Introduction to Geophysics Lecture Notes PDF

# Introduction to Geophysics ## Basics of Geophysical methods **Dr. Manal M. Osman** Lecture of Geophysics Alexandria University, Egypt. [email protected] ## Lecture 1 - Coarse Materials - Geophysics - Types of rocks - Physical properties of rocks - Geophysical methods classification #...

# Introduction to Geophysics ## Basics of Geophysical methods **Dr. Manal M. Osman** Lecture of Geophysics Alexandria University, Egypt. [email protected] ## Lecture 1 - Coarse Materials - Geophysics - Types of rocks - Physical properties of rocks - Geophysical methods classification ## Introduction to Geophysics The image shows a diagram illustrating the various methods used by geophysicists. The methods include: - **Well Calibration** - **Al Inversion** - **Porosity Modeling** - **Fluid prediction** - **Seismic Stratigraphy** - **Seismic Interpretation** - **AVO & Attribute Calibration** - **Al & El Inversion** The methods are arranged like concentric rings around the words "Geophysics." ## Coarse Materials The image shows book covers related to geophysics: - **Fundamentals of Geophysics, Second Edition** by William Lowrie - **Field Geophysics, Third Edition** by John Milsom - **An Introduction to Geophysical Exploration** by Philip Kearey, Michael Brooks and Ian Hill - **Physical Properties of Rocks, a Workbook** by J.H. Schön The image also includes logos from: - **Yukon College** - **Suez Canal University** ## Geophysics The image shows a cartoon with four stick figures. - the first holds its head with its hands and has a large question mark above it. - the second looks like it is working on a large gear. - the third has a lightbulb with a light on above its head. - the fourth holds its thumb up with an exclamation mark above it. There is a firework in the background. ## 1- Geophysics Geophysics is the application of the method of physics to the study of the Earth. The rocks do not differ only by their macroscopic or microscopic properties. As the rocks differ according to their origin, structure, texture, etc. they also differ by their density, magnetization, resistivity, etc. Geophysics developed from the disciplines of physics and geology and has no sharp boundaries that distinguish it from either. The use of physics to study the interior of the Earth, from land surface to the inner core is known as solid earth Geophysics Solid Earth Geophysics can be subdivided into Global Geophysics or pure Geophysics and Applied Geophysics. ### Applied Geophysics - Determination of the thickness of the crust (which is important in hydrocarbon exploration). - Study of shallow structures for engineering site investigations. - Exploration for groundwater and for minerals and other economic resources. - Trying to locate narrow mine shafts or other forms of buried cavities. - The mapping of archaeological remains. ### Definitions 1. **Applied geophysics** Making and interpreting measurements of physical properties of the Earth to determine sub-surface conditions, usually with an economic objective (fuel or mineral). 2. **Engineering geophysics** The application of geophysical methods to the investigation of sub-surface materials and structures that are likely to have (significant) engineering implications. 3. **Environmental geophysics** The application of geophysical methods to the investigation of nearsurface bio-physico-chemical phenomena that are likely to have (significant) implications for the management of the local environment. 4. **Hydro-geophysics** Geophysics in groundwater investigations. The problem is that the physical properties do not always clearly correlates with geological classifications and do not necessarily easily translates into the geological terms. ### What does this mean? Let's take the density as an example. - A rock sample and we have measured the value of density to be 2.60 g/cm3. According to this value we could assume that the rock sample could be, e. g. a limestone, some shale, compact sandstone, rhyolite, phonolite, andesite, granite, possibly some kind of schist and many others. - The wide range of possible rock types suggests that the physical properties does not directly refer to the geological classification. The image shows a diagram with a vertical axis labeled *Density, g/cm3* and a horizontal axis ranging from 1.6 to 3.0. It shows the density of various rocks, including: - Igneous rocks - Limestone - Shale - Sandstone - Soil and alluvium - Salt ## 2- Types of Minerals Minerals are classified based on their chemical composition: - **Native elements:** - Gold (Au) - Silver (Ag) - Sulfur (S) - **Sulfides:** - Pyrite (FeS) - Galena (PbS) - **Oxides:** - Hematite (Fe2O3) - Sapphire (Al2O3) - **Silicates:** - Quartz (SiO2) - Mica (KAl2(AlSi3O10)(OH,F,Cl)2) - Feldspar (KAlSi3O8) The image shows a diagram illustrating various characteristics of a mineral: - **Naturally occurring** - **Inorganic** - **Solid** ## 2- Types of Rocks ### Igneous Rocks The image shows various igneous rocks: - **Granite** - **Diorite** - **Gabbro** - **Peridotite** - **Rhyolite** - **Andesite** - **Basalt** - **Komatiite** The image also shows a diagram illustrating the mineral composition of various igneous rocks. The diagram has a vertical axis labeled Mineral Composition (%) and a horizontal axis labeled SiO2 (%). The diagram shows the composition of various rocks, including: - **Felsic** - Potassium Feldspar - Quartz - Plagioclase Feldspar - Na-rich - Biotite - Amphibole - **Intermediate** - **Mafic** - Ca-rich - Olivine - Pyroxene - **Ultramafic** ### Sedimentary Rocks The image shows a table showing the identification key for sedimentary rocks. The table is divided into two sections: *Detrital Sedimentary Rocks* and *Chemical Sedimentary Rocks.* The table includes columns for: - *Clastic Texture (particle size)* - *Distinctive Properties* - *Rock Name* - *Composition* - *Distinctive Properties* - *Rock Name* #### Detrital Sedimentary Rocks - **Gravel (Coarse)** - Rounded rock or mineral fragments, typically poorly sorted - Angular rock, or mineral fragments, typically poorly sorted - **Conglomerate** - **Breccia** - **Sand (Medium)**: - Quartz grains, typically rounded, well sorted - At least 25% feldspar, typically poorly sorted, angular fragments - Mixture of sand and mud, typically poorly sorted - **Quartz Sandstone** - **Arkose** - **Graywacke** - **Silt/mud (Fine)** - Mostly silt-size quartz and clay, blocky, gritty - Mostly clay, splits into layers, may contain fossils - Mostly clay; crumbles easily. - **Siltstone** - **Shale** - **Claystone** #### Chemical Sedimentary Rocks - **Crystalline Limestone** - Fine to coarse crystalline. - No visible grains, may exhibit conchoidal fracture - **Micrite** - Visible shells and shell fragments loosely cemented - **Coquina** - Various size shells and shell fragments, well cemented - **Fossiliferous Limestone** - Microscopic shells and clay, soft - **Chalk** - Faint layering, may contain cavities or pores - **Travertine** - Microcrystalline; may exhibit conchiodal fracture, will scratch glass - **Chert (light colored)** - **Flint (dark colored)** - **Agate (banded)** - **Rock Gypsum** - Fine to coarse crystalline, soft - **Rock Salt ** - Fine to coarse crystalline, tastes salty. - **Bituminous Coal** - Black brittle organic rock, may be layered ### Metamorphic Rocks The image shows a labeled diagram summarizing the identification of metamorphic rocks. The diagram includes a column for *texture*, another for *grain size*, and another for *composition*. The table includes various metamorphic rock types: - **FOLIATED** - **Slate** - **Phyllite** - **Schist** - **Gneiss** - **BAND-ING** - **Anthracite coal** - **NON-FOLIATED** - **Hornfels** - **Quartzite** - **Marble** - **Metaconglomerate** The image also shows a table summarizing the characteristics of each metamorphic rock type. **Key** - **MICa** - **QUARTZ** - **FELDSPAR** - **AMPHIBOLE** - **GARNET** - **PYROXENE** - **CARBON** **Type of Metamorphism** - **Regional** - **Contact** **Comments** - **Low-grade metamorphism of shale** - **Foliation surfaces shiny from microscopic mica crystals** - **Platy mica crystals visible from metamorphism of clay or feldspars** - **High-grade metamorphism; mineral types segregated into bands** - **Metamorphism of bituminous coal** - **Various rocks changed by heat from nearby magma/lava** - **Metamorphism of quartz sandstone** - **Metamorphism of limestone or dolostone** - **Pebbles may be distorted or stretched** ## 3- Physical properties of Rocks The image shows a diagram illustrating the physical properties of minerals. - **Streak** - **Luster** - **Color** - **Magnetism** - **Breakage** - **Hardness** ### Image 2 The image shows a table summarizing the physical properties of various rocks. The table includes columns for: - Rock - Dry Density(g/cm2) - Porosity (%) - Schmidt Hardness - Cerchar Abrasivity Index - P-Wave Velocity (m/s) - S-Wave Velocity (m/s) - Coefficient of Permeability (m/s) - Permeability (m2) - Bulk Density Pa (g/cm3) - Particle Density p (g/cm3) - Porosity (%) - N #### Igneous Rocks - Granite - Diorite - Gabbro - Rhyolite - Andesite - Basalt - Sedimentary - Condlomerate - Sandstone - Shale - Mudstone - Dolomite - Limestone #### Rock Unit - Mica schist - Biotite gneiss - Quartz-feldspar schist - Clorite-muscovite schist - Black schist - Serpentinite - Diopside skarn - Tremolite skarn - Diopside-tremolite skarn - Seprentine-tremolite rock - Serpentinite-talc rock - Serpentinite-tremolite - talc-carbonate rock - Serpentinite-tremolite carbonate - Serpentinite-clorite-tremolite rock - Quartz rock - Pegmatic granite - Dyke quartz The image shows the relationship between K (permeability) and p (density). The image shows a graph with an x-axis labeled *Density (g/cm3)* ranging from 2.5 to 3.0 and y-axis labeled *permeability (m2)* ranging from 10-20 to 10-8. ## 3- Physical Methods classification The physical properties of the rocks that are most commonly utilized in geophysical investigations are: - Density - Magnetic susceptibility - Elasticity - Electrical resistivity or conductivity - Radioactivity - Thermal conductivity These properties have been used to devise geophysical methods, which are: - Gravity method - Magnetic method - Seismic method - Electrical and electromagnetic methods - Radiometric method - Geothermal method ## Any Questions ## Thank You M.M.Osman