ESC1000 • Earth Science • Summer 2016esc1000summer.weebly.com/.../5/...and_earthquakes.pdf · Plate Tectonics Conceptest The Good Earth/Chapter 4: Plate Tectonics Which of the

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




• 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




• 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


• 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


Which is the actual map of Earth’s features?

10

Continental Drift


• 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


12

Matching features

• A continuous

mountain belt can

be formed when

Pangaea is

reassembled


Continental Drift


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



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



15

Continental Drift


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


How is fixing this plate analogous to

Wegener’s methods of assembling the

continents into Pangaea?

17



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



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


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


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:

http://highered.mheducation.com/sites/0073524107/student_view0/chapter4/how_seafloor_spreading_creates_magnetic_polarity_stripes.html

http://highered.mheducation.com/sites/0073524107/student_view0/chapter4/magnetic_reversals_at_mo_ridge.html

https://www.youtube.com/watch?v=D69hGvCsWgA

1. Seafloor Topography


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



• Continental shelf

− Narrow, shallow

ocean surrounding

continents

• Abyssal plain

− Relatively level

seafloor, often with

volcanoes (Bermuda)

24



• 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



• 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


• 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


28

3. Heat Flow


hottercooler

• Heat flow varies

systematically

around the

world

− Highest along

oceanic ridges

− Lowest on

continents and

in ocean far

from ridges

29

4. Volcanoes


• 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)


• Most active

volcanoes

are found

near oceanic

trenches

31

5. Earthquakes


• 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)


• 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


• 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


• 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


− 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


• 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


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



39

Plate Boundaries

Divergent

Transform

Convergent



40

Plate Boundaries


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


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


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


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


Transform Boundaries

• Link sections of ridge or trench systems

• Plates move in opposite directions

• No lithosphere created, no lithosphere destroyed

45

Plate Boundaries


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


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

http://highered.mheducation.com/sites/0073524107/student_view0/chapter4/seafloor_spreading.html


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


Interpretations

49


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


Interpretations

50

Evidence from the Seafloor


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



Polarity of seafloor alternates

between normal and reverse

on either side of oceanic ridge

Observations &

Interpretations

52

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


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


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


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


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


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


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


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


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


How many plates are in this image?

A. 1

B. 2

C. 3

D. 4

E. 5

62

In-Class Activity 2: Part C


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



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



Which image best approximates the shape

of the ocean floor in the Atlantic Ocean?

66



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



How many plates are in this image?

A. 3

B. 4

C. 5

D. 6

68



The continental crust at Y is moving toward the …

A. Southeast

B. Southwest

C. Northeast

D. Northwest

69



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).


71



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



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



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

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


• 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


• 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



• 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



• 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



• 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


What do you observe in these images?

85



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



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:

http://highered.mheducation.com/sites/0073524107/student_view0/chapter5/earthquakes.html

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


88


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


89

Types of Faults


− 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



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


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


3524107/student_view0/chapter5/earthqua

kes.html

Earthquake Measurement: Magnitude


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


• 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


• 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



using the Modified

Mercalli Scale

− Difficulties in

comparing earthquakes

from different regions

due to contrasts in

Population density

Building codes

Ground materials

Distance


96



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


97

Extra slides you may wish to

use for reference in completing

Part D of In-Class Activity 2:

98



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



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



• 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



• 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




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




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



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



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


• 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


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


• 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


• 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


− 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


• 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


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


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


• Tsunami damage, northwestern Sumatra

Waves reached 31 m elevation

115

Earthquake Hazards


• 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


• 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


• 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


• 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



− 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:


73524107/student_view0/chapter5/seismo

meter_2.html

http://highered.mheducation.com/sites/0073524107/student_view0/chapter5/seismometer_2.html

Types of Seismic Waves


− 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:

http://highered.mheducation.com/sites/0073524107/student_view0/chapter5/earthquake_waves.html



• 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



• 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



• 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



• 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



• Earthquake size can be determined

by measuring the amplitude (height)

of the seismic waves

− Equations take account of distance and

materials

amplitude

127



• Time it takes seismic waves to reach a seismograph

station increases with distance from the focus

Explain what

this figure

shows.

128



• Compare these figures.

129



• 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



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



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


What type of fault generated the

Hebgen Lake earthquake, Montana?

A. Normal fault

B. Reverse fault

C. Strike-slip fault


134



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


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


137



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



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



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

Documents

ESC1000 • Earth Science • Summer 2016esc1000summer.weebly.com/.../5/...and_earthquakes.pdf · Plate Tectonics Conceptest The Good Earth/Chapter 4: Plate Tectonics Which of the