ESC1000 • Earth Science • Summer 2016
Plate Tectonics
and
Earthquakes
(Chapters 4 & 5)
1
What’s happening here, and
how are these images related to plate tectonics?
Your questions….
Course Logistics
• Sign-in / sign-out sheets and syllabus contract– Make sure you sign them.
• Exam 1 moved to next Wednesday, July 6
(I will make other changes to our schedule shortly)– 25 multiple-choice and true-false questions
– Most of the material will be from Chapters 1, 4, and 5.
– I will ask you to interpret figures from Chapters 2 and 3.
– I will also give you one page of major definitions and processes to use as
reference on the exam. My goal is to post these on the website around
Friday.
– Work through the study guide!
(We can do some of this today, if we have time.)
• Extra credit now posted.– Three opportunities, three due dates.
2
Chapter 4: Plate Tectonics
1. Continental Drift
2. Evidence from the
Seafloor
3. Plate Tectonics
4. Plate Boundaries
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
3
4
Plate Tectonics: Learning Goals• What are the layers of the Earth?
• Crust: includes continental and oceanic crust (how do they differ)?
• Mantle: includes lithosphere and asthenosphere
• Outer core
• Inner core
5
Plate Tectonics: Learning Goals• What are the layers of the Earth?
• Crust: includes continental and oceanic crust (how do they differ)?
• Mantle: includes lithosphere and asthenosphere
• Outer core
• Inner core
• Know at least five different observations that supported the theory of
continental drift and (later) the theory of plate tectonics. Examples:
• Shape of the continents
• Evidence of past climates (fossils, glaciation)
• Mountain structure and composition
• Distribution of earthquakes, volcanoes, heat
• Seafloor spreading evidence: topography, age of seafloor, magnetism
6
Plate Tectonics: Learning Goals• What are the layers of the Earth?
• Crust: includes continental and oceanic crust (how do they differ)?
• Mantle: includes lithosphere and asthenosphere
• Outer core
• Inner core
• Know at least five different observations that supported the theory of
continental drift and (later) the theory of plate tectonics. Examples:
• Shape of the continents
• Evidence of past climates (fossils, glaciation)
• Mountain structure and composition
• Distribution of earthquakes, volcanoes, heat
• Seafloor spreading evidence: topography, age of seafloor, magnetism
• What are the three types of plate boundaries?
• How are they similar or different from each other?
• Where on Earth would you find them?
Our Solar System
The Good Earth, Chapter 2: Earth in
Space
Terrestrial Planets
• Composed of rocks
• Divided into compositional
layers
− Crust – composed of lighter
elements (e.g., silicon, oxygen)
− Mantle
− Core – composed of heavier
elements (e.g., iron, nickel) found
in metallic meteorites
− Outer core: liquid
− Inner core: solid7
Earth Structure
The Good Earth/Chapter 4: Plate Tectonics
Earth has 3
compositional
layers – crust,
mantle, core
The major
features on
Earth’s
surface are
the result of
processes in
the upper few
hundred
kilometers
8
Earth Structure
The Good Earth/Chapter 4: Plate Tectonics
• Lithosphere
− Rigid layer
composed of crust
& uppermost mantle
− Divided into mobile
tectonic plates
• Asthenosphere
− Weaker layer found
in upper part of
mantle
− Flows due to small
proportion (1%) of
melted minerals
Two key layers in crust and upper mantle
9
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
Which is the actual map of Earth’s features?
10
Continental Drift
The Good Earth/Chapter 4: Plate Tectonics
• Continental Drift: continents
have occupied different
locations on Earth’s surface
in the geologic past
− 250 million years ago the
continents were all together in a
“supercontinent”, Pangaea
− Continents “drifted” across
surface of Earth to their present
locations
Wegener’s Paradigm:
11
Matching features
• Distribution of plant and animal fossils matched
between continents
Wegener’s Observations:
Continental Drift
The Good Earth/Chapter 4: Plate Tectonics
12
Matching features
• A continuous
mountain belt can
be formed when
Pangaea is
reassembled
Wegener’s Observations:
Continental Drift
The Good Earth/Chapter 4: Plate Tectonics
13
Matching features
• Opposing edges of
continents fit together
along the shallow
continental shelf
• Unusual rock
sequences match
between Africa and
South America
Continental Drift
Wegener’s Observations:
The Good Earth/Chapter 4: Plate Tectonics
14
Paleoclimates
• Evidence of a thick
ice sheet throughout
the southern
continents
• Rocks formed in
tropical conditions
(e.g., coal swamps)
in North America near
(paleo)equator
Continental Drift
Wegener’s Observations:
The Good Earth/Chapter 4: Plate Tectonics
15
Continental Drift
The Good Earth/Chapter 4: Plate Tectonics
Wegener’s Continental Drift hypothesis
was not widely accepted because:
1. Wegener was considered an “outsider” among
geologists, and his use of deductive reasoning
was considered unusual for the time
2. Wegener could not explain how the continents
moved
16
Plate Tectonics Concept Survey
The Good Earth/Chapter 4: Plate Tectonics
How is fixing this plate analogous to
Wegener’s methods of assembling the
continents into Pangaea?
17
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
Which of the lines of evidence were not
used to support Wegener’s continental
drift hypothesis?
A. The distribution of fossils.
B. Fit of continents.
C. Match of mountain belts.
D. Earthquake locations.
E. Paleoclimate data.
18
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
Which of the lines of evidence were not
used to support Wegener’s continental
drift hypothesis?
A. The distribution of fossils.
B. Fit of continents.
C. Match of mountain belts.
D. Earthquake locations.
E. Paleoclimate data.
19
Going from Observations to Hypothesis
The Good Earth/Chapter 4: Plate Tectonics
1. Seafloor topography
2. Age of the seafloor
3. Heat flow
4. Volcanoes
5. Earthquakes
6. Magnetic field
In the decades following Wegener’s research,
key observations about the seafloor contributed
to a new understanding of Earth processes
In-Class Activity 2 Part A:
In groups, analyze two of these observations
to make a drawing of the Earth’s plates. 20
Three Types of Plate Boundaries
The Good Earth/Chapter 4: Plate Tectonics
Divergent • plates move apart
Convergent • plates move
toward each other
Transform• plates slide past
each other
In-Class Activity 2 Part A, continued:
On your drawing, label one example of each of
the three types of plate boundaries.
21
• http://highered.mheducation.com/sites/0073524107/student_view0/
chapter4/how_seafloor_spreading_creates_magnetic_polarity_strip
es.html
• http://highered.mheducation.com/sites/0073524107/student_view0/
chapter4/magnetic_reversals_at_mo_ridge.html
22
Some Information to Get You Started:
6. Magnetic Field:
• https://www.youtube.com/watch?v=D69hGvCsWgA
1. Seafloor Topography:
1. Seafloor Topography
The Good Earth/Chapter 4: Plate Tectonics
Seafloor Topography
• Oceanic ridge
− Submarine mountain
range that is a source
of volcanic activity
− May reach surface
(Iceland)
• Oceanic trench
− Narrow, deepest
portion of ocean floor
(Puerto Rico trench)
23
1. Seafloor Topography
The Good Earth/Chapter 4: Plate Tectonics
• Continental shelf
− Narrow, shallow
ocean surrounding
continents
• Abyssal plain
− Relatively level
seafloor, often with
volcanoes (Bermuda)
24
1. Seafloor Topography
The Good Earth/Chapter 4: Plate Tectonics
• Oceanic ridges (underwater mountains)
− Oceanic ridge system occupies much of the seafloor
in all the world’s ocean basins
− Often found toward center of oceans
25
1. Seafloor Topography
The Good Earth/Chapter 4: Plate Tectonics
• Oceanic trenches
− Found adjacent to some continents or island chains
and along the margins of oceans
− Most common around Pacific Ocean
26
2. Age of the Ocean Floor
The Good Earth/Chapter 4: Plate Tectonics
• Age of seafloor rocks
varies systematically
• Rocks of the seafloor
are young compared
to most rocks on the
continents
− Rocks on ocean floor
are younger than 200
million years old
− Rocks on continents
are as old as 4,000
million years
27
2. Age of the Ocean Floor
Age of the Ocean Floor
1. Youngest rocks located near the centers of ocean basins
2. Older rocks along margins of ocean basins
3. Age of seafloor rocks
increases symmetrically from
near centers of oceans
The Good Earth/Chapter 4: Plate Tectonics
28
3. Heat Flow
The Good Earth/Chapter 4: Plate Tectonics
hottercooler
• Heat flow varies
systematically
around the
world
− Highest along
oceanic ridges
− Lowest on
continents and
in ocean far
from ridges
29
4. Volcanoes
The Good Earth/Chapter 4: Plate Tectonics
• Most active
volcanoes are
located around
the Pacific rim
(Ring of Fire)
− Found near
oceanic
trenches
Global distribution of active volcanoes
Ring of fire
30
4. Volcanoes (and 1. Seafloor Topography)
The Good Earth/Chapter 4: Plate Tectonics
• Most active
volcanoes
are found
near oceanic
trenches
31
5. Earthquakes
The Good Earth/Chapter 4: Plate Tectonics
• Earthquakes found
near oceanic ridges
and trenches
− Earthquakes
recorded to 800 km
depth
− Deep earthquakes
found only near
oceanic trenches
− Largest
earthquakes near
trenches Global distribution of earthquakes, 2005
32
5. Earthquakes (and 4. Volcanoes)
The Good Earth/Chapter 4: Plate Tectonics
• Earthquakes
become deeper
with distance from
trenches
− Define Wadati-
Benioff zones that
slope away from
ocean
− Often occur in
association with
volcanoesDeeper
earthquakes
Shallow
earthquakes
33
6. Magnetic Field
The Good Earth/Chapter 4: Plate Tectonics
• Earth’s magnetic
field has negative
and positive poles
located near the
North and South
poles
• A compass needle
lines up along lines
of magnetic force
(also called
magnetic flux)
34
6. Magnetic Field
The Good Earth/Chapter 4: Plate Tectonics
• Atoms in magnetic
minerals aligned parallel
to the magnetic field when
magma cooled to form
seafloor rocks
− Preserves ancient
magnetic field -
paleomagnetism
− Analysis reveals the
inclination of the field
where they formed – a
proxy for latitude
35
6. Magnetic Field
The Good Earth/Chapter 4: Plate Tectonics
− Each period of normal or
reversed polarity averages
250,000 years
− Longest = 10’s of millions
of years
− Shortest = 10’s of
thousands of years
− Few thousand years to
change polarity (normal
reverse or reverse
normal)
Magnetic Field Reversals
−Normal polarity when negative
magnetic pole is near geographic
North Pole (current status)
36
6. Magnetic Field
Paleomagnetism & Seafloor Spreading
The Good Earth/Chapter 4: Plate Tectonics
• Normal polarity rocks
currently forming from
magma along oceanic
ridge
− Marine surveys
measure strength of
Earth’s magnetic field
− Strength higher in
regions of normal
polarity, lower where
there is reverse
polarity
37
Plate Boundaries - Background
The Good Earth/Chapter 4: Plate Tectonics
Three types of plate boundaries
Divergent • plates move
apart
Convergent • plates move
toward each
other
Transform• plates slide past
each other
38
Plate Boundaries
Divergent
Transform
Convergent
Three types of plate boundaries
The Good Earth/Chapter 4: Plate Tectonics
39
Plate Boundaries
Divergent
Transform
Convergent
Three types of plate boundaries
The Good Earth/Chapter 4: Plate Tectonics
40
Plate Boundaries
The Good Earth/Chapter 4: Plate Tectonics
Convergent Boundary: 1. Ocean/Ocean
• When 2 oceanic plates collide, the older
lithosphere is consumed in the subduction zone
− Volcanic island
arc forms behind
trench on over-
riding plate
− Arc-trench gap
depends on angle
of subduction
zone
− Steeper slope =
smaller gap41
Plate Boundaries
The Good Earth/Chapter 4: Plate Tectonics
Convergent Boundary: 2. Ocean/Continent
• When an oceanic plate collides with a continental
plate, the oceanic plate is consumed in the
subduction zone
− Example: Nazca
plate descends
below western
South America
− Mountain ranges
form along active
margin
42
Plate Boundaries
The Good Earth/Chapter 4: Plate Tectonics
Convergent Boundary: 3. Continent/Continent
• Thickening of continental crust forms tallest
mountain ranges− Example:
Himalayas
formed where
India collided with
Eurasia
− Only type of
convergent
boundary without
oceanic trench
− No current
volcanic activity
43
Plate Boundaries
The Good Earth/Chapter 4: Plate Tectonics
Convergent Boundary vs. Crustal Thickness
• Thickest crust
found along
convergent
boundaries
− Himalayas, 70 km
thick
− Andes, up to 60
km thick
− Most continental
interiors, 30-40
km thick
44
Plate Boundaries
The Good Earth/Chapter 4: Plate Tectonics
Transform Boundaries
• Link sections of ridge or trench systems
• Plates move in opposite directions
• No lithosphere created, no lithosphere destroyed
45
Plate Boundaries
The Good Earth/Chapter 4: Plate Tectonics
San Andreas Fault, CA
• Links oceanic ridge systems
in Gulf of California and Juan
de Fuca plate
− San Francisco and most of
U.S. on North American plate
− Western California, including
Los Angeles, on Pacific plate
− Moving north collide with
Alaska
46
Reports from Groups
47
Seafloor Spreading Hypothesis
The Good Earth/Chapter 4: Plate Tectonics
Oceanic ridges
– high heat flow,
young rocks,
elevated seafloor
Ocean
margins with
trench – older
seafloor,
volcanism and
earthquakes
Ocean margins
without trench –
older seafloor, no
volcanoes or
earthquakes
http://highered.mheducation.com/sites
/0073524107/student_view0/chapter4/
seafloor_spreading.html
Observations
48
The Good Earth/Chapter 4: Plate Tectonics
Oceanic ridges
• Magma rises
from mantle,
forms new
oceanic crust
• Expansion of
seafloor results in
high elevations
• Seafloor moves
away from ridge
(conveyer belt)
creating a gap for
new material
Seafloor Spreading Hypothesis
Interpretations
49
The Good Earth/Chapter 4: Plate Tectonics
Oceanic trench
• Older seafloor
descends into
mantle at active
margin
• Melting of rocks
forms magma,
volcanism
• Earthquakes
where old
seafloor
consumedPassive margin
• Continent/ocean
transition
Seafloor Spreading Hypothesis
Interpretations
50
Evidence from the Seafloor
The Good Earth/Chapter 4: Plate Tectonics
Additional observations about the magnetic
properties of seafloor rocks supported the
seafloor spreading hypothesis
Earth has a magnetic field because it has:
1. Molten rock in the outer core
2. Heat to generate currents in outer core
3. Rotation to mix the currents
51
Seafloor Spreading Hypothesis
The Good Earth/Chapter 4: Plate Tectonics
Polarity of seafloor alternates
between normal and reverse
on either side of oceanic ridge
Observations &
Interpretations
52
Plate Tectonics
The Good Earth/Chapter 4: Plate Tectonics
Interactions of plates
along their
boundaries accounts
for the formation of
new lithosphere,
earthquakes,
volcanoes, and the
gradual movement of
continents.
53
Plate Tectonics
The Good Earth/Chapter 4: Plate Tectonics
Formation of new lithosphere at oceanic ridges
• New oceanic
lithosphere is added
along edges of two
plates that move
away from ridge
54
Plate Tectonics
The Good Earth/Chapter 4: Plate Tectonics
Generation of earthquakes and volcanoes
• Older oceanic
lithosphere is
destroyed at
subduction zone to
balance formation
of new material
− Earthquakes ( )
occur from surface to
~800 km depth in
descending plate
Continental lithosphere is not consumed in
subduction zones. Continents can break up or
combine but total volume remains the same. 55
Plate Tectonics
The Good Earth/Chapter 4: Plate Tectonics
Generation of earthquakes and volcanoes
• Older oceanic
lithosphere
destroyed at
subduction zone
Most continental margins are not plate boundaries
(e.g., Atlantic coast of North America) = passive margins
56
Plate Tectonics
The Good Earth/Chapter 4: Plate Tectonics
Rigid lithosphere is divided
into mobile tectonic plates
8 Major Plates:
African
Antarctic
Eurasian
Indian-Australian
Nazca
North American
Pacific
South American
57
Plate Tectonics
The Good Earth/Chapter 4: Plate Tectonics
Most plates composed of both continental and oceanic lithosphere (e.g., Africa, South America)
Numerous smaller plates (e.g., Arabian, Caribbean, Cocos, Juan de Fuca, Philippine, Scotia)
Oceanic ridges and trenches represent most plate boundaries
58
Plate Tectonics
The Good Earth/Chapter 4: Plate Tectonics
Rate of Plate Movements
1. Kaua‘i formed 5,000,000 years ago
2. Kaua‘i has moved 600 km (600,000 meters) since its formation
3. Kaua‘i moved 600,000/5,000,000 meters per year = 0.12 m/yr = 12 cm/yr
Hawaiian islands
form over a hot spot
in Pacific Ocean
600 km
59
Plate Tectonics
The Good Earth/Chapter 4: Plate Tectonics
Rate of Plate Movements
Modern satellite measurements reveal that plates move at
rates of ~1-15 centimeters per year
Fastest rates -Pacific, Nazca plates
Slowest rates -Antarctic, North American plates
60
Plate Tectonics
The Good Earth/Chapter 4: Plate Tectonics
Directions of Plate Movements
Can you predict which plates will get larger and which will grow smaller over the next few millions of years?
Plates move away from oceanic ridges and toward oceanic
trenches (subduction zones).
61
In-Class Activity 2 Part B
The Good Earth/Chapter 4: Plate Tectonics
How many plates are in this image?
A. 1
B. 2
C. 3
D. 4
E. 5
62
In-Class Activity 2: Part C
The Good Earth/Chapter 4: Plate Tectonics
Review the map below and identify which pair of
locations is moving closer together as a result of
plate tectonics?
A. Bombay and Sydney C. New York and London
B. Hawaii and Tokyo D. Cape Town and Sydney
63
Questions to help you review
Chapter 4
64
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
Which of the images below best
approximates the relative distribution
of Earth’s core, mantle and crust?
a) b) c) d)
Big core,
thin crustSmall core,
thick crust
Big core,
thick crust
Small core,
thin crust
65
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
Which image best approximates the shape
of the ocean floor in the Atlantic Ocean?
66
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
A. Deeper regions of the ocean floor are younger
B. The Pacific Ocean is larger than the Atlantic Ocean
because it contains older oceanic floor
C. Oldest oceanic crust is only present near trenches
D. Youngest seafloor rocks occur near oceanic ridges
Which statement is TRUE about the
relationship between age and
topography of the ocean floor?
67
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
How many plates are in this image?
A. 3
B. 4
C. 5
D. 6
68
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
The continental crust at Y is moving toward the …
A. Southeast
B. Southwest
C. Northeast
D. Northwest
69
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
A. 20 centimeters to the west
B. 20 centimeters to the east
C. 200 centimeters to the west
D. 200 centimeters to the east
The island of Bermuda is a
former volcano on the floor
of the western Atlantic
Ocean. Approximately how
far and in what direction
would the island travel in
100 years?
70
Place the phrases is the most appropriate
location on the Venn diagram.1. Rocks on either side of boundary are typically
of different ages.
2. Example: Nazca and South American plate
boundary.
3. Associated with oceanic trenches.
4. Oceanic lithosphere may be present on both
sides of the plate boundary.
5. Only young ocean lithosphere present.
6. Plates move away from each other (divergent
boundary).
7. Plates move toward each other (convergent
boundary).
8. Often associated with volcanoes.
9. Magma rises to surface at or near the
boundary.
10. Causes continents to divide.
11. Causes continents to combine.
12. Mountains present where continental
lithosphere involved.
13. Chains of volcanic islands form (island arcs).
The Good Earth/Chapter 4: Plate Tectonics
71
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
Which of the locations on the map all represent
examples of convergent plate boundaries?
A.1, 6, 8
B.3, 4, 5
C.2, 7, 9
D.2, 5, 6
E.3, 7, 8
72
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
Which of the numbered locations best represents
a plate boundary configuration similar to “c”?
A.1, 7
B.3, 8
C.4, 5
D.6, 9
73
Plate Tectonics Conceptest
The Good Earth/Chapter 4: Plate Tectonics
Which location on the map represents an
example of a transform plate boundary?
A. 1
B. 3
C. 5
D. 6
E. 8
74
Chapter 5: Earthquakes
1. Experiencing an Earthquake Firsthand
2. The Science of Ghost Forests and Mega-earthquakes
3. Faults, Earthquakes, and Plate Tectonics
4. Seismic Waves and Earthquake Detection
5. Measurement of Earthquakes
6. Earthquake Hazards
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill
Education.
75
76
Earthquakes: Learning Goals(as questions)
• Where on Earth would you find earthquakes, and why?
• How do earthquakes differ, depending on the type of plate boundary?
• What is the difference between measuring earthquake magnitude and
earthquake intensity?
• What are some reasons why earthquakes cause more damage in some
locations, versus in other locations?
• What are the types of seismic waves, and how do they differ?
World Distribution of Earthquakes
The Good Earth/Chapter 5: Earthquakes
77
One major threat caused by earthquakes:
https://www.youtube.com/watch?v=Wx9vPv-T51I
Science and Society
Earth Scientist’s role in Society:
• Alert people to earth processes (hazards) that may cause damage or loss of life
• Provide for material needs of society by managing natural resources
• Protect us from activities that may endanger the natural environment
• Ensure the future of humanity from global threats such as climate change or an asteroid impact
The Good Earth, Chapter 1: Introduction to Earth
Science
78
The Good Earth, Chapter 1: Introduction to Earth
Science
Science and Society
Earth Scientist’s role in Society:
• Alert people to earth processes (hazards) that may cause damage or loss of life
• Prevention – Which hazards are we most likely (or least likely) to be able to prevent?
• Example: Prevention of flooding as a result of construction of floodwalls and levees
• Adjustment – strategies for minimizing the impact of hazards
• Example: Building code regulations in areas of frequent earthquakes
79
Experiencing an Earthquake Firsthand
The Good Earth/Chapter 5: Earthquakes
• More than 2 million
people killed by
earthquake hazards
in 20th Century
− 30 million US citizens
in earthquake hazard
zones
• Most deaths due to
building collapse
and tsunami
− Indian Ocean tsunami
claimed more than
230,000 lives
January 17, 1994 – Northridge, CA
• 57 killed, 9,000 injured
• $20 billion damage
estimate
Structures like this apartment
building were damaged by an
earthquake
80
The Science of Ghost Forests and Mega-Earthquakes
The Good Earth/Chapter 5: Earthquakes
• Stands of dead trees in
coastal marshes in
Washington state
− Similar to trees killed in
one of the largest
earthquakes ever
recorded (in Alaska)
• Were the Washington
trees a signal of a past
mega-earthquake?
− Radiocarbon data
indicated they died
between 1680 and 1720
− Was there a possible
earthquake source
nearby?Ghost forests in Alaska (top) and
along the coast of Washington. 81
The Science of Ghost Forests and Mega-Earthquakes
The Good Earth/Chapter 5: Earthquakes
• Mega-earthquakes
occur along
subduction zones
− Cascadia subduction
zone is approximate
size of rupture zone of
2004 Sumatra
earthquake (Indian
Ocean tsunami)
• A Cascadia
subduction zone
earthquake would
have generated a
substantial tsunami
− Where is the evidence
of a tsunami?
Location of the Cascadia subduction zone
relative to major cities of the Pacific
Northwest.82
The Science of Ghost Forests and Mega-Earthquakes
The Good Earth/Chapter 5: Earthquakes
• Tsunami-generated
sand deposits
discovered in coastal
marshes of Pacific
Northwest
− Similar to sand layers
formed by 1960 Chile
mega-earthquake and
2004 Sumatra earthquake
Tsunami sand deposits cover soil in Oregon
(top) and in Chile.
On the basis of historical records,
Japanese scientists hypothesized
that the Cascadia earthquake
occurred in January, 1700.
How did American scientists
test this hypothesis?83
The Science of Ghost Forests and Mega-Earthquakes
The Good Earth/Chapter 5: Earthquakes
• Tree ring analysis
revealed the ghost
forest trees died in
1700
− Pacific Northwest cities
are at risk from much
larger earthquakes
than was previously
thought
− Rare events, on
average 500 years
apart
− Stricter building codes
were established
Seattle, Washington
84
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
What do you observe in these images?
85
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
Hebgen Lake earthquake, Montana, 1959
This side moved down
• fault - a fracture in the crust on which
movement has occurred
fault scarp
This side moved down
fault scarp
86
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
Earthquake features. Only part of a fault
may move during an earthquake.
• Fault - a fracture in the
crust on which
movement has occurred
− A zone of weakness where
earthquakes occur
− Focus – location where
movement begins on fault
− Epicenter – location on
surface above the focus
− Fault scarp – “step” in
land surface formed by
movement on the fault
− Only part of a fault
typically breaks during an
earthquake 87
http://highered.mheducation.com/sites/0073524
107/student_view0/chapter5/earthquakes.html
Animation:
Earthquake Conceptest
An earthquake occurred on the Erie fault 5
kilometers beneath San Gabriel. Damage
from the earthquake was greatest in nearby
Fremont. The farthest report of shaking was
recorded in Stockton. Where was the
earthquake’s epicenter?
A. The Erie Fault
B. San Gabriel
C. Fremont
D. Stockton
The Good Earth/Chapter 5: Earthquakes
88
Earthquake Conceptest
An earthquake occurred on the Erie fault 5
kilometers beneath San Gabriel. Damage
from the earthquake was greatest in nearby
Fremont. The farthest report of shaking was
recorded in Stockton. Where was the
earthquake’s epicenter?
A. The Erie Fault
B. San Gabriel
C. Fremont
D. Stockton
The Good Earth/Chapter 5: Earthquakes
89
Types of Faults
The Good Earth/Chapter 5: Earthquakes
− strike-slip fault,
blocks on either
side of fault
move
horizontally, left
or right
Faults are classified by the relative movements
of rocks on either side of fault surface
− reverse fault,
block above an
inclined fault
moves up
− normal fault,
block above
an inclined
fault moves
down90
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
Rocks at land
surface offset to
form a fault scarp by
big 1964 Alaska
earthquake
Faults recognized by observing offset of features or
change in elevation of land surface
Fence offset 3
meters by San
Francisco
earthquake (1906)
Road damaged and
displaced by a fault
fault scarp
Horizontal fault movements
Vertical fault movement
91
In-Class Activity 2 Part D
The Good Earth/Chapter 5: Earthquakes
Earthquake features.
Only part of a fault may move during an
earthquake.
1. Research a specific earthquake.
(example: Sumatra, 2004)
2. Learn at least two characteristics
of this earthquake. This might
include:
- epicenter
- type of fault
- focal depth (etc)
3. Mark its location on your map.
4. What type of plate boundary is it
located on?
5. How did this earthquake differ from
earthquakes found at other plate
boundaries?
6. What were some factors that
influenced the level of damage? 92
http://highered.mheducation.com/sites/007
3524107/student_view0/chapter5/earthqua
kes.html
Earthquake Measurement: Magnitude
The Good Earth/Chapter 5: Earthquakes
Earthquakes described
as Minor to Great as
magnitude ranges
from 3 to more than 8
No maximum
value for
magnitude scale Largest measured earthquake
was Chile, 1960 – magnitude
9.5
Informal designation of
mega-earthquakes for events
of magnitude 9+
93
The Good Earth/Chapter 5: Earthquakes
• Magnitude is measured on
a logarithmic scale
− Each division represents a
10-fold increase in ground
motion
− Each division represents a
32-times increase in energy
released
Example: a magnitude 5
earthquake exhibits 100
times more shaking and
releases nearly 1,000 times
more energy
Earthquake Measurement: Magnitude
94
Earthquake Measurement: Intensity
The Good Earth/Chapter 5: Earthquakes
• Intensity is measured
using the Modified
Mercalli Scale
− 12-point scale using
Roman numerals
Intensity = Magnitude
I <3
II-III 3.0-3.9
IV-V 4.0-4.9
VI-VII 5.0-5.9
VIII+ 6+
Higher values depend on
ground materials, other
factors
95
The Good Earth/Chapter 5: Earthquakes
• Intensity is measured
using the Modified
Mercalli Scale
− Difficulties in
comparing earthquakes
from different regions
due to contrasts in
Population density
Building codes
Ground materials
Distance
Earthquake Measurement: Intensity
96
The Good Earth/Chapter 5: Earthquakes
• Intensity is measured
using the Modified
Mercalli Scale
− Useful for rapid collection
of online data following
earthquakes
− USGS generates
Community Internet
Intensity Maps (CIIMs)
Example: CIIM for 6.7
magnitude Northridge
earthquake (1994)
Note that damage is not
distributed uniformly with
distance from epicenter
Earthquake Measurement: Intensity
97
Extra slides you may wish to
use for reference in completing
Part D of In-Class Activity 2:
98
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
San Andreas fault, California, forms part of the
boundary between the North American and Pacific
plates
Stream channels
offset by recent
movements on
the fault
99
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
Fault movements are driven by
stresses produced by plate tectonics
Friction along the
fault surface is
enough to cause
most faults to “stick”.
All rocks are slightly
elastic. The build up
of stress causes the
rock to deform
(change shape).
After decades or
centuries, stress has
built up to sufficient
levels to overcome
friction and cause
fault movement100
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
• Recurrence interval –
time for build up of stress
to cause fault movement
and earthquake
− Longer recurrence intervals
(100s years) for biggest
earthquakes
− Decades or less for smaller
events
− Scientists can analyze the
build up of deformation
using instruments
− Creep meters
− Strain meters
− Satellites 101
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
• Seismic gap – segments
of active faults that have
not experienced recent
movements
− 1999 Izmit earthquake in
Turkey occurred in a
seismic gap
− Major faults break in
segments. Several
segments of the North
Anatolian fault broke
during previous years to
produce big earthquakes
− Fault is plate boundary
between Anatolian plate
and Eurasian plate102
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
World Distribution of Earthquakes
Most earthquakes
occur along plate
boundaries, relatively
few in interiors of
plates
Shallow earthquakes
much more common
than deep events
Divergent plate
boundaries (oceanic
ridges) characterized
by earthquakes with
shallow focal depths
(0-33 km)
103
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
World Distribution of Earthquakes
Largest earthquakes found
in association with
convergent plate
boundaries
Convergent plate boundaries (oceanic
trenches) characterized by
earthquakes with a range of focal
depths (0-800 km)
104
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
US Earthquakes
Largest, most frequent, US
earthquakes along convergent
plate boundary south of Alaska
Most US earthquake damage occurs
in populous California
− 62% chance of a large
earthquake in San Francisco Bay
area by 2032
105
Faults, Earthquakes, and Plate Tectonics
The Good Earth/Chapter 5: Earthquakes
Largest earthquakes found
in association with
convergent plate
boundaries Global distribution
of earthquakes,
2005
Global distribution
of earthquakes,
2004
How Consistent is
Earthquake
Activity?
106
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
• Strong (magnitude 6.7) Northridge
earthquake was the most recent to strike
developed area
− Hazards associated with earthquakes include
Ground Shaking
Aftershocks
Landslides
Elevation Changes
Liquefaction
Tsunami
107
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
Map of Northridge earthquake hazards
Buildings damaged
by shaking over a
wide area (red
dots)
epicenter
Shaking of >0.4 g
can collapse
freeway
overpasses
Landslides
108
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
• Ground shaking can be exaggerated by
weaker earth materials
− Less shaking for bedrock
− More shaking for soft mud, sand and gravel
Collapsed section of Cypress freeway following Loma Prieta earthquake, 1989
109
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
• Landslides common on
steep slopes when
shaken
− 11,000 landslides
associated with Northridge
earthquake
− 3 deaths associated with
inhalation of dust
containing fungal spores
110
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
− Mountains east of
Los Angeles raised
by 1 meter during
Northridge
earthquake
− Small islands near
Sumatra were
uplifted 1 to 3 meters,
exposing coral reefs
• Elevation changes
result from movement
on faults
These trees stumps from Sumatra were
originally on dry land. They were broken
off by the Indian Ocean tsunami and
dropped below sea level by fault
movement. 111
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
• Liquefaction occurs when water is released from
saturated earth materials that are violently shaken
− Material loses strength and collapses, causing subsidence
A car is partially swallowed by
liquefaction during an earthquake
(Christchurch, New Zealand, 2011)
Apartment buildings collapsed due to liquefaction
after 1964 Niigata (Japan) earthquake. 112
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
Tsunami
• Fault displacement of ocean floor displaces large volumes of water
− Often associated with subduction zones
− Fast moving, up to 960 km/hr
− Low waves in open ocean but can pile up 10s meters of water along coastline
113
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
How long did it take the Indian Ocean tsunami to reach:
India, 2 hrsAfrica, 7-11 hrs
S. America, 20+ hrsN. America, 29 hrs
Wave heights
up to 30
meters in
Sumatra
114
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
• Tsunami damage, northwestern Sumatra
Waves reached 31 m elevation
115
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
• Comparable wave heights interpreted to indicate mega-earthquakes of similar magnitude
− Variation in wave height related to differences along coast
Tsunami heights along coast of Japan for
Chile (1960) and Cascadia (1700)
earthquakes
116
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
• Multiple tsunami associated with a single earthquake (Chile, 1960)
− Approximately 10-30 minutes between wave crests
Water levels were both above (wave crest)
and below (wave trough) low tide level.
117
Earthquake Hazards
The Good Earth/Chapter 5: Earthquakes
• Sand deposits generated
by Indian Ocean tsunami
are similar to those
produced by tsunami
after 1700 Cascadia
earthquake
Tsunami
sand
deposits in
Sumatra
118
(if we have time)
Analyzing Earthquake Data
119
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
• Seismic waves –
vibrations caused
by an earthquake
− Travel in all
directions from the
focus
− Recorded on
seismograph
instrument
− A seismogram is the
printed record from
a seismograph
120
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
− Recorded on
seismograph
instrument
− A seismogram is the
printed record from a
seismograph
• Seismic waves –
vibrations caused by an
earthquake
− Travel in all directions
from the focus
Credit: U.S. Geological Survey; Department of the Interior/USGS
U.S. Geological Survey/photo by J.K. Nakata, U.S. Geological Survey
121
Seismograph Animation:
http://highered.mheducation.com/sites/00
73524107/student_view0/chapter5/seismo
meter_2.html
Types of Seismic Waves
The Good Earth/Chapter 5: Earthquakes
− Slower surface
waves travel
along Earth’s
surface
− Faster body
waves travel
through Earth’s
interior
P waves
S waves
122
http://highered.mheducation.com/sites/0073524107/
student_view0/chapter5/earthquake_waves.html
Earthquake Waves – Animation:
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
• 2 types of surface waves
− Rayleigh waves result in
vertical movement of
surface
− Love waves produce a
side-to-side movement
− Surface waves are
responsible for much of
earthquake damage
123
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
• 2 types of body
waves
− P (primary) waves
are the first to arrive
at a seismograph
station
4-6 km/s in crust
− Compress material
parallel to travel
direction
Slinky analogy
Animations124
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
• 2 types of body
waves
− S (secondary or
shear) waves arrive at
recording station
after P waves but
before surface waves
3-4 km/s in crust
− Vibrate material
perpendicular to
travel direction
Wave in rope
analogy
− Can not pass through
liquids (e.g., outer
core)125
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
• Time it takes seismic waves to reach a
seismograph station increases with distance
from the focus − Time interval
between the
arrival of P, S,
and surface
waves also
increases with
distance
− Difference in
arrival times of
P and S waves
can be used to
estimate
distance from
earthquake 126
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
• Earthquake size can be determined
by measuring the amplitude (height)
of the seismic waves
− Equations take account of distance and
materials
amplitude
127
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
• Time it takes seismic waves to reach a seismograph
station increases with distance from the focus
Explain what
this figure
shows.
128
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
• Compare these figures.
129
Seismic Waves and Earthquake Detection
The Good Earth/Chapter 5: Earthquakes
• Time it takes seismic waves to reach a
seismograph station increases with distance
from the focus− Time interval
between the arrival
of P, S, and surface
waves also
increases with
distance
− Difference in arrival
times of P and S
waves can be used
to estimate distance
from earthquake
Example: Denver is
closer to epicenter130
Earthquake Conceptest
The Good Earth/Chapter 5: Earthquakes
Suppose you were near an epicenter of an
earthquake and felt the earth move as if you
were in the ocean. What type of seismic
wave would you have experienced?
A. P-wave
B. S-wave
C. Rayleigh wave
D. Love wave
131
Earthquake Conceptest
The Good Earth/Chapter 5: Earthquakes
Suppose you were near an epicenter of an
earthquake and felt the earth move as if you
were in the ocean. What type of seismic
wave would you have experienced?
A. P-wave
B. S-wave
C. Rayleigh wave
D. Love wave
132
Questions to help you review
Chapter 5
133
Earthquake Conceptest
What type of fault generated the
Hebgen Lake earthquake, Montana?
A. Normal fault
B. Reverse fault
C. Strike-slip fault
The Good Earth/Chapter 5: Earthquakes
134
Earthquake Conceptest
The Good Earth/Chapter 5: Earthquakes
Which point on the graph shown below
is most likely a mega-earthquake?
135
Place the phrase in the most
appropriate location on the Venn
diagram.
1. Intermediate and deep focal depths
2. Earthquakes in Gulf of California
3. Frequent earthquake activity
4. Depth increases in direction of plate
motion
5. Earthquakes of magnitude 5 or less are
common
6. More common for US earthquakes
7. Earthquakes off coasts of Alaska,
Washington and Oregon
8. Earthquakes occur along the oceanic
ridge system
9. Shallow focal depths
10. Large magnitude (6+) earthquakes
The Good Earth/Chapter 5: Earthquakes
136
Place the phrase in the most
appropriate location on the Venn
diagram.
1. Most damaging
2. First arrival
3. Last arrival
4. Body wave
5. Raleigh wave
6. 4-6 km/s in crust
7. Second arrival
8. Love wave
9. Particles move in direction of wave
10.Waves generated at time of earthquake
11.On Earth’s surface
12.Determines magnitude
The Good Earth/Chapter 5: Earthquakes
137
Earthquake Conceptest
The Good Earth/Chapter 5: Earthquakes
How much would ground motion
increase between a magnitude 4.5 and
5.5 earthquakes?
A. No increase
B. 5 times as much
C. 10 times as much
D. 30 times as much
138
Earthquake Conceptest
The Good Earth/Chapter 5: Earthquakes
The figures below show the location of a plate
boundary (red line) and the distribution of
earthquake epicenters (filled circles). The size of
the filled circle indicates the earthquake
magnitude.
Which figure
best represents
a convergent
plate boundary
between
oceanic and
continental
plates?139
Earthquake Conceptest
The Good Earth/Chapter 5: Earthquakes
Three sites (L1, L2, L3) record earthquake magnitude
and earthquake intensity for the same earthquake. L1 is
located closest to the focus and L3 is farthest away.
Where is the intensity greatest, and what happens to the
earthquake magnitude calculated at the different sites?
A. Intensity is greatest at L1; calculated magnitude
is the same at each site
B. Intensity is greatest at L3; calculated magnitude
is the same at each site
C. Intensity is greatest at L1; calculated magnitude
decreases with distance from the focus
D. Intensity is greatest at L3; calculated magnitude
decreases with distance from the focus
140