UNIT 1
UNIT 2
UNIT 3
UNIT 4
SCIE 3001
1 - Nature of Living Things
1.4 Human Organ Systems and Health
4 - Cycles and Seasons
5 -Structure of the Earth, and Earth Movements
 

Unit 5: Structure of the Earth, and Earth Movements

5a Natural Disasters

How natural disasters (hurricanes, earthquakes, volcanoes, tornadoes) are caused

Earthquakes

  • Every year about 30,000 earthquakes are felt worldwide.
  • Only about 75 are considered major.
  • Most earthquakes occur in remote regions.
  • When the occasional earthquake occurs near a city it can cause serious damage.
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Earthquake in Chile 2010 Tsunami Damage  

Description

  • A vibration of the earth caused by the rapid release of energy.
  • Often cause when land slips along faults (cracks) in the earth crust.
  • Focus – This is the point where the earthquake starts.
    • Energy radiates in all directions from the focus.
    • The seismic waves radiate throughout the earth.
  • Epicenter – This is the point on the earth’s surface directly above the focus.
  • Faults – Fractures in the earth’s crust where movement has occurred.

 

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 Focus, and Epicenter of an Earthquake

Causes

  • Before the great 1906 San Francisco earthquake, the cause and effects of earthquakes were not understood.

Observations from the 1906 earthquake

  • The San Andreas fault is a 1300 km fracture running north to south in California.
  • Earth’s surface shifted by several metres horizontally along the northern portion of the San Andreas Fault.
  • Land on the western side of the fault moved as much as 4.7m to the north compared to the land on the eastern side of the fault.
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San Andreas Fault
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Hypothesis - Elastic Rebound Hypothesis

  • A – Original position of existing fault.
  • B. Strain builds up as earth movements (kinetic energy) creates forces within the Earth’s crust deforms the rocks. The rocks store this kinetic energy as Potential Energy.
  • C – Suddenly the friction preventing movement is overcome and the rock slips at its weakest point (the focus).
  • D -This causes new forces on other parts of the fault, and additional slippage may occur until most of the potential energy is released as seismic waves. The vibrations (seismic waves) released is called the earthquake as the deformed rocks snap back in place.

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Aftershocks and Foreshocks

  • When an earthquake occurs, most of the movement happens in a short space of time.
  • Generally additional movement occurs along the fault and nearby faults for several days.
  • Aftershocks are these smaller earthquakes the occur after the main quake.
  • Foreshocks are those smaller quakes which occur before the main quake.
  • In some cases foreshocks may occur days or even years before the main quake.
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Aftershocks for a earthquake near Peru in 2001

Measuring Earthquakes

  • First attempt was made about 2000 years ago by the Chinese. Instrument to record and measure earthquakes is called a Seismograph. Seismographs work on the principle of inertia.
  • Instrument to record and measure earthquakes is called a Seismograph.
  • Seismographs work on the principle of inertia.
  • Movement of the earth is recorded on a rotating drum called a seismogram.
  • Different kinds of waves are recorded by the seismogram.
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Ancient Chinese Seismograph
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Seismogram
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Earthquake Waves

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Earthquake Damage

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Side to side movement produced by surface waves can cause damage to the foundations of building.
Rolling movement produced by surface waves can cause damage to the infrastructure and buildings.
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The back and forth movement produced by P waves can cause the ground to buckle and fracture
S waves can cause the ground to shake up and down and side to side.

Earthquake Zones

  • About 95% of earthquakes occur in a few narrow zones.
  • Most of these occur around the outer edge of t he Pacific Ocean.
  • Other Zones – The Mediterranean, Mid Atlantic Ocean and Indian Ocean.
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Intensity or Magnitude

  • Intensity is a qualitative measure of the amount of damage to estimate the amount of shaking. – Richter Scale or Modified Mercalli Scale.
  • Magnitude is a quantitative measure that measure the amount of energy released or the size of the seismic waves. – Moment Magnitude.
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Seismic Vibrations

Observation

  • Some buildings undergo little damage, while nearby buildings are almost destroyed.
  • Damage to infrastructe depends on several factors:
    • Intensity and duration of vibrations.
    • Nature of building materials.
    • Building design.
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Building Collapse
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Earthquake in China's south-western province of Sichuan

Building Design

  • Observation In the 1964 Alaska earthquake all multi-storey buildings were damages but wooden frame homes were less damaged
  • Hypothesis Flexible frames withstand vibrations better than rigid structures.
  • Unreinforced stone or brick buildings are most susceptible to damage.
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1964 Alaska earthquake damage
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1964 Alaska earthquake damage: Steel frame building largely unaffected but unreinforced brick building in the background severely damaged.
   
   
   

 

Hurricanes

  • Also known as tropical cyclones and typhoons.
  • Hurricanes are huge storms.
  • They can be up to 600 miles across and have strong winds spiralling inward and upward at speeds of 75 to 200 mph.
  • May last for over a week, moving 10-20 miles per hour over the open ocean.
  • Its centre is called the eye with warm air light winds and fair weather.
  • The low level storm winds blow counter clockwise around the eye in the Northern Hemisphere and clockwise in the Southern Hemisphere.
  • High up, winds spiral outwards and clockwise in the Northern Hemisphere.
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RETROGRADE
 
RETROGRADE

Tornadoes

  • Tornadoes are nature’s most violent storms spawned from powerful thunderstorms.
  • A tornado appears as a rotating, funnel-shaped cloud that extends from a thunderstorm to the ground with whirling winds that can reach 300 miles per hour.
  • Spawned from powerful thunderstorms, tornadoes can cause fatalities and devastate a neighborhood in seconds.
  • Damage paths can be in excess of one mile wide and 50 miles long.
  • Air heats up and hot air rises As the air rises it begins to rotate.
  • The moisture in the air condenses.
  • Thunder clouds form.
  • The violent movement of air upwards creates a vortex of rotating winds.
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Tornado After tornado Waterspout (tornado over water)
 
 

5b.Formation of soils

Weathering is the process of the breaking down rocks.

  • There are two different types of weathering
    • Physical weathering breaks down the rocks, but what it's chemical nature stays the same.
    • Chemical weathering - rocks still break down the, but it may change the chemical nature and hence the physical nature. For example, a hard material may change to a soft material after chemical weathering.
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Stage 1

  • The formation of soil happens over a very long period of time.
  • It can take 1000 years or more.
  • Soil is formed from the weathering of rocks and minerals.
  • The surface rocks break down into smaller pieces through a process of weathering and is then mixed organic matter.
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Stage 2

  • Over time this creates a thin layer of soil.
  • Plants and animals help the development of the soil.
  • When they die and decay they add organic matter to the soil (humus).
  • Humus helps hold water and provides nutrients for plants.

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Stage 3

Soil Composition - Soils are a mixture of different things:

  • rocks
  • minerals,
  • dead, decaying plants and animals
  • water
  • air.
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Soil has particles of different sizes.

Component

Size

Sand

Large (2.0 -0.02 mm)

Silt

Small (0.02 -0.002 mm)

Clay

Smaller (>0.002 mm)

 

Soil Texture and Properties

Texture

Water Infiltration

Water-holding Capacity

Nutrient-holding Capacity

Aeration

Sand

Good

Poor

Poor

Good

Silt

Medium

Medium

Medium

Medium

Clay

Poor

Good

Good

Poor

Loam

Medium

Medium

Medium

Medium

Productive Soil

  • Good supply of nutrients and nutrient-holding capacity
  • Infiltration, good water-holding capacity, resists evaporative water loss
  • Porous structure for aeration
  • Near-neutral pH
  • Low salt content

What is Loam?

  • Loam is soil composed of sand and silt, and a smaller amount of clay.
  • The concentrations can vary to give different kinds of loam.
 
   
Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.