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Natural Disasters

Course Information – Welcome!
Video lectures and course content were created by Mareike Adams

Course Instructor:

Samuel Morton (samuel.morton@carleton.ca)

Office hours: Thursdays 10:00 – 11:00, in HP 2125

Teaching Assistants:

Naomi Weinberg (naomi.weinberg@carleton.ca)

Office hours: Mondays 2:00-3:00 PM in HP2125

Nabil Shawwa (nabil.shawwa@carleton.ca)

Office hours: Tuesdays 1:00-2:00 PM in HP2125

Yingzhou Li (yingzhou.li@carleton.ca)

Office hours: Wednesdays 1:00-2:00 PM in HP2125

Please visit or email us if you have any questions/concerns!

mailto:mareikeadams@umail.ucsb.edu

mailto:naomi.weinberg@carleton.ca

mailto:nabil.shawwa@carleton.ca

mailto:naomi.weinberg@carleton.ca

Lectures & CUOL
CUOL Web Channel

The CUOL Web Channel will play a recorded video of the lecture on their web

channel:

https://vod.cuol.ca/stream/web-channel

Initial Show Time: Mondays at 1:00 PM – 3:45 PM EST

Repeat Show Time: Tuesdays at 1:30 AM – 4:15 AM EST

Video on Demand (VOD)

For a $50 subscription fee, you can access the recorded videos of the lectures

at any time. You can also rent individual lectures for $6 each.

https://vod.cuol.ca/vod

CUOL Student Centre (Loeb D299)

The CUOL Student Centre has kiosks available to view each lecture for free,

available 24 hours a day, 7 days a week.

Lectures can also be freely viewed on campus using computer terminals, such

as those found at the MacOdrum Library.

https://vod.cuol.ca/stream/web-channel

https://vod.cuol.ca/vod

CUOL Information and Assistance

CUOL website: www.carleton.ca/cuol

Video On Demand login page: https://vod.cuol.ca/vod

CUOL Student Centre: D299 Loeb, 613-520-4055

General Information:

Email: cuol@carleton.ca

Video on Demand support and questions:

Email: vod@carleton.ca

http://www.carleton.ca/cuol

https://vod.cuol.ca/vod

mailto:cuol@carleton.ca

mailto:vod@carleton.ca

Course Information

Optional Texts:

Natural Hazards, 4th or 5th Edition, Edward A. Keller & Duane E. Devecchio

OR

Natural Disasters – Canadian Edition, 4th edition, Abbott, P.L. and Samson, C. 2015

Grading:

Quizzes:

• 4 quizzes – 5% each – multiple choice

• Each will take ~30 min to 1 hr. You will have 3 hours.

• Open on CuLearn for 4 days – but you only have 1 chance to complete it

• Once you have started the quiz it will be open for the allotted time – closing the
browser will not stop the clock!

Quizzes: 20%

Midterm Exam: 40%

Final Exam: 40%

Course Information

Quiz breakdown:

Quiz 1 : Lectures 1-3

Quiz 2 : Lectures 4-5

Quiz 3 : Lectures 6-7

Quiz 4 : Lectures 8-1

0

Quizzes:

• After you finish a quiz, you can immediately see how you scored – but
not the questions you missed

• Open book – but you cannot do them in groups!

• Should you experience problems during your Quiz:
• Note the

time

• Take a screenshot of the problem

• No accommodation will be made to waive or redo a Quiz unless supporting or
substantiating documentation is provided

Course Information
Grading:

Exams:

• Midterm Exam will occur on February 29th from 2:30 – 4:30 pm

• Lectures 1-5

• Final Exam will occur during final exam period (Date/Time To Be Announced)

• Lectures 6-11

• Local students, living within 100km of Carleton, write their exams on campus.

• Distance students, living over 100km from campus, will write exams at either

a Carleton University Test Centre or may apply to write the exam at distance

with a proctor. Distance students should apply through CUOL immediately.

Quizzes: 20%

Exam 1: 40%

Exam 2: 40%

NO

questions/emails

regarding exams will

be answered on the

day of the actual exam

Course Timeline for Winter 2020

Offshore British Columbia–Southeastern Alaska

2017 Mw 7.1 earthquake, central Mexico

Hurricane Harvey – Category 4

Credit: NASA/NOAA GOES Project
Hurricane Irma – Category 4

Hurricane Maria – Category 4

2017 Hurricane Patterns

Hurricane Harvey – Category 4
Credit: NASA/NOAA GOES Project
Hurricane Irma – Category 4
Hurricane Maria – Category 4

Is this normal??

Hurricane Sandy (2012)

Map by Robert Simmon, using

data from the NOAA Earth System

Research Laboratory

Course Objectives

• Demonstrate a comprehension of Earth’s geologic, hydrologic
and atmospheric processes

• Identify the cause and effect relationships between earth
processes and natural hazards

• Assess the associated risks of natural disasters on human
societies and identify when a hazard becomes a catastrophe

• Discuss if and how geological catastrophes can be predicted,
mitigated, and avoided

• Develop and apply skills in scientific observation, data
interpretation and critical thinking

Why Studying Natural Hazards is Important

• Have experienced large, costly, and deadly natural hazards

since 1995

• Deadliest tsunami caused by earthquake in Indian Ocean

• Tsunami in Japan caused by largest and costliest earthquake in

recorded history

• Catastrophic flooding in different areas of the world

• Volcanic eruptions that shut down international airports

• Worst tornado outbreak in U.S. history

• Etc.

Forgan,

Oklahoma

Processes: Internal and External

• Processes
• Physical, chemical, and biological ways in which events

affect Earth’s surface

• Internal processes come from forces within Earth
• Plate tectonics

• Result of internal energy of Earth

• External processes come from forces on Earth’s
surface
• Atmospheric effects

• Energy from the Sun

Hazard, Disaster, or Catastrophe

• Hazard
– Natural process or event that is a potential threat to human

life or property

• Disaster
– Hazardous event that occurs over a limited time in a

defined area
– Criteria:

1) Ten or more people killed
2) 100 or more people affected
3) State of emergency is declared
4) International assistance is requested

• Catastrophe
– Massive disaster that requires significant amount of money

or time to recover

Natural Disaster ?

A large earthquake occurs:

– In Vancouver:

– On an Arctic Island:

YES

NO

Natural Disaster ?
A large earthquake occurs:

– In Vancouver: YES

– On an Arctic Island: NO

Misnomer

– Gives the impression that disasters are only the

fault of nature

– “Natural” disasters often triggered when society

ignores natural hazards

Natural Hazard?

A large earthquake occurs:
– In Vancouver:
– On an Arctic Island:

A source of danger that exists in the environment

and that has the potential to cause harm.

– Potentially damaging

– Ex. unstable snow on a mountain slope, high water

levels, etc.

YES
YES

Some Major Hazards in Canada

Major Hazards in the United States

Hazard, Disaster, or Catastrophe, cont.

• During past half century, there has been a dramatic

increase in natural disasters :

– Examples: Haitian earthquake, Indonesian tsunami,

Hurricane Katrina

• United Nation: 1990’s “International Decade for

Natural Hazards Reduction”

– Mitigation

• Reduce the effects of something

• Natural disaster preparation

Numbers, Effects, and Causes of Worldwide

Natural Disasters

Numbers, Effects, and Causes of Worldwide
Natural Disasters

• Storms attain category 3 wind speeds

~9 hrs faster than in 1980s

• Global wind speeds have increased

by ~5% over last 20 yrs

• In ground-based records, ~76% of

weather stations in the USA have

seen increases in extreme

precipitation since 1948

• Rainfall totals from tropical cyclones

in North Atlantic have risen at a rate

of 24%/decade since 1988

• Twice as many extreme regional

snowstorms between 1961-2010 than

1900-1960 (William Lau, NASA’s

Goddard Space Flight Center)

• In 2005, Atlantic hurricanes are ~60%

more powerful than in the 1970’s

(Kerry Emanuel, MIT)

Numbers, Effects, and Causes of Worldwide
Natural Disasters

Asia is particularly vulnerable,

why?

Death and Damage caused

by Natural Hazards

• Effects of hazards can differ and change

with time because of changes of

patterns of human land use

• Natural hazards that cause the greatest

loss on human life may not cause the

most property damage

• Hazards vary greatly in their ability to

cause catastrophe

Prediction:

Where would you expect the greatest

damage/economic losses from

natural disasters?

A. Poorest nations

B. Developing nations

C. Industrial nations

World Disaster Damage ($)

0

100

200

300

400

500

Poorest nations Developing nations Industrial nations

Source: ICLR, based on data from International Red Cross

P. Kovacs, Institute for Catastrophic Loss Reduction, 2005

US$ billions (2000 prices),1991-2000

Prediction:

Where would you expect the greatest death toll from

natural disasters?
A. Poorest nations
B. Developing nations
C. Industrial nations

World Disaster Fatalities

0
100
200
300
400
Poorest nations Developing nations Industrial nations

Thousands of people, 1991-2000

Source: ICLR, based on data from International Red Cross
P. Kovacs, Institute for Catastrophic Loss Reduction, 2005

Earthquake in Haiti, 2010: A Human-Caused

Catastrophe?

• Earthquake became a
catastrophe
• Eighty-five percent of people in

Port-au-Prince lived in slum
conditions

• Poor conditions lead to 190,000
destroyed or damaged homes
• Killed a quarter million people

• Two million homeless with poor
sanitation and water quality

• Reason for catastrophe was
clear: heavy human footprint
• Large number of poorly

constructed buildings

• Population grew so fast

High death totals often related to economic and political factors

Earthquake in Haiti, 2010: A Human-Caused
Catastrophe?

Reason for catastrophe was clear: heavy human footprint
• Large number of poorly constructed buildings

• Population grew so fast

• 90% of mountainous regions have been deforested

• Dry, exposed land can easily emphasize massive floods + landslides

Natural Hazards and the Geologic Cycle

• Natural hazards are repetitive

• History of an area gives clues to potential hazards
– Maps, historical accounts, climate and weather data

– Rock types, faults, folds, soil composition

• Geologic conditions govern the type, location, and intensity of
natural processes

• Collectively, processes are called geologic cycle
– Subcycles:

• Tectonic cycle

• Rock cycle

• Hydrologic cycle

• Biogeochemical cycle

The Tectonic Cycle

• Refers to large-scale processes that deform Earth’s crust

and produce landforms

• Driven by forces within Earth (internal energy)

• Involves the creation, destruction, and movement of

tectonic plates

The Rock Cycle

• Rocks are aggregates of one or more minerals

• Recycling of earth materials linked to all other cycles

– Tectonic cycle: heat and energy

– Biogeochemical cycle: materials

– Hydrologic cycle: water for erosion and weathering

• Rocks classified according to how they were formed

in the rock cycle

The Rock Cycle, cont.

• Igneous rocks

– Form from crystallization of magma

• Sedimentary rocks

– Rocks are weathered into sediment by wind and water

– Deposited sediment undergoes lithification

• Metamorphic rocks

– Rocks are changed through extreme heat, pressure, or

chemically active fluids

The Rock Cycle

The

Hydrologic Cycle

• Movement of water between atmosphere and oceans

and continents driven by solar energy

• Processes include: evaporation, precipitation, surface

runoff, and subsurface flow

• Water is stored in compartments such as oceans,

atmosphere, rivers, groundwater, etc.

– Residence time is estimated average time that a drop of

water spends in any compartment

– Only a small amount of water is active at any given time

Hydrologic Cycle

Biogeochemical Cycle

• Transfer of chemical elements through a series of
reservoirs
– Atmosphere, lithosphere, hydrosphere, biosphere

• Related to the three previous cycles
– Tectonic cycle: water from volcanic processes; heat and energy

required

– Rock and hydrological cycles: involved in transfer and storing of
chemical elements

• Rates of transfer of important chemical elements are only
approximate
– Carbon, Nitrogen, Phosphorus

The World’s Water Supply (selected examples)

Fundamental Concepts for Understanding

Natural Processes as Hazards

1. Hazards are predictable from scientific evaluation

2. Risk analysis is an important component in our
understanding of the effects of hazardous processes

3. Linkages exist between different natural hazards
as well as between hazards and the physical
environment

4. Hazardous events that previously produced disasters
are now producing catastrophes

5. Consequences of hazards can be minimized

1. Hazards are predictable from scientific evaluation

• Location: Where might the event occur?

– Most hazardous areas are mapped

• Probability: How likely is it that the event will occur?

– Estimated based on past events and current conditions

• Precursor events: Could any recent events be a precursor for something else?

Forecast vs Prediction

• Prediction

– Specific date, time, and magnitude of event

• Forecast

– Range of probability for event

Most hazards can only be forecasted

2. Risk Analysis

Risk = (probability of event) x (

consequences

)

→Live in northern Saskatchewan?

→Live inside the crater of an active volcano?

→Live on the San Andreas fault?

Consequences: damages to people, property, economics, etc.

Acceptable Risk is the amount of risk that an individual or

society is willing to take

Problem: lack of reliable data for either the probability or

consequences

3. Linkages

Hazards may be linked to or cause one other

Hazards linked to earth materials

For example:

• Earthquakes can cause landslides

• Earthquakes and landslides can cause tsunamis

• Volcanic eruptions may be preceded by earthquakes

• Hurricanes can cause flooding

• Drought can make fires worse

• Global warming (climate change) could lead to more hurricanes

• Some rock types are prone to landslides

4. Disasters are now becoming Catastrophes

The world’s population is growing exponentially

• Grows by the addition of a constant percentage
of current population

• Has more than tripled in the past 70 years

The Problems:

• Increases number of people at risk

• Reduced availability of food & clean drinking water

• Greater need for energy and waste disposal

Examples:

Mexico City: 10,000 killed in 1985 8.0 earthquake

Izmit, Turkey: >17,000 killed in 1999 earthquakes

20th Century rapid rise in human population

Why does the

frequency

of natural disasters appear to

be increasing?

Has the frequency of natural hazards increased as well?

Great Natural Disasters 1950-2008

Number of Earthquakes M≥7.0 per Year

Number of Earthquakes M≥7.0 per Year

The number of earthquakes isn’t increasing

The population is!

Magnitude and Frequency of Hazardous Events

• Impact of hazards depend on:

– Magnitude: Amount of energy released (how large is the event)

– Frequency: Interval between occurrences

– Other factors: climate, geology, vegetation, population, and

land use

• Magnitude-frequency concept

– Frequency of an event inversely related to

magnitude

• Land use affects magnitude and frequency of events

Metrics to describe hazard levels: Frequency

• Number of similar events per unit time

• Example:

– On average, 4 former tropical cyclones affect

Atlantic Canada every year

– Frequency = 4 occurrences per year

Metrics to describe hazard levels:

Return Period

• Length of time between similar events

• Example:

– Severe hurricanes strike the US on average every

6 years

– This does not mean that there is a severe

hurricane exactly every 6 years!

Metrics to describe hazard levels: Magnitude

• Amount of energy fuelling a natural event

• Example:

– Force of hurricane winds

– Amplitude of ground motion during an earthquake

– Amount of water flowing in a river during a flood

Frequency and Return

period

• Two ways to express the same facts:

– Frequency and return period are the inverse of one another

• Ex. Spring and fall heavy rains occur twice a year (frequency)

– So, every ½ year, spring and fall heavy rains occur

Low-magnitude events occur frequently (have a short period)

High-magnitude events are rare (have a long return period)

Frequency =
1

period

Period =
1

frequency

Frequent occurrences are low in magnitude; rare occurrences are high in

magnitude

The larger the event, the longer the return period (recurrence interval)

In general, inverse
correlation between

frequency and
magnitude of a process

5. Consequences of Hazards can be Minimized

• Primarily reactive in dealing with hazards
– Search and rescue
– Firefighting
– Providing emergency food, water, and shelter

• Need to increase efforts to anticipate disasters and their
effects
– Land-use planning limitations
– Hazard-resistant construction + building codes
– Hazard modification or control
– Disaster preparedness (e.g. Evacuation plans, insurance)
– Control through artificial structures

• Total losses are direct losses and losses related to human
actions

5. Consequences of Hazards Can Be Minimized:

Reactive Response

• Effects from a disaster can be
▪ Direct (felt by fewer individuals): people killed or

dislocated, buildings damaged, etc.
▪ Indirect (affect many more people): emotional distress,

donation of money or goods, taxes for recovery, etc.

• Recovery from disaster
▪ Emergency work
▪ Restoration of services and communication lines
▪ Reconstruction

Reducing Risk –

four pillars of emergency management

1. Response Short-term

– Immediate actions to put event under control

2. Recovery Middle-term

– Put situation back to normal

3. Mitigation Long-term

– Actions taken to minimize risk, damage

4. Preparedness Long-term

– Actions taken in advance to ensure people are ready

• New term added in response to climate change issues

– Adaptation Long-term

Potential Natural Disasters in

the Near Future:

“The Big One” (2015-2045)

• The US Geological

Survey’s Third Uniform California

Rupture Forecast (UCERF3)

predicts earthquake eruptions

and states that a magnitude 8.0

or larger earthquake has a 7

percent chance of occurring in

the next 30 years, at present.

• The odds of a magnitude 6.5–7.0

earthquake hitting went up 30

percent.

Wildfires in Canada and the United States

(2015-2050)

• Environmental scientists from

the Harvard School of

Engineering and Applied

Sciences (SEAS) predict that

by 2050, wildfire seasons will

be three weeks longer, twice as

smoky, and will burn a larger

portion of the West per year

• 30,000–50,000 wildfires

predicted to occur annually

Q: What has led to this dramatic increase in wildfire risk?

Canadian Trends

• The # of natural disasters

is increasing with time

• Communities are increasingly

vulnerable:

• Population growth

• Development in risky areas

• Degradation of natural

ecosystems

• Over-reliance on technology

Canadian Trends

• The # of natural disaster

fatalities is decreasing with

time

• Economic losses are mostly

due to weather-related

disasters

• Improved engineering

• Long-term prevention

• Extensive disaster

education

• Better warning systems

• Rapid response

Forecast, prediction, and warning of

hazardous events

• Uniformitarianism

– “The present is the key to the past”

• Human interaction has an effect on geologic processes

– “The present is the key to the future”

• Environmental Unity

– One action causes others in a chain of actions and events

Remember!

“Natural hazards are inevitable, but

natural disasters are not!”

… and the Oscar goes to …

… and the Oscar goes to …

CH. 2 – INTERNAL STRUCTURE OF THE EARTH

AND PLATE TECTONICS

Learning Objectives

• Describe the basic internal structure and processes of Earth.

• Summarize the various lines of evidence that support the theory of
plate tectonics.

• Compare and contrast the different types of plate boundaries.

• Explain the mechanisms of plate tectonics.

• Outline how plate tectonics has changed the appearance of Earth’s
surface over time.

• Compare and contrast the two fundamental processes that drive plate
tectonics.

• Link plate tectonics processes to natural hazards.

Learning Objectives
• Describe the basic internal structure and processes of Earth.
• Summarize the various lines of evidence that support the theory of
plate tectonics.
• Compare and contrast the different types of plate boundaries.
• Explain the mechanisms of plate tectonics.
• Outline how plate tectonics has changed the appearance of Earth’s
surface over time.
• Compare and contrast the two fundamental processes that drive plate
tectonics.
• Link plate tectonics processes to natural hazards.

Lithospheric Plates of the World

Two Cities on a Plate Boundary

• California straddles the
boundary between two
tectonic plates
• San Andreas fault: boundary

between North American and
Pacific plates

• Los Angeles and San Francisco
located on opposite sides of the

fault

• Movement of San Andreas
fault in 1906
• Caused major earthquake

• Earthquakes not understood at
the time

• Scientific investigations led to
identification of fault and new
understanding of earthquakes

Two Cities on a Plate Boundary

Topography is shaped

by Plate Tectonics!

Two cities on a Plate Boundary,

cont.

• San Andreas fault system

– Many moderate to large earthquakes in Los Angeles on this

fault

– Mountain

topography

in coastal California result of fault

– Earthquakes since 1906 have cost hundreds of lives and

billions of dollars in property damage

• Future of the fault

– Los Angeles and San Francisco will be side by side in 20

million years

– May be a shift in the plate boundary and a change in the

topography

Origin of the Sun and Planets – Solar Nebula

• The sun and planets were born from a rotating disk of cosmic gas and dust,

the solar nebula

• The flattened form of the disk constrains the planets:

– To move in the same direction as the disk

– To have their orbits in the same plane

Planetary accretion

Accretion stages:

1. Accretion into miniature planets (diameter < 1 km)

2. Collisions between miniature planets form a few large planets

• All planets formed at the same time (~4.6 billion years ago)

Earth’s Early History

Heat-generating processes during the formative years of the Earth

cause differentiation

Differentiation

Differentiation: process by which gravity causes denser

material to gradually migrate to the center of a planet

Density increasing

from surface to

center

www.phys.org

The Geoid

The shape that the surface of the oceans would

take under the influence of Earth’s gravity and

rotation alone

Surface of the Earth

Land

Model of the Earth

Sea

Geoid Ellipsoid

Differentiation of the Earth

Earth is differentiated

into layers based on:

– Density

– Strength

www.phys.org

Internal Structure of Earth

• Internal processes have incredibly important impacts

on the surface of the Earth

• Responsible for continents and ocean basins

• Oceans’ currents and distribution of heat carried by seawater

controlled by configuration of continents and ocean basins

• Responsible for regional landforms

• Earth is layered and dynamic

• Internal structure of Earth

• By composition and density

• By physical properties (strength)

Earth and its Interior

Layers based on density

Crust:

Silicon & Oxygen
Mantle:

Iron & Magnesium

Outer core:

Liquid iron

Inner core:

Solid iron

Layers based on density
Crust:
Silicon & Oxygen
Mantle:
Iron & Magnesium
Outer core:
Liquid iron
Inner core:

Solid iron

Less dense

Dense

Very dense

Internal Structure of Earth,

cont.

Earth’s structure:

• Outer core

– Liquid

– 2,000 km (1,243 mi.) in thickness

– Composition similar to inner core

– Density (10.7 g/cm3)

• Inner core

– Solid

– 1,300 km (808 mi.) in thickness

– High temperature

– Composed of iron (90 percent by

weight) and other elements (sulfur,

oxygen, and nickel)

The core is a

“heat battery”

• The Earth is cooling down

• Cooling of the liquid outer core

• The inner core is growing over

time as the outer core cools

and solidifies!

• Tremendous heat is given off

as the liquid outer core

solidifies and the inner core

cools. >10,000 Giga-watts!

Internal Structure of

Earth, cont.
• Mantle

– Solid

– 3,000 km (1,864 mi) in
thickness

– Composed of iron- and
magnesium-rich silicate
rocks

– Average density 4.5 g/cm3

• Crust
– Outer rock layer of Earth

– Density 2.8 g/cm3

– Moho discontinuity

– Separates lighter
crustal rocks from more
dense mantle

Layers based on density

Thin crust rich in silicon

and oxygen

Magnesium- and iron-

rich mantle

Iron-rich metallic core

Continental crust is

thicker and less dense

than oceanic crust

Continental vs.

Oceanic Crust

Continental Crust

• Average thickness:

35-70 km

• Less dense

• Older (up to 4 Ga)

• Typically composed of

granite

Oceanic Crust

• Average thickness: 6-

7 km

• More dense

• Younger (less than

200 Ma)

• Typically composed of

basalt

Material Deformation

• When materials are subjected to external forces, stress,

they deform or undergo strain

• Stress applied perpendicular => stretching under tension,

or contraction under compression

• Shear stress =

parallel to surface

Material Deformation – responding to stress

Internal Structure of Earth, cont.

The outer surface of the Earth consists of several

lithospheric plates moving relative to each other as rigid

bodies on a fluid substratum called the

asthenosphere

• Lithosphere

– Cool, strong outermost layer of Earth (crust and upper mantle)

– Crust embedded on top

• Asthenosphere

– Below lithosphere

– Hot, soft/ductile slowly flowing layer of weak rock

– Higher water content and hotter

Layers based on Strength

Gaseous atmosphere

Liquid hydrosphere

Rigid lithosphere

Soft plastic asthenosphere

Stiff plastic mesosphere

Liquid outer core

Solid inner core

Internal Structure of Earth, cont.

The boundary between lithosphere and asthenosphere not defined by

a difference in chemical compositions, but in mechanical properties

(i.e. the rigidity of the material, how the material deforms under stress).

CONTINENTAL

PLATE

OCEANIC

PLATE
MANTLE

LITHOSPHERE

CRUSTAL

LITHOSPHERE

ASTHENOSPHERE

Tectonic plates are lithospheric plates

Tectonic plates

are lithospheric

plates “floating”

on top of the

asthenosphere

Lithosphere –

asthenosphere

boundary at a

depth of ~100 km

Buoyancy
• Earth can be described as a series of layers where less dense

material floats on top of denser material

– Low-density crust floats on top of the denser mantle

– Mantle floats on top of the very dense core

root

load

Isostasy
Surface elevation represents a balance between forces:

– Gravity : pushes plate into mantle

– Buoyancy : pushes plate back to float higher on mantle

Isostatic equilibrium describes this balance.

Isostasy is compensated after a disturbance.

Adding weight pushes lithosphere down

Removing weight causes isostatic rebound

Compensation is slow, requiring asthenosphere to flow.

root
load

Isostasy in Canada

• ~18,000 years ago,
Canada was buried under
a continental glacier with
ice thickness ~5 km
around Hudson Bay

• The weight of the ice
sheet caused the land to
sink more than 1 km

• 10,000 years ago the ice
sheet had melted and
retreated

Heat Transfer

Heat can be transmitted through solids and fluids by

conduction, through fluids by convection, and by radiation.

Heat Transfer

On a planetary scale, the same processes are active!

– Heat from the interior of Earth flows

to the surface by conduction

– In the mesosphere and

asthenosphere, heat is redistributed

by flow of plastic solids

– Hot, less-dense materials rises

– Cold, denser material sinks creating

convection cells

Internal Structure of Earth, cont.
• Convection

– Earth’s internal heat causes magma to heat up and become less dense

– Less dense magma rises

– Cool magma falls back downward

Internal Structure of Earth, cont.
• Convection
– Earth’s internal heat causes magma to heat up and become less dense
– Less dense magma rises
– Cool magma falls back downward

How do we infer the structure of the Earth?

How do we infer the structure of the Earth, cont.

• Seismology!

– Study of earthquakes

– Information on wave movement

• Earthquakes cause seismic energy to move through Earth

(more later)

– Some waves move through solids, but not liquids

– Some waves are reflected

Incident

ray

Reflected

ray

How do we infer the structure of the Earth, cont.
• Seismology!
– Study of earthquakes
– Information on wave movement
• Earthquakes cause seismic energy to move through Earth
(more later)
– Some waves move through solids, but not liquids
– Some waves are reflected

– Some waves are refracted

Global seismic observations

Quick intro. – Seismic waves

P waves (Primary waves): compressional motion, 6-8 km/s

S waves (Secondary waves): shear motion, 3-5 km/s. Do

not pass through liquids

Surface waves: travel along surface of earth, < 3-4 km/s

S-waves and the outer core

• S-waves do not propagate in a liquid

• Liquid cannot support shear motions

• This is how we infer that the outer core is liquid

• S-waves do not propagate through the outer core

Seismic Shadow Zones

Seismic tomography can also tell us the locations

of hot and cold regions in the mantle

(credit: Global Seismology Group / Berkeley Seismological Laboratory)

CH. 3 – EARTHQUAKE

S

https://www.usgs.gov/news/updat

e-magnitude-71-earthquake-

southern-california

https://www.usgs.gov/news/update-magnitude-71-earthquake-southern-california

Earthquake

Alert!

M6.4 and M7.1

earthquakes occurred

in Southern California

within 36 hours of

each other, 11 km

apart

Learning Objectives

• Compare and contrast the different types of faulting.

• Explain the formation of seismic waves.

• Summarize the processes that lead to an earthquake and the release of
seismic waves.

• Differentiate between the magnitude scales used to measure
earthquakes.

• Identify global regions at most risk for earthquakes, and describe the
effects of earthquakes.

• Describe how earthquakes are linked to other natural hazards.

• Explain how human beings interact with and affect earthquake hazards.

• Propose ways to minimize seismic risk and suggest adjustments we can
make to protect ourselves.

Energy and Natural Hazards

2011 Tohoku Earthquake

• Japan located just 200 km (~124 mi) west of Japan
Trench
• Pacific plate is subducting beneath Eurasian plate (9 cm/yr)

• Experiences frequent large earthquakes

• March 11, 2011
• Strongest recorded earthquake to hit Japan

• Significantly greater than considered possible
• Released about 600 million times more energy than bomb on Hiroshima

• Well engineered buildings helped reduce the loss of lives due to
structural collapse

• Greatest loss of life was due to tsunami

Shaking and Damage During the Tohoku Earthquake

Introduction to Earthquakes

• What is an earthquake?
• The sudden slip on a fault (release of elastic energy), and the

resulting ground shaking and radiated seismic energy caused by the

slip {USGS, 2002}

• People feel approximately 1 million earthquakes a year
• Few are noticed very far from the source

• Even fewer are major earthquakes

• Most earthquakes occur along plate boundaries

Earthquake Distribution

Faults and Faulting

• Earthquakes occur along faults
• Plane of weakness in Earth’s crust

• Semi-planar fracture or fracture system where rocks are broken
and displaced

• Fracture (crack) in the earth, where the two sides of the earth move
past each other

• Centuries-old mining terminology used
• Footwall

• Block below the fault plane

• Miner would stand here

• Hanging wall

• Block above the fault plane

• Hang a lantern here

Basic Fault

Features

Footwall
• Block below the fault plane
• Miner would stand here

Hanging wall
• Block above the fault plane
• Hang a lantern here

Faults and Faulting, cont.

• Faulting – process of fault rupture
• Similar to sliding one rough board past another

• Slow motion due to friction

• Stresses the rocks along the fault

• Rocks rupture and displaced when stress exceeds strength of rocks

• Stress
• Force that results from plate tectonic

movement

s

• Tensional

• Compressional

• Shearing

• Strain
• Change in shape or location of the rocks due to the stress

Faults ≠ Plate boundaries

• However, most faults occur along plate boundaries

• Fault types

– Distinguished by direction of rock displacement

• Three basic types:

1. Dip-slip

a) Normal

b) Reverse

2. Strike-slip

a) right-lateral

b) left-lateral

3. Oblique slip

Normal dip-slip
• Vertical motion

• Hanging wall moves down

relative to footwall

Reverse dip-slip
• Vertical motion

• Hanging wall moves up relative
to footwall

Strike-slip • Crust moves in horizontal direction

Faults and Faulting, cont.

• Blind faults do not extend to the surface

Types of Plate Boundaries and Stress

• Divergent = Extensional Stress >> Normal Faulting

• Convergent = Compressional Stress >> Thrust
or Reverse Faulting

• Transform = Shear Stress >> Strike-Slip Faulting

Block diagram of fault

surface

Faults are not simple planar

surfaces!

Faults are complex zones of

breakage where rough and

interlocking rock is held

together over an irregular

surface.

Stress builds up over many

years before enough energy

is stored to allow rupture on

the fault.

Elastic Rebound Theory
Gradual build up of stress along a fault until the strength of the rock is

exceeded, resulting in a release of energy in the form of an earthquake

The Earthquake Cycle

• Change in strain
• Accumulation before an earthquake

• Drop after an event

• Three or four stages
1. Long period of inactivity

2. Accumulated elastic strain produces small earthquakes

3. Foreshocks
• Hours or days before large earthquake

• May not occur

4. Mainshock
• Major earthquake

• Includes aftershocks: few minutes to a year after

Elastic Rebound
Rocks deform elastically until a

critical point is reached and the

fault slips, releasing the stored

elastic energy

Time 1

Time 2

Time 3

Time 4

The Earthquake Cycle, cont.

Epicenter

• Given by news reports

• Location on surface
above the rupture

• Focus (hypocenter)
• Point of initial breaking

or rupturing

• Displacement of rocks
starts here
• Propagates up, down,

and laterally along the
fault plane

• Produces shock waves,
called seismic

waves

(cause ground shaking)

Seismic Waves

• Caused by a release of energy from rupture of a fault

• Body waves: travel through the body of the Earth

P waves, primary or compressional waves

– Move fast with a push/pull motion

– Can move through solid, liquid, and gas

S waves, secondary or shear waves

– Move slower with an up/down motion

– Can travel only through solids

P waves, primary or compressional waves

– Body waves, travel through the body of the Earth
– Move fast with a push/pull motion
– Can move through solid, liquid, and gas

P waves, primary or compressional waves

– Velocity depends on density

and compressibility of the

materials through which they

pass

– Greater resistance to

compression, greater the

velocity

– Seismic waves pass

through packed atomic

structures

– Velocity through igneous rocks

(eg. granite) ~5.0

km/s

– Velo. in sed. rocks (eg.,

sandstone) ~3.0 km/s

S waves, secondary or shear waves

– Body waves, travel through the body of the Earth
– Move slower with an up/down motion
– Can travel only through solids

S waves, secondary or shear waves

– Transverse waves that

propagate by shearing

particles at right angles to the

direction of propagation in the

vertical and horizontal plane

– Velocity depends on density

and resistance to shearing of

materials

– Velo. in igneous rocks ~ 3.0

km/s

– Velo. in sedimentary rocks ~1.7

km/s

Seismic Waves, cont.

Surface waves: move along

Earth’s surface
• P and S waves that reach the

surface

• Travel more slowly than body

waves

• Complex horizontal and vertical

ground movement

Rayleigh Waves
• Rolling motion

• Responsible for most of the

damage near epicenter

• Shaking produces both

vertical and horizontal

movement

Seismic Waves, cont.

Surface waves: move
along Earth’s surface

• P and S waves that reach the
surface

• Travel more slowly than body
waves

• Complex horizontal and
vertical ground movement

Love Waves
• Horizontal ground shaking

• Faster than Rayleigh
waves

• Do not move through water
or air

• Very hazardous!

Wave direction

Seismic Waves and Wave Attributes

Properties of Seismic Waves:

• Amplitude: height of wave

• Wavelength: distance between successive wave peaks

• Period [s]: time between wave peaks (= 1/frequency)

• Frequency [Hz]: number of wave peaks in one second

Seismic Waves and Wave Attributes
Properties of Seismic Waves:

• Attenuation: amplitude of seismic waves decreases with

increasing distance from the hypocenter

– More pronounced for high-frequency waves

– Less pronounced for low-frequency waves

How do we detect and record seismic waves?

Horizontal component Vertical component

Before computers…

Modern 3-component seismograph station

3 orthogonally aligned seismometers:

– Veritcal

– North-south

– East-west

Seismogram
(a recording of the ground motion)

P

S

Analysis of seismic

records allows

seismologists to

identify the different

kinds of seismic

waves generated by

fault movement

Distance to Epicenter

Use difference between first P and S wave arrival times:

– P waves will appear first

– Seismographs across globe record arrivals of waves to station sites

– Distance to epicenter can be found by comparing travel times of the
waves

Distance to

Earthquake
Epicenter

Note:

P-wave first

S-wave second

Surface waves last

Time lag between P and S-wave

arrival is called Δt, or the S-P time.

Ex. 1994 M 6.7

Northridge earthquake

Calculating Epicentral Distance

P wave has velocity VP ; S wave have velocity VS

VS < VP

Both originate at the same place – the hypocenter – and travel the same distance, but

the S wave takes longer to arrive than the P wave.

Time for S wave to travel a distance D:

Time for P wave to travel a distance D:

The time difference between them is:

Now solve for the distance D:

Time =
Distance

Velocity

T
S

=
D

V
S

T
P

=
D

V
P

(T
S
-T

P
) =
D

V
S


D

V
P

= D
1

V
S


1

V
P

æ

è
ç

ö

ø
÷ = D

V
P

-V
S

V
P
V
S

æ
è
ç
ö

ø
÷

𝐷 =
𝑉𝑃𝑉𝑆
𝑉𝑃 − 𝑉𝑆

𝑇𝑠 − 𝑇𝑝

Locating an Earthquake

• Location of epicenter
• At least three stations

are needed to find
exact epicenter

• Distances from
epicenter to each
station are used to
draw circles
representing possible
locations

• The place where all
three circles intersect
is the epicenter

• Process is called
triangulation

Tectonic Creep and Slow Earthquakes

• Tectonic creep: gradual movement such that

earthquakes are not felt
– Can produce slow earthquakes

– Also called fault creep

• Can slowly damage roads, sidewalks, and building

foundations

• Can last from days to months

https://seismo.berkeley.edu/blog/2008/10/14/the-hayward-fault.html

https://seismo.berkeley.edu/blog/2008/10/14/the-hayward-fault.html

Earthquake Shaking

• Shaking experience depends on:

1. Earthquake magnitude

2. Location in relation to epicenter and direction of rupture

3. Local soil and rock conditions

• Strong shaking from a moderate magnitude or higher

CH. 2 – INTERNAL STRUCTURE OF THE EARTH

AND PLATE TECTONICS

Learning Objectives

• Describe the basic internal structure and processes of Earth.

• Summarize the various lines of evidence that support the theory of
plate tectonics.

• Compare and contrast the different types of plate boundaries.

• Explain the mechanisms of plate tectonics.

• Outline how plate tectonics has changed the appearance of Earth’s
surface over time.

• Compare and contrast the two fundamental processes that drive plate
tectonics.

• Link plate tectonics processes to natural hazards.

Learning Objectives
• Describe the basic internal structure and processes of Earth.
• Summarize the various lines of evidence that support the theory of
plate tectonics.
• Compare and contrast the different types of plate boundaries.
• Explain the mechanisms of plate tectonics.
• Outline how plate tectonics has changed the appearance of Earth’s
surface over time.
• Compare and contrast the two fundamental processes that drive plate
tectonics.
• Link plate tectonics processes to natural hazards.

Lithospheric Plates of the World

Earth and its Interior

Two Cities on a Plate Boundary

• California straddles the
boundary between two
tectonic plates
• San Andreas fault: boundary

between North American and
Pacific plates

• Los Angeles and San Francisco
located on opposite sides of the
fault

• Movement of San Andreas
fault in 1906
• Caused major earthquake

• Earthquakes not understood at
the time

• Scientific investigations led to
identification of fault and new
understanding of earthquakes

Plate Tectonics – Shift happens!

• Large-scale geologic processes that deform Earth’s

lithosphere

• Produce

landforms such

as ocean

basins,

continents

, and

mountains.

• Processes are

driven by forces

within Earth

Movement of the Tectonic Plates

• Lithosphere is broken into pieces

• Lithospheric plates or tectonic plates

• Plate tectonics

• Plates move relative to one another

• Plates are created and destroyed

• Boundaries between lithospheric plates are geologically

active areas

• Responsible for several of the most devastating natural

hazards, such as earthquakes and volcanoes

Earth’s Plates

THREE types of plate boundaries:

1. Divergent

2. Convergent

3

. Transform

Earth’s Plates

Location of volcanoes and earthquakes is not random!

Fit of the Continents

• Antonio Snider-Pelligrini (1858),

a geographer cut out a map of

Africa and South America

suggesting they were connected

at one time

• Other physical evidence based

on observation (maps, fossils

etc.) was used by Wegener

Continental Drift Hypothesis

• Alfred Wegener proposed
the hypothesis of
continental drift in 1915

• Theory based on congruity
of the shape of the
continents and similarity of
fossils in South America +
Africa

• Theory not accepted
because could not explain
how continents moved

Alfred Wegener Institute

Movement of the Tectonic Plates, cont.

• Seafloor spreading

• Explained mechanism for plate tectonics

• At mid-ocean ridges new crust is added to edges of

lithospheric plates

• Continents are carried along plates

• Crust is destroyed along other plate edges

• Subduction

zones

• Earth remains constant, never growing or shrinking

Model of Plate Tectonics

The tectonic cycle – the “conveyor belt” model

1

2

3

The lithosphere moves laterally as if it were a conveyor belt

Direction of motion

The lithosphere moves laterally as if it were a conveyor belt

Direction of motion

Convection loop

Movement of the Tectonic Plates, cont.

• Sinking plates generate volcanoes and earthquakes

• Sinking ocean plates are wet and cold

• Plates come in contact with hot

asthenosphere

• Plates melt to generate magma

• Magma rises to produce

volcanoes

• Volcanic arcs

• Earthquakes occur along the path of the descending plate

• Wadati-Benioff zones

• Plate collides with another plate

• Denser plate dives under the

less-dense plate and is recycled

Denser plate: subducting plate

Less-dense plate:

overriding plate

Subduction Zone
• Plate collides with another plate

• Denser plate dives under the
less-dense plate and is recycled

Plate Tectonics – Shift happens!

• Dark blue linear features = deep water

• Deep trenches

where plates

re-enter the

asthenosphere

• Surface

expression of

subduction

zones

Plate Tectonics – Shift happens!

• Light blue linear features = shallow water

• Along mid-

oceanic

ridges

• Bulge caused

by

asthenosphere

flowing

upwards

• Surface
expression of

spreading

centers

Movement of the Tectonic Plates, cont.

• Plate tectonics is a unifying theory

• Explains a variety of phenomena

• Evolutionary change

• How Earth works

• Direction of plate movement

• Distribution of earthquakes and volcanoes

• Similarities among fossils on different continents

• Changes in Earth’s magnetism

• Convection likely drives plate tectonics

Plate Movement

Hypothetical convection cells that may drive plate tectonics

Plate Movement

Internal Earth mostly solid, NOT liquid! Mantle is a

visco-elastic material

Types of Plate Boundaries

Defined by the relative movement of the plates on either

side of the boundary

Types of Plate Boundaries, cont.

Divergent Boundaries

• Plates move apart during seafloor spreading

• Magma from asthenosphere rises

Divergent Boundaries

Plates are pulled apart

under tension at

divergent zones:

Reduction in

pressure on

superheated

asthenosphere rock

Liquifies and rises

Buildup of magma

and heat causes

expansion and

elevation of

overlying

lithosphere

Divergent Boundaries

Gravity pulls the dome

downward:

Creating downward

down-dropped rift

valleys

Faulting progresses,

magma rises up through

cracks to build

volcanoes

Rifting + volcanism

continues, seafloor

spreading takes over,

down-dropped linear rift

valley fills with ocean

New sea is born

Divergent Boundaries around the World

Convergent Plate Boundaries: Subduction Zones

What pulls the

plate down?

Convergent

Plate

Boundaries:

Collision Zones

Gros Morne National Park, Newfoundland

500 million years ago, a large piece of oceanic lithosphere

was scraped off the downgoing plate as it was subducting

Tabelands – access

to complete thickness

of the oceanic

lithosphere from the

upper mantle to the

Earth’s surface

3D view of different tectonic environments

Continent-Continent Collision

Credit: USGS

Continental collision between the

Indian and Asian plates

Tectonic

map

showing

India

pushing

into Asia

Transform Plate Boundaries

Plates slide past each other

Divergent Boundaries & Transform Faults

Rates of Plate Motion

• Plate motion is fast (geologically)
– Plates move a few centimeters per year

• Movement may not be smooth or steady

• What happens when the rough edges along the plate
move quickly?

• Plates can displace by several meters during a great
earthquake
– Such as with San Andreas fault

North American Plate Boundary

Subduction in California

Plate tectonics – Supporting evidence

• Oceanography

– Magnetization patterns on seafloor

– Age of ocean basins

– Bathymetry

• Earthquake hypocenters and epicenters

• Matching of fossils and rock types across

continents

A Detailed look at Seafloor Spreading

• Mid-ocean ridges discovered by Harry H. Hess

• Validity of seafloor spreading established by:

1) Identification and mapping of oceanic ridges

2) Dating of volcanic rocks on the floor of the ocean

3) Understanding and mapping of the paleomagnetic

history of ocean basins

https://www.e-

education.psu.edu/earth520/node/1811

Ocean bottom is on average about 3.8 km deep,

with two main exceptions:

• Continuous mountain ranges

— several thousand feet in elevation from ocean floor

— extend more than 65,000 km along ocean floors

– Volcanic mountains that form at spreading centers,

where plates pull apart and magma rises to fill gaps

• Narrow trenches extend to depths of more than 11 km

– Where tops of subducting plates turn downward

to enter mantle

Evidence of Plate Tectonics: Seafloor Topography

Ocean bottom is on average about 3.8 km deep,
with two main exceptions:

• Continuous mountain ranges
— several thousand feet in elevation from ocean floor

— extend more than 65,000 km along ocean floors

– Volcanic mountains that form at spreading centers,
where plates pull apart and magma rises to fill gaps

• Narrow trenches extend to depths of more than 11 km
– Where tops of subducting plates turn downward
to enter mantle
Evidence of Plate Tectonics: Seafloor Topography

Paleomagnetism

• Earth’s magnetic field can
be represented by a dipole
• Forces extend from North to

South Poles

• Magnetic poles do not
coincide exactly with
geographic poles

• Movements of iron-rich fluid
generate a magnetic field
around Earth
– Which layer of Earth is

responsible for this?

Paleomagnetism

• Earth’s internal magnetic
field NOT constant through
time

• Over a few years: magnetic
poles wander around the
geographic poles

• Polarity reversal ~ every
few 100,000 yrs
– North magnetic pole south

magnetic pole

Normal

polarity

(eg. Today)

Paleomagnetism, cont.

• Magnetic field has permanently magnetized some surface rocks at
the time of their formation

– Iron-bearing minerals orient themselves parallel to the
magnetic field at the critical temperature known as Curie
Point

– Thermoremnant magnetization

Paleomagnetism is the
study of magnetism of
rocks at the time their
magnetic signature is
formed

Paleomagnetism, cont.

• Some volcanic rocks show

magnetism in opposite

direction as today

• Earth’s magnetic field has

reversed

• Cause is not well known

– Reversals are random

– Occur on average every few

hundred thousand years

Paleomagnetism, cont.

• Magnetic stripes

– Geologists towed

magnetometers along ocean

floor to measure magnetic

properties of rocks

– When mapped, the ocean

floor had stripes

• Areas of “regular” and “irregular”

magnetic fields

• Stripes were parallel to oceanic

ridges

• Sequences of stripe width

patterns matched the

sequences established by

geologists on land

Magnetic Anomalies on the Seafloor

• Using the magnetic anomalies, geologists can infer

ages for the ocean rocks

– Seafloor is no older than 200 million years old

• Spreading at the mid-ocean ridges can explain stripe

patterns

– Rising magma at ridges is extruded

oCooling rocks are normally

magnetized

oField is reversed with new rocks that push old rocks away

Magnetic Reversals and Seafloor Spreading

Notice symmetry on either side of the ridge!

Magnetism and Age of the Seafloor

Map of magnetically striped Pacific

Ocean floor off Vancouver Island:

– Black areas are normally

magnetized

– Yellow areas point to reverse

polarity

Systematic increases in seafloor depth

• Ocean floor depths increase systematically with seafloor

age, moving away from mid-ocean ridges

• Why? As oceanic crust gets older, it cools and becomes

denser, therefore sinking lower into mantle.

Seafloor Topography and Age

Age of the Ocean Floor

The present ocean floors are no older than

200 million years, WHY??

Age of the Ocean Floor, cont.

• Subduction!

• Thick, buoyant, continental crust stable at Earth’s surface

• Continents form by:

• Accretion of sediments

• Addition of volcanic materials

• Collisions of tectonic plates carrying continental landmasses

• Pattern of magnetic stripes allows us to reconstruct how

plates and continents embedded in them have moved

throughout history

Paleomagnetism, cont.

• Hot spots

• Volcanic centers resulting from hot materials from deep in

the mantle

• Materials move up through mantle and overlying plates

• Found under both continental and oceanic crust

• Continental: Yellowstone National Park

• Oceanic: Hawaiian-Emperor Chain

• Plates move over hot spots creating a chain of island volcanoes

• Seamounts are submarine volcanoes

Hawaiian Hot

Spot

Pangaea and Present Continents

• Movement of plates is responsible for present shapes
and locations of continents
• 180 million years ago there was the break-up of

Pangaea

• Supercontinent extending from pole to pole and halfway around Earth

• 50 Million years ago India crashed into China creating the
Himalayas

• Reconstruction of Pangaea and recent continental
drift clears up:

• Fossil data difficult to explain with separated continents

• Evidence of glaciation on several continents

Two

Hundred

Million

Years of

Plate

Tectonics

180 million years ago

135 million years ago

Two
Hundred
Million
Years of
Plate
Tectonics

65 million years ago

Paleontological Evidence for Pangaea

Ancient Mountain Ranges

The same sequence of rocks is found in

North America, Great Britain, and Norway.

The pattern does not make sense with the

continents in their current configuration.

Matching rock types and rock ages

Glacial

Evidence for

Pangaea

• Glaciers carve the rock as they

move.

• Scientists can determine the

direction of movement

Reconstructed ice sheet on

Gondwana.

How Plate Tectonics works: Putting it Together

• Two possible driving mechanisms for plate tectonics
• Ridge Push and slab pull

• Ridge push is a gravitational push away from crest of
mid-ocean ridges

• Slab pull occurs when cool, dense ocean plates sink
into the hotter, less dense asthenosphere
• Weight of the plate pulls the plate along

• Evidence suggests that slab pull is the more
important process

Push and Pull in Moving Plates

Plate Tectonics and Hazards

• Divergent plate boundaries (Mid-Atlantic Ridge) exhibit
earthquakes and volcanic eruptions

• Transform boundaries (San Andreas Fault) have great
earthquake hazards

• Convergent subduction plate boundaries are home to
explosive volcanoes and earthquake hazards

• Convergent collision plate boundaries have high
topography (Tibetan Plateau) and earthquakes

• Internal structure of Earth can be divided into layers

or concentric shells, based on either composition or

physical properties.

• The uppermost physical layer of Earth is known as

the lithosphere and is relatively strong and rigid

compared with the soft asthenopshere underlying it.

• A convection cell is a temperature-driven circulation

pattern that is assumed to operate within Earth and

may be involved in driving plate tectonics.

Chapter 2 Summary

• The lithosphere is broken into large pieces called

tectonic plates that move relative to one another.

• The three types of plate boundaries are divergent,

convergent, and transform faults.

• Evidence supporting plate tectonics theory includes

seafloor spreading, continental drift, the configuration

of hot spots and chains of volcanoes, and Wadati-

Benioff zones.

Chapter 2 Summary, cont.

• Convection currents in Earth’s liquid outer core

generates a magnetic field that is sufficiently strong

to be recorded in rocks that contain magnetic

minerals.

• The seafloor spreading hypothesis proposed a

mechanism for continental drift.

• Seafloor spreading is confirmed using the

paleomagnetic signature of the seafloor centered

around the mid-ocean ridges.

Chapter 2 Summary, cont.

• The age of the seafloor is younger than 200 million
years old, which is 20 times younger than the age of
continents.

• Hot spots are plumes of hot rock that rise from deep
in the mantle and cause volcanoes above them at
Earth’s surface.

• Alfred Wegener’s continental drift hypothesis
suggested that all of Earth’s continents were in the
past assembled in a single enormous continent,
known as Pangaea.

Chapter 2 Summary, cont.

• With the validation of the seafloor spreading,

continental drift was confirmed and several long-

standing geologic problems have been resolved.

• The driving forces in plate tectonics are ridge push

and slab pull.

• Plate tectonics is extremely important is determining

the occurrence and frequency of volcanic eruptions,

earthquakes, and other natural hazards.

Chapter 2 Summary, cont.

• Divergent plate boundaries are linked to earthquakes

and volcanic eruptions, but the risk is low because most

do not occur on land.

• Transform boundaries are linked to earthquakes and

represent and appreciable risk as these faults occur on

land and stretch for long distances, often through

populated regions.

• Convergent plate boundaries are zones of greatest risk

as these are linked to the largest recorded earthquakes,

explosive volcanic eruptions, and tsunamis.

Chapter 2 Summary, cont.

CH. 4 – TSUNAMIS

Energy and Natural Hazards

No subduction zones!

No faults that could

create even a large

tsunami, let alone a

“megatsunami”

Learning Objectives

• Explain the process of tsunami formation and development.

• Locate on a map the geographic regions that are risk tsunamis.

• Synthesize the effects of tsunamis and the hazards they pose
to coastal regions.

• Summarize the linkages between tsunamis and other natural
hazards.

• Tsunamis are not caused by or affected by human activities,
but damages are compounded as coastal populations increase.

• Discuss what nations, communities, and individuals can do to
minimize the tsunami hazard.

Introduction to Tsunamis

• Tsunami is Japanese for “harbour wave”
• Caused by a sudden vertical displacement of ocean

water

• Triggered by:
• Large earthquakes that cause uplift or subsidence of sea floor

• Underwater landslides

• Volcano Flank Collapse

• Submarine volcanic explosion

• Asteroids

• Can produce Mega-tsunami

• “Tidal Wave” – misnomer!
• Tsunamis are not related to tides

Some Historic Tsunamis

General Wave Attributes

Properties of Seismic Waves:

• Amplitude: height of wave

• Wavelength: distance between successive wave peaks

• Period [s]: time between wave peaks (= 1/frequency)

• Frequency [Hz]: number of wave peaks in one second

Tsunami Waves

• Series of waves with long wavelengths (20 km to over 800 km)

and long periods (10 minutes to 1 hour)

• The restoring force is gravity (compare with seismic waves:

elastic waves where restoring force is springiness of rocks)

• Velocity depends on water depth:

g is gravitational acceleration (9.8 m/s2)

d is water depth

v = gd

Tsunami vs. Wind-caused waves

• Wind-caused waves

– water rotates in circles

– short wavelength

– short period

• Tsunami

– flow as massive sheets of

water

– long period

– long wavelength (the

longer the wavelength, the

slower the wave loses

kinetic energy)

How do Earthquakes Cause a Tsunami :

Point

source

• Volcano- and landslide-caused tsunami

• Trigger is a point source

– Energy flows away radially, high attenuation, local damage

Tsunami waves

propagate radially

when it is a point

source

How do Earthquakes Cause a Tsunami –

Fault Source
Linear source:

fault (on seafloor)

that ruptures

Tsunami waves

propagate mainly in

direction

perpendicular to fault

Low attenuation:

potential for damage

far from source

How do Earthquakes Cause a Tsunami?

• Two mechanisms:

– Seafloor movement (more common)

– Triggering a landslide

• Takes an earthquake of M 7.5 or greater

– Creates enough displacement of the seafloor

– Upward or downward movement displaces the entire mass of water

– Starts a four-stage process

How do Earthquakes cause a Tsunami?

1. Earthquake uplifts or downshifts the seafloor

• Rupture uplifts the seafloor

• A dome forms on the surface of the water above the fault

• Dome collapses and generates the

tsunami wave

• Waves radiate outward (like a pebble in a pond)

2. Tsunami moves rapidly in deep ocean

• Can travel 720 km per hour

• Spacing (frequency) of crests is large and small amplitude

• Boats in open ocean don’t notice the tsunami waves

Characteristics of Ocean Waves

• Characteristics common to all waves propagating in the

open ocean:

– Water moves in forward-rotating circles

– Diameter of circles decreases with depth

– Negligible for depth > L/2

In open ocean:

H < 1m

Shoaling

• Occurs when waves interact with the seafloor near

the shoreline

• Interaction starts when depth < L/2

• Friction slows wave down

• Wavelength decreases

– Energy is concentrated in a shorter length

• Amplitude increases

– Wave breaks

Near shore:

H ~ 6-15 m

Characteristics of Ocean Waves

Longer

wavelength in

deep water

Shorter

wavelength in

shallow water

How do Earthquakes cause a Tsunami?

3. Tsunami nears land, loses speed, gains height
– Depth of ocean decreases, slowing tsunami waves

45 km per hour

– More water piles up increasing amplitudes and frequency

4. Tsunami moves inland destroying everything in its path
– Can be meters to tens of meters high

– Often arrives as a quick increase in sea level

– Trough may arrive first, exposing seafloor

– Runup, furthest horizontal and vertical distance of the largest wave

– Water returns to ocean in a strong, turbulent flow

– Edge waves may be generated parallel to the shore

– Second and third waves may be amplified

How do Earthquakes cause a Tsunami?

• Offshore earthquakes can
cause tsunamis to go
toward land and out to sea
• Uplifted dome of water splits in

two waves

• Distant tsunami
• Travels out to sea and travels

long distances with little loss of
energy

• Local tsunami
• Travels quickly towards land

• People have little time to react

How do landslides cause a tsunami?

• Submarine landslides occur

when landslides occur

underneath the water

– Displaces water vertically causing

tsunamis

• On land, rock avalanches from

mountains can cause tsunami

– Example: Lituya Bay, Alaska

– 30.5 million cubic meters of rock

fell into ocean

– Bay water surged to 524 m (1790

ft.) above normal

Geographic Regions at Risk from Tsunamis

• All

oceans

and some lake shorelines have some risk

– Greater risk is for coasts near sources of tsunamis

– Which are??

• Greatest risk is to areas near or across from

subduction zones

– Example: Cascadia zone, Chilean Trench, off Coast of Japan

Where do the most tsunamis occur?

a) Indian and Atlantic

oceans

b) Atlantic and Pacific oceans

c) Pacific and Indian oceans

d) Indian and Arctic oceans

e) Arctic and Atlantic oceans

Ring of Fire = Subduction zones

Where do the most tsunamis occur?

a) Indian and Atlantic

oceans

b) Atlantic and Pacific

oceans

c) Pacific and Indian

oceans

d) Indian and Arctic

oceans

e) Arctic and Atlantic

oceans

Why is the tsunami hazard in the Atlantic so low?

Tsunamis arrive as the leading edge of an elevated mass of water

– Similar to a very rapidly rising tide

– NOT breaker shape

Runs up and over the beach, floods inland for many minutes

Near shore topography (bays,

inlets) can focus the energy and

locally create enormous waves

Why does water often recede ahead of

a tsunami wave?

Water recedes

Direction of

propagation of

tsunami wave

e
q
u
il
ib

ri
u
m

Trough hits

shore first

Why does water often recede ahead of
a tsunami wave?

Water runs up

Direction of
propagation of
tsunami wave
e
q
u
il
ib
ri
u
m

Peak follows a

few minutes later

1960 Chile M 9.5 earthquake

• Most powerful earthquake ever measured

Earthquake-generated tsunami: 1960 Valdiva M 9.5

Case Study : Sumatra

• 26 December, 2004

• M9.2 megathrust earthquake

• 3-4 min. of ground shaking,
250 km offshore

• Death and destruction in 13
countries:
– 198,000 deaths Indonesia

– 30,000 deaths Sri Lanka

– 11,000 deaths India

– 6000 deaths Thailand

• 1200 km long fault

• Seafloor offsets of up ~10 m

• Travelled 1.5 km inland

Case Study – Sumatra

• Megathrust event
– Most lethal tsunami in recorded

history

– No warning system in Indian Ocean

– Few people knew what tsunami
meant prior to event

• Education (or lack of) was a
major reason for so many
deaths
– Many did not know how to

recognize a tsunami

– Many went to beach to watch

– Few knew what to do

– Tourists and first-generation residents

2004 Sumatra Tsunami killed people

on both sides of Indian Ocean

2004 Sumatra Earthquake

2004 Sumatra Earthquake, cont.
• Those that were educated

• Scientists on beach in Sri Lanka
• Noticed the sea level drop

• Sounded warning for those that went to beach to watch

• Animal behavior
• Elephants started trumpeting about time of earthquake

• Ignored handlers and headed up hill

• Education of tsunami could have saved thousands more, especially
with the distant tsunamis

June 23, 2004 December 28, 2004

Effects of Tsunamis and Linkages with Other

Natural Hazards

• Primary effects

– Inundation of water and resulting flooding and erosion

– Shorten the coastline

– Debris erodes both landscape and human structures

• Secondary effects

– Fires

– From ruptured gas lines or other sources

– Contaminated water supplies

– Floodwaters, wastewater treatment plants, rotting animal carcasses and

plants

– Disease

– Come in contact with polluted water or soil

• Coastline erosion

CH.3 – EARTHQUAKES

https://www.usgs.gov/news/updat

e-magnitude-71-earthquake-

southern-california

https://www.usgs.gov/news/update-magnitude-71-earthquake-southern-california

Learning Objectives

• Compare and contrast the different types of faulting.

• Explain the formation of

seismic waves

.

• Summarize the processes that lead to an earthquake and the release of
seismic waves.

• Differentiate between the magnitude scales used to measure

earthquakes.

• Identify global regions at most risk for earthquakes, and describe the
effects of earthquakes.

• Describe how earthquakes are linked to other natural hazards.

• Explain how human beings interact with and affect earthquake hazards.

• Propose ways to minimize seismic risk and suggest adjustments we can
make to protect ourselves.

Basic Fault

Features

Footwall
• Block below the fault plane
• Miner would stand here

Hanging wall
• Block above the fault plane
• Hang a lantern here

Faults ≠ Plate boundaries

• However, most faults occur along plate boundaries

• Fault types

– Distinguished by direction of rock displacement

• Three basic types:

1. Dip-slip

a) Normal

b) Reverse

2. Strike-slip

a) right-lateral

b) left-lateral

3. Oblique slip

Seismic Waves

• Caused by a release of energy from rupture of

a fault

• Body waves: travel through the body of the Earth:

• P waves, primary or compressional

waves

– Move fast with a push/pull motion

– Can move through solid, liquid, and gas

• S waves, secondary or shear waves

– Move slower with an up/down motion

– Can travel only through solids

Seismic Waves, cont.

Surface waves: move along

Earth’s

surface

• P and S waves that reach the

surface

• Travel more slowly than body

waves

• Complex horizontal and vertical

ground

movement

Rayleigh Waves
• Rolling motion

• Responsible for most of the

damage near epicenter

Shaking

produces both

vertical and horizontal

movement

Seismic Waves, cont.

Surface waves: move
along Earth’s surface

• P and S waves that reach the
surface

• Travel more slowly than body
waves

• Complex horizontal and
vertical ground movement

Love Waves
• Horizontal ground

shaking

• Faster than Rayleigh
waves

• Do not move through water
or air

• Very hazardous!

Wave direction

Calculating Epicentral Distance

P wave has velocity VP ; S wave have velocity

VS

VS <

VP

Both originate at the same place – the hypocenter – and travel the same distance, but

the S wave takes longer to arrive than the P wave.

Time for S wave to travel a distance D:

Time for P wave to travel a distance D:

The time difference between them is:

Now solve for the distance D:

Time =
Distance

Velocity

TS =
D

VS

TP =
D

VP

(TS -TP ) =
D

VS

D

VP
= D

1

VS

1
VP

æ

è
ç

ö

ø
÷=D

VP -VS

VPVS

æ
è
ç
ö

ø
÷

𝐷 =
𝑉𝑃𝑉𝑆
𝑉𝑃 − 𝑉𝑆

𝑇𝑠 − 𝑇𝑝

Earthquake

Shaking

• Shaking experience depends on:

1. Earthquake magnitude

2. Location in relation to epicenter and direction of rupture

3. Local soil and rock conditions

• Strong shaking from a moderate magnitude or higher

Fault Rupture

• Slip: displacement
between two rock
blocks

• Rupture area: surface
where rocks have
moved

• Both parameters used
in advanced magnitude
calculations because
related to the energy
needed to move large
blocks of rock

Earthquake

Magnitude

Richter scale
• Not typically used anymore

• Recorded with a seismograph

– Measures maximum amount of ground shaking due to S wave

• Local magnitude

– Depends on where it is located

– Specific to only one location

• For events with shallow hypocenters that are located less than 500
km from seismograph stations

• Based on idea that the bigger the earthquake, the greater the
shaking of the Earth

Is this always true though??
Photo credit: SSA

Richter Scale – Local earthquake magnitude (ML

)

• For local earthquakes in Calif.

• Recorded on Wood-Anderson.

• ML = log A(mm) + 3 log[R] – 2.92

• Reference :

• Should expect Amplitude of 1 mm

• At Distance of 100 km

• From ML=3

Use the above equation or the graphical
method

• Three vertical axis; R (or S-P), M, A

• Measure (S-P)

• Find R : R= 8(S-P)

• Mark R on R vertical axes

• Measure A, mark on axis

• Draw a line between two marks

• Obtain M

Example:

• Amplitude = 23 mm

• S-P time = 24 s

• Thus Ml=5

Earthquake Magnitude

• Richter scale
– Not typically used anymore

– Recorded with a seismograph (or seismometer)
• Measures maximum amount of ground shaking due to S wave

– Local magnitude
• Depends on where it is located

• Specific to only one location

• Moment magnitude scale
– Absolute size of earthquake (compare multiple locations)

– Measurement of actual energy released
• Determined from area of rupture, amount of slippage, and the rigidity of

the rocks

– Estimates can take days to calculate

Seismic Moment

• Current method of measuring earthquake size

• Relies on the amount of movement along the fault that

generated the

earthquake

Where A is the fault area (W x L), μ is the shear modulus

(rigidity) and D is the amount of slip

Units of

or
[N ×m]

[dyne ×cm]

M0 = mAD

Total Slip in the M7.3 Landers Earthquake

Rupture on a Fault

Moment Magnitude

• Magnitude scale that uses the seismic moment of an

earthquake

• More accurate for large earthquakes since it is tied to the

physical parameters of the fault such as rupture area, slip

and energy release

• Measures amount of energy released by the movement

along the whole rupture surface

MW =
2

3
log(M0 )-6.1 No units!

Global Frequency of Earthquakes

Descriptor Average Magnitude Annual Number of Events

Great 8 and higher 1

Major 7–7.9 14

Strong 6–6.9 146

Moderate 5–5.9 1344

Light 4–4.9 13,000 (estimated)

Minor 3–3.9 130,000 (estimated)

Very Minor 2–2.9
1,300,000 (estimated)

(approx. 150 per hour)

Source: U.S. Geological Survey, “Earthquake Statistics,” 2000–2015, available at

https://earthquake.usgs.gov/earthquakes/browse/stats.php. Accessed 7/21/2017.

Ground motion and energy comparison

• Magnitude is on a logarithmic scale

• When magnitude increases by 1, the ground motion

(amount of shaking) increases 10 times

– A M6 earthquake has 10 times larger ground motion than a M5

– A M6 has 100 times more than a M4

• Energy is different

– When magnitude increases by 1, amount of energy released

increases ~32 times

Relationship between physical fault

characteristics and Mw?

Magnitude versus Fault Length

10

100

1000

10000

6 7 8 9 10

Magnitude

F
a

u
lt

L
e

n
g

th
(

k
m

)

Magnitude of earthquake is controlled by

fault length

(or area) that ruptures

Magnitude versus

fault length

(determined from

aftershock zone

length) for various

earthquakes (Alaska,

1964; Denali, 2002;

Landers, 1992; Loma

Prieta, 1989;

Northridge, 1994,

etc.). Results were obtained
using Seismic/Eruption views.

Alaska, 1964

Denali, 2002

Landers, 1992

Sumatra, 2004

Magnitude versus fault length

Northridge, 1994

Loma Prieta, 1989

Equivalent Mw of a

variety of seismic

events, human-

made events, and

other phenomena

Earthquake

Intensity

• Measured by Modified Mercalli Scale
• Qualitative scale (I-XII) based on damage to structures and

people’s perceptions
• Can vary within an earthquake with a single magnitude

• Can vary from country to country

• Modified Mercalli Intensity Maps
• show where the damage is most severe

• Based on questionnaires sent to residents, newspaper articles, and
reports from assessment teams

• Recently, USGS has used the internet to help gather data more quickly

Abbreviated Modified Mercalli Intensity Scale

Maps of Intensity
Shake Maps use high-quality seismograph data to show areas of intense shaking

Useful in crucial minutes after an earthquake

– Show emergency personnel where greatest damage likely occurred

– Locate areas of possible damaged gas lines and other utilities

1994 M6.7 Northridge earthquake 2001 M6.8 Nisqually earthquake

1994 Northridge
2001 Nisqually

Magnitude

is a measure for the size or energy release

of an earthquake

Intensity

is a measure for the degree of shaking

Factors Affecting Intensity

An earthquake has only one magnitude.

The same magnitude earthquake can
have different effects in different areas.

Why??

Intensity at a given location depends on:

– Earthquake magnitude

– Epicenter location

– Distance from epicenter

– Hypocenter depth

– Direction of rupture

– Duration of shaking

– Local soil conditions

– Building style

Depth of Focus

• Focus is the place
within the Earth where
the earthquake starts

• Depth of earthquake
influences the amount
of shaking
• Deeper earthquakes

cause less shaking at the
surface

• Lose much of the energy
before reaching surface
• Loss of energy is called

attenuation

Direction of Rupture

• Direction that the

rupture moves along

the fault influences the

shaking

• Path of greatest

rupture can intensify

shaking

• Directivity contributes

to amplification of

seismic waves

Direction of

Rupture

toward the

Area of Most

Intense

Shaking

Local Geologic Conditions

• Nature of the ground materials affects the earthquake
energy

• Different materials respond differently to an earthquake

• Depends on their degree of consolidation
– Seismic waves move faster through consolidated bedrock

– Move slower through unconsolidated sediment

– Move slowest through unconsolidated materials with high water
content

• Material amplification
– Energy is transferred to the vertical motion of the surface waves

Material

Amplification

of Shaking

Material

Amplification of

Shaking

El Salvador, 2001L’Aquila, 2009

Pakistan, 2005 China, 2008

Ground Motion During Earthquakes

• Buildings are designed to handle vertical forces (weight

of building and contents)

>>> vertical shaking in earthquakes is usually safe

• Horizontal shaking during earthquakes

>>> can do massive damage to

buildings

• Acceleration

– Measured as acceleration due to gravity (g)

– Weak buildings can be damaged by as little as 0.1g

– At isolated locations, peak ground acceleration can be

as much as 1.8g (Tarzana Hills in 1994 Northridge, CA)

Periods of Buildings and Responses of Foundations:

• Buildings have natural frequencies and periods

• Periods of swaying are about 0.1 second per story

– 1-story house shakes at about 0.1 second per cycle

– 30-story building sways at about 3 seconds per cycle

• Building materials affect building periods

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

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

• Velocity of seismic wave depends on material through

which it is moving

– Faster through hard rocks/materials

– Slower through soft rocks/materials

Ground Motion During Earthquakes

Geographic Regions at Risk from Earthquakes

• Earthquakes not randomly distributed

• Most along plate boundaries

Geographic Regions at Risk from Earthquakes
• Earthquakes not randomly distributed
• Most along plate boundaries

Plate tectonics and

earthquakes

Exists relation between tectonic environment, deformation

forces and earthquake characteristics

Divergent Zone

• Dominant
deformation force:
tension

• Stress is released
in frequent, strong,
and shallow
earthquakes

• E.g., East Pacific
Rise (MOR), East
African Rift System
(no oceanic litho
yet!)

Tension

Plate Boundary Earthquakes

• Subduction Zones

– Site of the largest earthquakes

– Megathrust earthquakes

– Example: Cascade Mountains

– Convergence between a continental and oceanic

plate

– Example: Aleutian Islands

– Convergence between two oceanic plates

• Transform Fault Boundaries

– Example: San Andreas Fault in

California

, Loma Prieta

earthquake

– Boundary between North American and Pacific plates

Earthquakes at Convergent Zones

Convergent Zones

• Region where two tectonic plates collide

• Dominant deformation force – compression

– Infrequent and great earthquakes

– Immense amount of energy is stored, then suddenly released

– Shallow, intermediate and deep earthquakes

Megathrust

earthquakes due to

shear stress at the

contact between the

overriding and

subducting plates

2010 Chile Megathrust Earthquake

1960 M9.5 Chile

Earthquake –

largest known

Earthquake

1957
1964

1960

Magnitude 9+

2011

1700

All the M9.0 earthquakes are

along subduction zones!

All have generated tsunamis

Rupture surfaces for the Pacific Rim subduction zones

Potential areas for

M9.0 earthquakes.

Subduction zones

generate the really

large earthquakes.

Earthquakes in continent-

continent collisions

Active Faults in Tibet, China, Southeast Asia

What is the cause of all these faults?

Earthquakes along Transform Faults

• Dominant deformation force: shear

• Stress released in infrequent, major and shallow

earthquakes

• San Andreas fault, CA

– Transform fault accommodating horizontal movement

between the Pacific and North American plates

– NO material created nor consumed

– Fault created as a result of the subduction of the

Farallon plate under the North American plate in the last

30 Ma

20 Ma 10 Ma

Earthquakes along Transform Faults

Earthquakes and

hot spots

• Dominant deformation

forces: tension

(mainly) and shallow

earthquakes

• Frequent, strong and

shallow earthquakes

Earthquakes occur at shallow

depth due to magma movement

beneath the volcano

Hot spots and earthquakes

Hypocenters beneath

Kilauea volcano, Hawaii

When magma is on the

move at shallow depths,

it can generate a nearly

continuous swarm of

relatively small near-

surface earthquakes

Intraplate Earthquakes

• Earthquakes that occur within plates

• Example: New Madrid seismic zone

• Located near St. Louis, MO

• Historic earthquakes similar in magnitude

to West Coast quakes

• Often smaller M than plate boundary

quakes, but

• Can cause considerable damage due to

lack of preparedness

• Can travel greater distances through

stronger continental rocks

Plate Boundary vs. Intraplate Earthquakes

Why the difference in shaking areas?

Intraplate Earthquakes of Eastern Canada

Ancient St.

Lawrence River Rift

and its two failed

arms

Earthquake Effects

• Primary – caused directly by fault movement

• Ground shaking

• Surface rupture

• Secondary

• Liquefaction of ground

• Regional changes in land elevation

Landslides

• Fire

Tsunamis

• Disease

Shaking and Ground Rupture

• Ground rupture

– Displacement along the fault causes cracks in surface

• Fault scarp

• Shaking

– Causes damage to buildings, bridges, dams, tunnels,

pipelines, etc.

– Measured as ground acceleration

– Buildings may be damaged due to resonance

• Matching of vibrational frequencies between ground and building

Site Amplification

Liquefaction

• A near-surface layer of water-saturated sand changes
rapidly from a solid to a liquid

• Causes buildings to “float” in earth

• Common in M 5.5 earthquakes in younger sediments

• After shaking stops, ground re-compacts and becomes
solid

Liquefaction, cont.

Regional Changes in Land Elevation

• Vertical deformation linked to some large earthquakes

• Regional uplift

• Subsidence

• Can cause substantial damage on coasts and along streams

• Can raise or lower

the ground-water table

http://www.nzgs.org/library/uc-geologists-key-

contributors-to-fault-rupture-mapping-following-

the-m7-8-kaikoura-earthquake/

http://www.nzgs.org/library/uc-geologists-key-contributors-to-fault-rupture-mapping-following-the-m7-8-kaikoura-earthquake/

Landslides

• Most closely linked natural
hazard with earthquakes

• Earthquakes are the most
common triggers in
mountainous areas

• Can cause a great loss of
human life

• Can also block rivers creating
“earthquake lakes”

2002 Nov 3: Denali M 7.9 earthquake

Caused landslides in mountains (unpopulated areas)

Mosaic view of rock avalanches across Black Rapids Glacier.

Photo by Dennis Trabant, USGS; mosaic by Rod March, USGS

2002 Nov 3: Denali Mw7.9 earthquake

2002 Nov 3: Denali Mw7.9 earthquake

Fires
• Shaking and surface displacements

• Cause power and gas lines to break and ignite

• Knock over appliances, such as gas water heaters, and leaks ignite

• Threat even greater due to

• Damaged firefighting equipment

• Blocked streets and bridges

• Broken essential water mains

Tsunamis

• Long wavelength sea waves (160km)

• 800 km/hr (500 mi/hr)

• Long wave periods [160km/(800km/hr)] =12 min.

• Generated by

– Earthquake displacement of seafloor

– Submarine mass slides

– Explosive volcanic eruptions

– Impacts

2004 Sumatra

Earthquake

and Tsunami

Disease

• Causes:
– Loss of sanitation and housing

– Contaminated water supplies

– Disruption of public health services

– Disturbance of the natural environment

– Rupture of sewer and water lines
• Water polluted

Groundwater and Energy Resources

• Geologic faults from earthquakes greatly influence
underground flow of:
– Water

– Oil

– Natural gas

• Fault zones can act as preferential paths

• Can create natural and underground dams
– Slow or redirect flow

– Oases in some arid areas

– Accumulation of oil and gas

Mineral Resources

• Faulting may be responsible for accumulation or

exposure of economically valuable minerals

• Mineral deposits develop along fault cracks called

veins

– Can be the source of precious metals

– Those on large fault zones may produce enough to be

economically viable for extraction

Earthquakes Caused by Human Activity

• Loading Earth’s crust, as in building a dam and
reservoir
– The weight from water reservoirs may create new faults or

lubricate old ones

• Injecting liquid waste deep into the ground through
disposal wells
– Liquid waste disposals deep in the earth can create pressure

on faults

• Creating underground nuclear explosions
– Nuclear explosions can cause the release of stress along

existing faults

Induced Seismicity?

• Earthquake activity

that occurs above the

rate of naturally

occurring seismicity

due to human activity

• Injection of large

volumes of water at

high pressures ➔

hydraulic fracking

Future Earthquake Hazard Reduction

• Frequent small earthquakes

– May help prevent larger ones

– Release pent-up energy

– Reduction of elastic strain

• Scientists try to identify areas that have not

experienced earthquakes in a long time

– Greatest potential for producing large earthquakes

Minimizing the Earthquake Hazard

• Earthquakes strike without warning

– Great deal of research devoted to anticipating earthquakes

– Focus of minimization is on forecasting and warning

• Forecasts assist planners

– Considering seismic safety measures

– People deciding where to live

• Long-term forecasts

– Do not help anticipate and prepare for a specific earthquake

– Need predictions, but not there yet

The National Earthquake

Hazard

Reduction Program

• Major goals

– Develop an understanding of the earthquake source

• Obtaining information about the physical properties and mechanical

behavior of faults

• Develop models of the physics of the earthquake process

– Determine earthquake potential

• Detailed study of active regions, determine rates of deformation

• Calculate probabilistic forecasts

– Predict effects of earthquakes

• Obtain information to predict ground rupture and shaking and effects on

structures

• Apply research results

The Canadian National Seismograph Network

Seismic Risk

RISK = VULNERABILITY x HAZARD

Where is vulnerability especially high?

How to determine seismic hazard?

1. Where in the past have we felt significant earthquakes?

2. Are there any geographic patterns? Magnitude repeats?

3. Which areas are most vulnerable?

Seismic Risk

RISK = VULNERABILITY x HAZARD
Where is vulnerability especially high?
How to determine seismic hazard?

What

patterns

do you

see?

Seismic Risk

National Building Code of Canada (NBCC)

Seismic guidelines used to design and construct buildings that are as

earthquake-resistant as necessary for the expected seismic hazard of their

setting

Classification based on velocity of shear waves in the top 30 m of material

Estimation of

Seismic Risk

• Hazard maps show
earthquake risk

• Probability of a
particular event or the
amount of shaking

• Damage potential
determined by how
the ground moves and
how the buildings
within the affected
region are constructed

http://earthquakescanada.nrcan.gc.ca/hazard-alea/simphaz-en.php

Estimation

of Seismic

Risk in

California

Earthquake Prediction

• The when and where of

a future earthquake

• Not currently possible

with our knowledge of

faults and stress

• Would require:

• The current stress stage of

a fault

• The maximum strength of

a fault

• The stress stage after an

earthquake

Earthquake Forecasting

• The likelihood of

earthquakes happening in

a specified area over a

specified period

• Can be determined from:

• Known faults

• Historical earthquakes

• Seismicity maps

• Paleoseismology from

trenches

• Geodetic strain rates from

GPS – crustal motion maps

Short-Term Prediction

• Pattern and frequency of earthquakes

– Foreshocks

• Deformation of ground surface

– Changes in land elevation

Seismic gap

s along faults

– Areas that have not seen recent quakes

• Geophysical and Geochemical changes

– Changes in Earth’s magnetic field, groundwater levels

Earthquake Warning Systems?

• Possible? Technically yes…

could develop system that

would provide up to 1

minute of warning
• Network of seismometers and

transmitters along the San

Andreas Fault

• Earthquake warning system

NOT a prediction tool –

earthquake has already

happened

• Concern for liability issues
• False alarms

• Failures

Community Adjustments to the Earthquake Hazard

• Location of critical facilities
– Should be located in earthquake safe locations

– Need detailed maps of ground response (microzonation)

• Structural protection
– Buildings must be designed and/or retrofitted to withstand

vibrations

– “Earthquakes don’t kill people, buildings kill people”

• Education
– Could include pamphlets, workshops, information on internet

– Earthquake and tsunami drills

• Increased insurance and relief measures
– Vital to help recovery from an earthquake

Earthquake Hazard Model Design

Earthquake
Hazard

Model

Design

example

2011 Tohoku Earthquake

• M 7.2 earthquake detected two days before
– This was a size that was predicted to happen any day

– Did not expect it to be a foreshock to a larger earthquake

• Pacific plate slid under the Eurasian plate
– Earthquake 500 times more powerful than history suggested

– Also produced larger than predicted tsunami

• Automatic alert went out 8 seconds after P waves
confirmed
– Allowed 10 seconds of preparation

2011 Tohoku

Earthquake, cont.

• Few buildings
collapsed
• Allowed occupants to

escape

• However, widespread
superficial damage and
minor structural damage

• Most damage due to
tsunami damage,
liquefaction, and
landslides

• M 9.0 earthquake
triggered a tsunami that
was up to 120 m

• Fukushima nuclear
disaster

Japan
The most seismically active

country in the world. 2 or 3 large

earthquakes per century

Up to 5 M8 earthquakes per

century!

http://www.esri.com
http://prezi.com

Mexico City, 1985

• Mw 8.3 megathrust earthquake broke ~350 km away from

Mexico City

• ~10,000 people died

• What caused this

earthquake?

• Michoacan

Seismic gap

North

American

plate

Cocos plate

Why so much shaking

here??

Observations – Mexico City, 1985

• Very strong motions produced 400 km from the fault rupture due to the

response of soft clays (i.e. near-surface geology)

• Motion and damage should have been minimal because of distance

from source

Resonance!

• Amplification of

surface waves

due to sediment

filled basin

• Specific

resonance of

medium-height

buildings

• Weak structures

Most severe damage to almost

400 buildings of between 7 and

18 storeys in height. (EEFIT,

1986)

Chapter 3 Summary

• Earthquakes are common along tectonic plate boundaries

where faulting is common.

• Faults are fractures where rocks on one side of the

fracture have been offset with respect to rocks on the

other side.

• Displacement is caused by compressional, tensional, or

shearing stresses and can be mainly horizontal or mainly

vertical.

Chapter 3 Summary, cont.

• A fault is usually considered active if it has moved during

the past 10,000 years and potentially active if it has moved

during the past 2 million years.

• Before an earthquake, elastic strain builds up in the rocks

on either side of a fault as the sides pull in different

directions.

• Released elastic strain energy radiates outward in all

directions from the ruptured surface of the fault in the form

of seismic waves.

Chapter 3 Summary, cont.

• Seismic waves are vibrations that compress (P) or shear

(S) the body of Earth or travel across the ground as

surface waves.

• Some faults exhibit tectonic creep, a slow displacement

not accompanied by felt earthquakes.

• Large earthquakes release a tremendous amount of

energy measured on a magnitude (M) scale.

Chapter 3 Summary, cont.

• Earthquake intensity varies with the severity of shaking

and is affected by proximity to the epicenter, the local

geological environment, and the engineering of structures.

• Buildings highly subject to damage are those that (1) are

constructed on unconsolidated sediment, artificially filled

land, or water-saturated sediment, all of which tend to

amplify shaking; (2) are not designed to withstand

significant horizontal acceleration of the ground; or (3)

have natural vibrational frequencies that match the

frequencies of the seismic waves.

Chapter 3 Summary, cont.

• Most earthquakes occur on faults near tectonic plate

boundaries.

• Intraplate earthquakes are also common various parts of

the United States.

• Some of the largest historic earthquakes in North America

occurred within the plate in the central Mississippi Valley in

the early 1800s.

Chapter 3 Summary, cont.

• The primary effect of an earthquake is violent ground

motion accompanied by fracturing, which may shear or

collapse large buildings, bridges, dams, tunnels, pipelines,

levees, and other structures.

• Other effects include liquefaction, regional subsidence,

uplift of the land, landslides, fires, tsunamis, and disease.

• Natural service functions include enhancing groundwater

and energy resources and exposing or contributing to

formation of valuable mineral deposits.

Chapter 3 Summary, cont.

• Human activity has locally increased earthquake activity

by fracturing rock and increasing water pressure

underground below large reservoirs, by deep-well disposal

of liquid waste, and by setting of underground nuclear

explosions.

• Understanding how we have caused earthquakes may

eventually help us control or stop large natural

earthquakes.

Chapter 3 Summary, cont.

• Reducing earthquake hazards requires detailed mapping

of geologic faults, the cutting of trenches to determine

earthquake frequency, and detailed mapping and analysis

of earth materials sensitive to shaking.

• Adjustments to earthquake hazards include improving

structural design to better withstand shaking, retrofitting

existing structures, microzonation of areas of seismic risk,

and updating and enforcing building codes.

Chapter 3 Summary, cont.

• To date, scientists have been able to make long- and

intermediate-term forecasts for earthquakes using

probabilistic methods but not consistent, accurate short-

term predictions.

• Early warning systems have been shown to be effective in

Japan, but no such system exists in the United States or

Canada.

• Warning systems and earthquakes prevention are not yet

reliable alternatives to earthquake preparedness.

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