ERTH 375 Final - UofC

CHAPTER 1:

Relationship between Natural Disaster Fatalities and Population Density

Proportional (more people = more deaths)

Economic Damage from Natural Disasters (3)

• Loss of Productivity

• Infrastructure

• Wages

Magnitude and Frequency

Larger disaster = less frequent, smaller disaster = more frequent

Demographic Transition Model (3)

• Before Transition

• During Transition

• After Transition

Before Transition:

High birth, high death

During Transition:

High birth, low death

After Transition:

Low birth, low death

Carrying Capacity

Number of people that can survive given limited resources

Potato Blight in Ireland

• 1500s: potatoes increased = population increased = carrying capacity increased

• 1840s: potatoes blight (shortage) = population decreased = carrying capacity decreased

Return Period (2)

• Smaller disasters = shorter, bigger disasters = longer

• 10-fatality > 100-fatality > 1000-fatality

Population Growth vs Natural Disasters (2)

• Increased population leads to higher costs and greater impacts from disasters

• Concentrated in developing countries

Human Population Increases by _________ people annually

~80 million

CHAPTER 2:

Origin of Planets

• Gas, ice, dust, and debris accrete under gravity

Origin of the Sun (2)

• From the accumulation and accretion of matter in a rotating disk

• Nuclear Fission: H → He + heat

• Central temp increases >10⁶

Gravity Organizes Material in the Solar System

Forms rings → planetesimals → planets

Why are planets close to the Sun rocky?

Solar heat scrubs gases and liquids away

Scientific Criteria for Defining a Planet (3)

• Elliptical orbit

• Spherical Shape

• No other planet/planetesimals in orbit

How old is Earth?

4.57 billion years old

Oldest Earth Materials (2)

• Zircon crystals (Australia)

• 4.4 billion years old

Earth’s Internal Heat Generation (3)

• Impact energy

• Gravitational (frictional) energy

• Radioactive decay

Layers of Earth (4)

• Inner core (solid)

• Outer core (liquid)

• Mantle (stony)

• Crust (low-density rock; melt)

Frictional Heat from _____ forced towards Earth’s core due to gravity

Fe

Earth’s Magnetic Field

Viscous convection currents in the core

Density in Earth’s Layers

Increasing density from inner core and outwards

Layers of Earth Strength-Wise

Lithosphere (solid) > asthenosphere (‘plastic rock’) > mesosphere (‘stiff plastic’)

Material Behavior (3)

• Elastic: Returns to original shape

• Ductile: Bends or deforms under stress over time or high temperature

• Brittle: Breaks or shatters

Material Behavior of Earth’s Surface

Elastic and brittle

Material Behavior of Asthenosphere

Ductile (soft plastic)

Material Behavior of Mesosphere (deep mantle)

Ductile (stiff plastic)

Role of Asthenosphere in Earth’s Shape

Facilitates Earth’s oblate spheroid shape and daylights at mid-ocean ridges

Isostasy

The Earth's crust “floats” on the mantle

Isostatic Subsidence

Crust sinks under added weight (e.g., glaciers)

Isostatic Rebound

Crust rises when weight is removed (e.g., glacier melt)

Total Internal Heat Drives (3)

• Plate tectonics 

• Earthquakes

• Volcanic eruptions

Oldest Rocks on Earth

4.055 billion years old (NW Canada)

Development Plate Tectonics Concept

Theory of plate tectonics developed by scientists and widely accepted in the 1960s

Three types of Plate Boundaries (3)

• Divergent

• Transform

• Convergent

Divergent Plates

Plates pull apart

Transform Plates

Plates slide past each other

Convergent Plates

Plates collide

Tectonic Cycle (4 steps)

1. New crust forms (divergence)

• Magma from inside Earth comes up through cracks (divergent boundaries) where two plates move apart 

• Cools down and forms new oceanic crust (usually under ocean)

2. Plates move apart

• As more crust is made, oceanic crust spreads apart making room for more

• Older, colder, and denser crust oceanic will get subducted (forced down) beneath younger, lighter crust

3. Plates collide (convergence)

• In some places, plates move towards each other (convergent boundaries)

• One plate, usually heavier and older one, gets pushed underneath the other 

4. Old crust recycled 

• As old crust is subducted, it’s eventually melted and reabsorbed into the mantle 

• The cycle takes about 250 million years

What is stored in volcanic and sedimentary rocks?

Magnetic polarity

• Shows Earth’s magnetic field reversals

Epicenter

Point on the surface above the earthquake origin

Hypocenter

Actual origin point under the surface

Shallow and Deep Earthquakes (2)

• Shallow: divergent boundaries

• Deep: convergent boundaries

Oldest Ocean Floor Rocks

200 million years old

Ocean Basins (2)

• Constantly created at mid-ocean ridges

• Destroyed at subduction zones

Hot Spots (2)

• Mantle areas where hot material rises, forming volcanoes

• Further away from hotspot = oldest volcanoes

Seafloor Depth (2)

• Seafloor depth increases as we move away from mid-ocean ridges

• Oceanic crust ages = cools, becomes denser, sinks deeper into mantle

Pangea and Panthalassa (3)

• Pangea: Supercontinent (~40% of Earth’s surface)

• Panthalassa: Surrounding superocean (~60% of Earth’s surface)

• 220 million years ago

Pangea Breaks Down Into ________________

 Laurasia & Gondwanaland, 180 million years ago

North Atlantic Ocean opened

 India moved towards Asia, 135 million years ago

Uniformitarianism

Physical laws today apply directly to events of the past

CHAPTER 3:

Fault Release (2)

• Fault: A fracture in Earth’s crust

• Stress: Strain causing deformation across a fault.

Strain Propagation

Strain propagates as seismic waves, including Love and Rayleigh waves

Laws of Geologic Mapping (3)

• Law of Horizontality

• Law of Superposition

• Law of Original Continuity

Law of Horizontality

Sediments accumulate in horizontal layers

Law of Superposition

Oldest layers are at the bottom, newer layers are on top

Law of Original Continuity

Sediment layers are continuous horizontally unless interrupted

Types of Faults (4)

• Joints

• Offset

• Strike

• Dip

Joints

Fractures and cracks in brittle lithosphere rocks

Offset

Displacement or shift of rock layers or faults

Strike

Direction of a rock layer across the landscape

Dip

Angle at which the rock tilts from horizontal

Dip-Slips Faults (3)

• Dominated by vertical offset

• Footwall: bottom side fault

• Hanging Wall: top side fault

Dip-Slips Faults: Normal

Hanging wall moves down (divergent)

Dip-Slips Faults: Reverse

Hanging wall moves up (convergent)

Strike-Slip Faults (2)

Right Lateral: Right side moves towards the observer.

Left Lateral: Left side moves towards the observer.

Fault Ruptures

Events over time where faults release energy as seismic waves, leading to earthquakes

Tools to Measure Seismic Activity (2)

• Seismometers: Detect seismic waves

• Seismographs: Record seismic waves

Body Waves (2)

•  P waves & S waves

• Fast and high-frequency, travel through interior

Surface Waves (2)

• Rayleigh & Love waves

• Slower and low-frequency, travel along surface

P (primary) Waves (3)

• Fastest

• Supported by all phases of matter 

• Varies with compressibility, shear strength, density of matter

S (secondary) Waves (4)

• Follows primary to detector

• Shear strain along the propagation

• Supported by solid matter

• Varies with shear strength & density of matter

Speed of Waves in Earth (2)

• Waves increase in speed with depth

• Slows in asthenosphere (weak shear) → increases in mantle until core boundary → outer core: p waves slow, s waves disappear (no shears) → p waves increase through outer core and inner core

Love Waves (2)

• Move ground side to side

• Faster than Rayleigh waves, but slower than S and P waves

Rayleigh Waves (4)

• Backward rotating (retrograde), elliptical motion

• Vertical and horizontal shaking

• Travel furthest, slowest

•  More energy is released when earthquake hypocenter is close to surface

Seismic Moment (M₀)

• Strain energy released

  M0 = shear strength × rupture area × displacement

Phases of Earthquakes (3)

• Foreshock

• Mainshock

• Aftershock

Foreshock

Small events before the mainshock

Mainshock

Largest event

Aftershock

Smaller events following the mainshock

How does fault-rupture length relate to earthquake magnitude?

Longer rupture length = higher magnitude

• (e.g.) 100m long rupture = magnitude 4 → 1000km = magnitude 9

High-Frequency Waves: Damage

More damage near epicenter

Low-Frequency Waves: Damage

Travels further and causes widespread damage

Ground Motion (2)

• Horizontal Shaking: massive damage to buildings

• Measured in acceleration

Building Response to Earthquakes (3)

• Natural frequency

• Material flexibility

• Resonance matching wave periods

Building Responses: Seismic Velocity through Materials (5)

• Flexible materials (wood, steel) → longer period of shaking

• Stiff materials (brick, concrete) → shorter period of shaking

• Faster through hard rocks, slower through soft rocks

• Increase amplitude when traveling through softer rock to carry high-energy

• If period of wave matches period of building → shaking amplified → resonance results

Mercalli Intensity Scale (2)

• I to XII scale

• Assesses earthquake effects on people and buildings

CHAPTER 4:

Divergent Plate Boundary (Spreading Centers)

A boundary where plates move apart, rocks fall easily in tension, and small earthquakes occur (e.g., in Iceland)

Transform Plate Boundaries

Plates slide horizontally past each other, and stress builds up at irregularities, causing earthquakes when released

Convergent Boundaries

Plates collide → require a large amount of energy → largest earthquakes

Red Sea and Gulf of Aden (2)

• A young spreading center where an ocean basin is forming, with three rifts meeting at a triple junction

• Arabian plate diverging from African plate, Somali plate potentially diverging from African plate

Subduction Zones

Regions where oceanic plates are subducted (forced downwards), generating great earthquakes

Why do deep earthquakes lose energy before reaching the surface?

Energy dissipates due to the depth of subduction (up to 700 km)

Seismic Gap Method (3)

• Used to predict future Earthquakes by analyzing fault segments

• Recent failed segments = low probability of Earthquake

• Recently non-failed segments = high probability of Earthquake