Goal 2.1 Earthquakes

Shake, Rattle, and Roll!

Lesson 7

Forces and Faults

Think About It…

What happens to a rubber band that is stretched past

its elastic limit?

Focus Question…

What causes earthquakes?

A. Stress and Strain…

What are earthquakes?

• natural vibrations of the ground caused by movement along gigantic fractures in Earth’s crust

Stress and Strain…

1. When do most earthquakes occur?

• when rocks fracture (break) deep within Earth

2. When do fractures form?

• when stress exceeds the strength of the rocks involved

Stress and Strain…

3. What is stress?

… the forces per unit area acting on a material

… There are three types of stress.

Stress Compression decreases the volume of a

material – occurs at convergent boundaries

http://rst.gsfc.nasa.gov/Sect2/05-01_reverse_fault-jyougashima_DSC8766.jpg

Stress! Tension pulls a material apart –

at divergent boundaries

Stress!

Shear (horizontal)

causes a material to twist – at transform

boundaries.

http://rpmedia.ask.com/ts?u=/wikipedia/commons/thumb/b/b1/Boudin_vein.jpg/180px-Boudin_vein.jpg

Strain!

5. What is strain?

• the deformation of materials in response to stress

• It is represented by the solid line on your diagrams.

Elastic Limit

a. A slab of rock’s elastic limit…

• … is the point at which it will undergo permanent deformation

b. At failure…

• … a material breaks!

• We call this failure and earthquake!

Faults… 1. Rocks will fail and form a fault…when stress is

applied too quickly or when stress is great

2. A fault is the resulting fracture or system of fractures along which movement occurs.

Reverse Fault…

Is caused by…

compression (at a convergent boundary)

Movement of crust…

block above fault moves up and over

http://www.iris.edu/gifs/animations/faults.htm

http://homepage.ufp.pt/biblioteca/GlossarySaltTectonics/PlatesJPG/Fig.R018-ReverseFault.jpg

Reverse Fault – The Himalayas!

http://www.geographicguide.net/earth/pictures/himalayas-asia.jpg

http://img.wylio.com/flickr/500/494666903

Normal Fault…

Is caused by…

tension (at a divergent boundary)

Movement of crust…

block above fault moves down http://www.iris.edu/gifs/animations/faults.htm

http://geology1a-1.wikispaces.com/file/view/NormalFault.gif/90969209/NormalFault.gif

Normal Fault – The Sierra Nevadas

http://fela2fela.files.wordpress.com/2012/02/sierra-nevadas.jpg

http://www.pbs.org/weta/thewest/places/states/california/ca_sierra.jpg

Strike-slip Fault…

Is caused by…

horizontal shear (at a transform boundary)

Movement of crust…

blocks slide past each other

horizontal (no vertical movement) http://www.iris.edu/gifs/animations/faults.htm

http://7bcore3.wikispaces.com/file/view/StrikeSlipLLFault%5B1%5D.gif/193098468/StrikeSlipLLFault%5B1%5D.gif

The San Andreas Fault…

http://www.sanandreasfault.org/

Lesson 8

Seismic Waves and Earth’s Interior

Think About It…

Is it possible to go to Earth’s core?

Focus Question…

What do seismic waves tell us about Earth’s interior?

The Focus of an Earthquake… 1. The focus of an earthquake is where the rocks break and it

is located at least several miles beneath Earth’s surface. 2. The epicenter is on Earth’s surface just above it.

http://www.em.gov.bc.ca/Mining/Geoscience/SurficialGeologyandHazards/Earthquakes/PublishingImages/eq-2b.gif

2. Draw the picture

C. Earthquake Waves…

1. What are seismic waves?

• vibrations of the ground during an earthquake

2. How do the following types of seismic waves move rocks?

a. Primary (P) waves – squeeze and pull rocks in the same direction along which the waves are traveling

b. Secondary (S) waves – cause rocks to move at right angles in relation to direction of waves

c. Surface waves – move in 2 directions – up and down and side to side (slowest and most damaging!)

d. See next slide…

Earthquake Waves…

3. P-waves and S-waves pass through Earth’s interior.

http://gomyclass.com/geology10/files/lecture9/html/web_data/file22.htm

D. Seismic Waves and Earth’s Interior…

a. Seismology – the study of earthquakes

b. Seismologist – studies earthquakes

c. Seismometer – detects/records earthquakes

d. Seismogram – record of an earthquake

“Seismo-” is Latin for “shaking.”

Seismogram… http://www.geo.mtu.edu/UPSeis/reading.html

“So which wiggles are the earthquake? The P wave will be the first wiggle that is bigger than the rest of the little ones (the microseisms). Because P waves are the fastest seismic waves, they will usually be the first ones that your seismograph records. The next set of seismic waves on your seismogram will be the S waves. These are usually bigger than the P waves.

The surface waves are the other, often larger, waves marked on the seismogram. Surface waves travel a little slower than S waves (which, in turn, are slower than P waves) so they tend to arrive at the seismograph just after the S waves.”

E. Travel-Time Curves (not time travel!)

1. Which waves always arrive first at a seismic facility?

• P-waves (Primary means “first.”)

2. Travel-time curves show…

• The average travel time of P and S waves for different distances

http://mtweb.mtsu.edu/cribb/100eq.html

Travel-Time Curves (p. 501)

3. Waves recorded on seismograms

from more distant facilities are farther apart

than waves recorded on

those closer to the epicenter.

Lesson 9

Measuring and Locating Earthquakes

Think About It…

What is the strongest earthquake that has

happened in your lifetime?

Focus Question…

How are earthquakes measured and located?

Earthquake Magnitude and Intensity

How is the amount of energy released by an earthquake measured?

• by its magnitude Haiti, 1/2010 (7)

The Richter Scale…

a. The Richter scale is based on… a. The size of the largest seismic waves

generated by the quake

b. Each successive number in the represents… a. An increase in seismic-wave size of a factor of

10

c. Each increase in magnitude corresponds to… a. A 32-fold increase in seismic energy

d. A magnitude 8 EQ releases 32 times more energy than a magnitude 7 EQ.

The Richter Scale

http://sahanasingh.wordpress.com/2011/05/17/failing-to-prepare/

Haiti, 1/2010 (7)

Japan, 3/2011 (9)

The Modified Mercalli Scale…

a. The intensity of an earthquake can be determined by… a. The amount of damage done to the structures

involved

b. The modified Mercalli scale is used to determine the intensity of an EQ by… a. Rating the types of damage and other effects

of an earthquake as noted by observers

c. This scale uses Roman numerals from I to XII. It was developed by Giuseppe Mercalli in 1902.

http://www.geo.mtu.edu/UPSeis/intensity.html

Modified

Mercalli

Scale…

http://scearthquakes.cofc.edu/images/MercalRichtscale.gif

Modified Mercalli Scale…

e. Earthquake intensity depends on…

• the amplitude of the surface waves generated

f. Mercalli values at distances very far from the epicenter…

• Decrease to I

g. A seismic intensity map is made by…

• Compiling the Modified Mercalli scale intensity values, plotting them on a map, and joining points of similar intensity with contour lines.

Seismic

Intensity

Map…

Northridge,

California

Earthquake

http://seismo.berkeley.edu/blogs/seismoblog.php/2009/01/17/today-in-earthquake-history-northridge-1994

http://www.weldreality.com/northridge-earthquake-4.jpg

Damage in Northridge, Ca…

More Damage in Northridge, Ca…

Depth of Focus…

h. Another factor that determines the intensity of an earthquake is…

• The depth of an EQ’s focus

i. Shallow-focus events will produce catastrophic quakes with high intensity values.

Locating an Earthquake…

1. The distance to an earthquake’s epicenter is determined by…

1. the P-S wave separation (the time difference b/tw the arrival of the P-wave and the S-wave)

2. This distance is called…

1. Epicentral distance

3. Three seismograph stations are needed to determine an EQ’s epicenter. See next slide…

Locating an Earthquake…

http://www.geo.mtu.edu/UPSeis/images/triangle.gif

5. A travel-time graph determines the exact time of an EQ.

Seismic Belts…

1. Most earthquakes are associated with… 1. Tectonic plate boundaries

2. 80% of earthquakes occur in…

1. The Circum-Pacific Belt

3. Another 15% of earthquakes occur at the 1. Mediterranean-Asian Belt

4. Most of the remaining earthquakes occur in narrow bands that run along the crests of ocean ridges.

http://earthquake.usgs.gov/

http://oceanworld.tamu.edu/resources/oceanography-book/earthquakes.htm

Lab 9 USA

Map…

http://www.worldatlas.com/geoquiz/mississi.gif

Northridge,

California

Earthquake

Color Sheet

Lesson 10

Earthquake Hazards

Think About It…

Why do developing countries such as Haiti suffer such devastation

from earthquakes?

Focus Question…

How do earthquakes affect the four spheres of Earth?

Structural Failure…

1. The types of buildings that sustain the most severe damage from earthquakes are…

• unreinforced made of stone, concrete, or other brittle materials

Typical building in Iraq

http://www.siampinoy.net/forum/55-ano-ba-ang-latest-post-it-here/88292-chile-earthquake-may-have-shortened-days-on-earth.html

Church, Armenia, 1988

Structural Failure…

2. The types of buildings that sustain the least amount of damage from earthquakes are…

• wooden

• high-rise, steel-framed

Kobe, Japan 1995

Structural Failure…

3. Pancaking is…

• when supporting walls of the ground floor collapse and cause the upper floors to fall and collapse

Pancaked Building in Turkey

Structural Failure…

4. Building with 5-15 stories may collapse because…

• their natural sway has the same period of vibration as the EQ

http://www.wbdg.org/resources/seismic_design.php

Land and Soil

Failure…

5. Earthquakes in sloping areas can trigger…

• landslides!

El Salvador, 2001, mag 7.6

Land and Soil Failure…

6. Soil liquefaction is… • when subsurface

materials liquefy and behave like quicksand due to the seismic vibrations of an EQ

7. Seismic waves are amplified in soft materials because… • they have little

resistance to deformation

http://en.wikipedia.org/wiki/Soil_liquefaction

http://en.wikipedia.org/wiki/File:Liquefaction_at_Niigata.JPG

Land and Soil Failure…

8. Because Mexico City is built on soft sediments, there was much damage to structures there during the 1985 EQ.

http://seismo.berkeley.edu/blogs/seismoblog.php/2008/09/19/title

Fault Scarps…

9. A fault scarp is…

• an area of great vertical offset where the fault intersects the ground surface.

11. The fault scarp shown created a…

• waterfall

Tsunamis…

12. A tsunami is caused by…

• the vertical motions of the seafloor displacing the entire column of water over the fault

13. A tsunami in the open ocean is usually…

• 1 meter high

14. You probably wouldn’t notice it if you were there!

Tsunami strikes Ao Nang, Thailand

http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami

Tsunamis…

15. A tsunami is dangerous when it enters shallow water because…

• it moves very quickly

• it can be very high – up to 30m!

Sri Lanka, 2004

http://i424.photobucket.com/albums/pp322/estoy26/ig14_earthquake_15_02.jpg

Tsunamis…

16. The most recent devastating tsunami was in…

• Japan, March 2011

Seismic Risk…

17. Most earthquakes occur at…

• tectonic plate boundaries

Seismic Risk…

18a. Five states with the greatest seismic risk…

• Alaska

• California

• Hawaii

• Utah

• Nevada

http://pubs.usgs.gov/fs/2005/3052/images/map.jpg

Seismic Risk…

18b. The seismic risk of the NC Piedmont…

• moderate

18c. The seismic risk of the coastal plains of NC…

• minor

Earthquake Prediction…

19. Earthquake prediction is based on studies of… • probability • that is, where are EQs most likely to

occur based on where they have occurred in the past

20. Earthquake recurrence rates indicate …

• that the fault involved ruptures repeatedly at regular intervals to generate similar quakes

Earthquake Prediction…

21. Seismic gaps are …

• sections of active faults that haven’t experienced significant EQs for a while

22. An earthquake is likely to happen here!

The San Andreas Fault

http://upload.wikimedia.org/wikipedia/commons/8/8d/San_Andreas.jpg

Earthquake Prediction…

23. Another factor used to determine EQ probability is…

• the rate at which strain build up in rocks

http://www.nature.com/nature/journal/v473/n7346/images/473146a-i2.0.jpg

Earthquake Prediction…

24. Why is earthquake prediction important?

… to save lives and prevent property

damage!!

F. Clues to Earth’s Interior (p. 503)

1. Where does the knowledge of Earth’s interior come from?

• The study of seismic waves

2. How do P-waves and S-waves move through the mantle?

• They follow fairly direct paths

3. What do P-waves do when they strike the core?

• They bend

4. Why don’t S-waves enter Earth’s core?

• They cannot travel through liquids

Clues to Earth’s Interior

5. What does the disappearance of S-waves tell us about Earth’s outer core?

• That it must be liquid

6. What shows us that Earth’s inner core is solid?

• Studies of how P waves are deflected deep within Earth

http://www.columbia.edu/~vjd1/ray_paths.gif

G. Earth’s Internal Structure…

Crust of lithosphere – granite (continental crust), basalt (oceanic crust)

Upper mantle – peridotite (intrusive, bumpy, igneous)

Asthenosphere – peridotite

Lower mantle – oxides of iron, silicon, and magnesium

Core – iron and nickel (magnetic field is generated here!

G. Earth’s Internal Structure …

http://astronomy.nju.edu.cn/~lixd/GA/AT4/AT407/HTML/AT40703.htm