General Geology for Civil Engineering

• This module provides an overview of general geology for BS Civil Engineering students.
• Corresponds to IM No.: ENG GEO 2-2S-2023-2024

Chapter 1: General Geology

• Includes lesson titles on branches of geology, Earth's structure and composition, continental drift and tectonic plates, geological/Earth's processes, origin and occurrence of earthquakes, and the importance of geology to engineering.
• Upon completion, students should be able to identify geology branches, Earth's structure/composition/processes, compare continental drift and tectonic plates, and recognize the importance of geology to engineering.

Branches of Geology

• Geology is the study of the Earth; "geo" means "earth," and "logos" means "science."
• Branches include Physical, Mining, Petrology, Hydrology, Stratigraphy, Photo, Historical, Crystallography, Mineralogy, Paleontology, Structural, Engineering, Economic, and Geo Physics.
• Physical Geology focuses on earth's materials and energy.
• Mining Geology also focuses on earth's materials and energy.
• Petrology studies rock formation, structure, and composition.
• Hydrology focuses on earth's water and its movement.
• Stratigraphy examines rock layer order and geological time.
• Photo Geology uses aerial photos to study geological features.
• Historical Geology studies Earth's history.
• Crystallography studies crystal structure and properties.
• Mineralogy is the study of minerals.
• Paleontology studies fossilized plants and animals.
• Structural Geology focuses on rock arrangements and changes.
• Engineering Geology applies geological principles to engineering.
• Economic Geology studies profitable geological materials.
• Geo Physics studies Earth's physical properties and processes.

Earth's Structure and Its Composition

• The Earth consists of layers: crust, mantle, and core (outer and inner).
• The Earth's crust is the outermost layer with varied thickness and uneven surfaces that ranges from 5 to 25 miles (8 to 40 kilometers).
• Oceanic crust is thinner (4-7 miles), while continental crust is thicker (averaging about 19 miles).
• The mantle is below the crust, approximately 1,800 miles (2,900 kilometers) deep, primarily of solid rock containing silicate minerals.
• The outer core is below the mantle, 1,400 miles (2,250 kilometers) thick, mainly molten iron and nickel, creating Earth’s magnetic field via geodynamo.
• The inner core resides at Earth’s center, 800 miles (1,300 kilometers thick), mostly solid iron and nickel due to immense pressure.

Mechanical Earth's Structure

• Lithosphere: solid outer part of Earth, including the crust and upper stiff mantle layer, extending to almost 100km depth.
• Asthenosphere: hotter, more liquid layer beneath the lithosphere, from 100km to 700km beneath the surface.
• Mesosphere: layer beneath the asthenosphere 410km to 660km below the surface, subjected to high pressures and temperatures.
• Outer Core
• Inner Core

Composition of Earth's Crust

• Major elements include Oxygen (46.6%), Silicon (27.7%), Aluminum (8.1%), Iron (5%), Calcium (3.6%), Sodium and Potassium (2.8%), Magnesium (2.1%), and Titanium (0.57%).
• Oxygen is found in silicates and oxides.
• Silicon is found in various silicate minerals.
• Aluminum is found in feldspar, bauxite, and various silicates.
• Iron is found in hematite and magnetite.
• Calcium is found in calcite and gypsum.
• Sodium and Potassium are found in feldspar.
• Magnesium is found in olivine and serpentine.
• Titanium is found in ilmenite and rutile.

Distribution of Elements

• Crust: silicate minerals, quartz, feldspar, mica, and various rocks.
• Mantle: silicate minerals, iron, magnesium, olivine, pyroxenes, and garnet.
• Outer Core: liquid iron and nickel.
• Inner Core: solid iron and nickel (due to intense pressure).

Continental Drift and Tectonic Plate

• Alfred Wegener's theory states that continental landmasses "drifted" across the Earth.
• Pangaea existed about 240 million years ago before breaking apart; Pannotia formed 600 million years ago, and Rodinia existed over a billion years ago.
• The Himalayan Mountain Ranges are still growing due to the Indian subcontinent pushing the Asian continent.
• Plate tectonics explains lithosphere movements, stating it's broken into interacting tectonic plates.
• Interactions cause earthquakes, volcanic eruptions, and mountain ranges.

Types of Plate Boundaries

• Divergent: plates move apart, magma rises, cools, and forms new crust.
• Convergent: plates move toward each other (oceanic-oceanic, oceanic-continental, continental-continental).
• Transform: plates slide past each other.

Earth's Processes/Geological Processes

Weathering: Breakdown of rocks

• Biological: caused by plants and animals' movement.
• Chemical: caused by chemicals in rainwater changing minerals in rock.
• Mechanical/Physical: physical processes affect the rock, like temperature changes or exposure to wind/rain/waves.

Erosion: movement of rock fragments

• Gravitational: rocks and sediments move due to gravity.

• Wind: wind carries sand and dust, wearing down surfaces.

• Rain: rain dislodges pebbles and soil; heavy rain washes sediments into streams/rivers.

• River and Stream: rivers deposit eroded materials downstream, eroding the outside bank more as they flow through flat areas.

• Decomposition: laying down sediment carried by wind, flowing water, sea, or ice.

  • Saltation: sand grains are picked up and moved by the wind.
  • Flowing Water: water moves particles of soil and rock.
  • Sea Waves: the sea carries material to create beaches and coastal features.
  • Glaciers: glaciers transport large sediments, leaving behind 'glacial erratic boulders.'

• Landforms: earth surface features that make up the terrain.

  • Major: mountains, hills, plateaus, plains.
  • Minor: buttes, canyons, valleys, basins.
  • Coastal: peninsulas, bays, lagoons.
  • Underwater: ocean basins, mid-ocean ridges.

• Categories of Landforms by Physical Attributes: elevation, orientation, slope, rock exposure, soil type.

• Relief: the variation in height across the land’s surface, influenced by underlying geology.

• Others: volcanism, tectonic activity, earthquakes.

Origin and Occurrence of Earthquakes

• Earthquake: sudden energy release beneath the Earth's surface that causes ground shaking.
• Fault/Fault Plane: the surface along which blocks of the Earth slip.
• Hypocenter: the point underground where the earthquake originates.
• Epicenter: the point on the Earth's surface directly above the hypocenter.
• Seismic Wave: energy radiating outward from the fault in all directions.
• Types of Seismic Waves: body waves (P-waves and S-waves) and surface waves (Love waves and Rayleigh waves).
  • P-Waves (Primary Waves): travel through the Earth causing expansion and compression, can move through solids, liquids, and gases.
  • S-Waves (Secondary Waves): shake the ground perpendicularly to travel direction, move only through solids.
  • Love Waves: move along the surface horizontally, shifting from side to side.
  • Rayleigh Waves: cause the ground to shake in an elliptical pattern, produce longer duration on seismic recordings.
• Foreshocks: smaller earthquakes before the mainshock.
• Mainshock: the largest main earthquake.
• Aftershock: smaller earthquakes after the mainshock.

Elastic Rebound Theory of Harry Fielding Reid (1911)

• Fracture of rocks results from elastic strains exceeding rock strength due to relative displacements in the Earth's crust.
• Relative displacements accumulate gradually over time, not suddenly.
• Only mass movements are the sudden elastic rebounds towards positions of no elastic strain.
• Earthquake vibrations originate from the fracture surface, starting from a small area that expands.
• Energy liberated during an earthquake was stored as elastic strain in the rock.

Types of Earthquakes

• Tectonic: caused by abrupt movement along faults and plate boundaries.
• Volcanic: caused by rising magma or lava beneath an active volcano.
• Magnitude: seismic measurements or scale of an earthquake.
• Intensity: measurement of the earthquake’s strength at specific locations.

Physical Clues for Earthquake Prediction

• Based on the Dilatancy Theory include monitoring physical parameters such as seismic P velocity, ground uplift, radon emission, electrical resistivity, and the number of seismic events.

PHIVOLCS Earthquake Intensity Scale (PEIS)

• Scale ranges from I (Scarcely Perceptible) to X (Completely Devastating).