies
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS - 1.4.3 Groundwater and Natural Hazard Assessment 1.5 Introduction to Geophysical Data Interpretation - 1.5.1 Basic Data Processing Concepts - 1.5.2 Qualitative and Quantitative Interpretation - 1.5.3 Importance of Accuracy and Reliability Introduction Geophysics provides us with a scientific lens through which we can investigate the hidden structures and processes of the Earth. From the exploration of natural resources to the assessment of environmental conditions, geophysics has become an indispensable tool in solving geological problems. This Series will introduce you to the essential foundations of geophysics, preparing you to appreciate its scope, principles, and applications as the basis for more advanced methods that follow in later Series. The aim of this Series is to equip you with a clear understanding of the historical development, physical principles, investigative techniques, and practical applications of geophysics, while also introducing you to the basics of geophysical data interpretation. We shall commence this Series by examining the historical development and scope of geophysics, highlighting its origins and role in Earth sciences. Next, we will explore the physical principles that underpin geophysical methods, including mechanics, wave propagation, and electrical properties. Following that, we will consider geophysical investigation techniques, focusing on field surveys, instruments, and challenges. Afterwards, we will move on to the applications of geophysics in solving geological problems such as exploration, engineering, and environmental studies. Finally, we will conclude with an introduction to geophysical data interpretation, emphasising the importance of accuracy and reliability in processing and analysing results. Series Learning Outcomes Upon completing this Series, you should be able to: - SLO 1.1 define the historical development and scope of geophysics, - SLO 1.2 explain the fundamental physical principles that underpin geophysical methods, - SLO 1.3 describe the main techniques used in geophysical investigations, including field surveys and instruments, - SLO 1.4 analyse the applications of geophysics in solving geological problems such as exploration, engineering, and environmental studies, and
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS - SLO 1.5 demonstrate the basic processes involved in geophysical data interpretation with emphasis on accuracy and reliability. 1.1 Historical Development and Scope of Geophysics 1.1.1 Origins of Geophysics Geophysics is the study of the Earth using the principles of physics, which is the branch of science concerned with nature and properties of matter and energy. The origins of geophysics can be traced back to early observations of natural phenomena such as earthquakes, magnetism, and gravity. Ancient civilizations noticed that lodestones could attract iron, and this curiosity eventually led to the study of geomagnetism, defined as the magnetic properties and behavior of the Earth. Similarly, the measurement of gravity and the study of seismic waves began as practical attempts to explain natural events and later evolved into scientific disciplines. Figure 1.1: Timeline of geophysics development Fill in the blank: The study of the Earth’s magnetic properties is known as ________. 1.1.2 Branches of Geophysics Over time, geophysics has developed into several specialized branches. These include seismology, which is the study of earthquakes and seismic waves; gravimetry, which involves measuring variations in the Earth’s gravitational field; and electrical geophysics, which examines how electrical currents and resistivity behave in subsurface materials. Each branch provides unique insights into the Earth’s structure and processes, and together they form a comprehensive toolkit for investigating geological problems. Branch Focus Area Seismology The study of earthquakes and the propagation of elastic seismic waves through the Earth to map its internal structure. Geodesy The science of accurately measuring the Earth's geometric shape, orientation in space, and gravitational field.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Branch Focus Area Geomagnetism The investigation of the Earth’s magnetic field, its origins in the core, and its variations over time. Gravimetry The measurement and analysis of variations in the Earth’s gravitational field to infer subsurface density contrasts. Geodynamics The study of the forces and physical processes that drive Earth’s internal motion, such as mantle convection and plate tectonics. Exploration Geophysics The application of physical methods (seismic, electrical, magnetic) to locate and evaluate natural resources like minerals, oil, gas, and groundwater. Environmental Geophysics The use of non-invasive geophysical techniques to solve environmental and engineering challenges, such as tracking pollutants or assessing construction sites. Marine Geophysics The application of geophysical principles to study the physical properties and structure of the ocean floor and marine environments. Box 1.1: Selected branches of geophysics - Seismology: study of seismic waves and earthquakes - Gravimetry: measurement of gravitational variations - Electrical geophysics: study of subsurface electrical properties - Magnetometry: measurement of magnetic fields - Geophysical exploration: application of methods to locate resources
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Fill in the blank: The branch of geophysics concerned with measuring variations in the Earth’s gravitational field is called ________. 1.1.3 Role of Geophysics in Earth Sciences Geophysics plays a central role in Earth sciences by providing tools to probe beneath the surface without direct excavation. It helps geologists map subsurface structures, identify mineral deposits, assess groundwater resources, and evaluate environmental hazards. For example, seismic surveys are used in hydrocarbon exploration, while electrical resistivity methods are applied in groundwater studies. The scope of geophysics extends beyond resource exploration, contributing to engineering projects, environmental monitoring, and disaster risk reduction. Plate 1.1: Geophysicists conducting a seismic survey in the field Fill in the blank: Seismic surveys are commonly used in ______ exploration. Pilot Questions 1.1 1. Who were the earliest observers of natural phenomena that contributed to the origins of geophysics? 2. Define geomagnetism and explain its significance in the history of geophysics. 3. List three major branches of geophysics and briefly state their focus. 4. What is the role of geophysics in groundwater studies? 5. Why is geophysics considered a non-invasive tool in Earth sciences? 1.2 Physical Principles Underpinning Geophysics 1.2.1 Newtonian mechanics and gravity One of the most fundamental principles in geophysics is gravity, defined as the attractive force between two masses. The Earth’s gravitational field is not uniform, and variations in gravity provide clues about subsurface structures. These variations are explained by Newtonian mechanics, which is the branch of physics concerned with the motion of bodies under the influence of forces. In geophysics, gravity surveys are used to detect density contrasts in rocks, which may indicate the presence of mineral deposits or voids. Figure 1.2: Gravity anomalies caused by subsurface density contrasts
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Fill in the blank: Variations in the Earth’s gravitational field are often linked to differences in ________ of subsurface materials. 1.2.2 Wave propagation and seismic energy Another key principle is wave propagation, defined as the movement of energy through a medium in the form of waves. In geophysics, seismic waves generated by natural earthquakes or artificial sources travel through the Earth and are recorded by instruments. The speed and behavior of these waves depend on the properties of the rocks they pass through. By studying seismic energy, geophysicists can infer the structure and composition of the subsurface. Plate 1.2: Seismic wave propagation through Earth’s layers Fill in the blank: The movement of energy through a medium in the form of waves is called ______. 1.2.3 Electrical and magnetic properties of Earth materials The subsurface also exhibits distinctive electrical properties, defined as the ability of materials to conduct or resist electrical current, and magnetic properties, defined as the ability of materials to respond to magnetic fields. These properties vary depending on the type of rock, its moisture content, and mineral composition. Electrical methods such as resistivity surveys are used to locate groundwater or detect contamination, while magnetic surveys help identify ore bodies and geological structures. Property Definition Geophysical Application Electrical Resistivity ($\rho$) A measure of how strongly a material opposes the flow of electric current. Measured in $\Omega \cdot m$. Detecting fluid-filled fractures, clay content, and groundwater salinity. Electrical Conductivity ($\sigma$) The inverse of resistivity ($\sigma = 1/\rho$). Measured in Siemens/meter ($S/m$). Identifying conductive ore bodies (sulfides) or saline plumes.
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