5. A. Stress and Strain…
What are earthquakes?
• natural vibrations of the ground caused by
movement along gigantic fractures in Earth’s crust
6. 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
7. Stress and Strain…
3. What is stress?
… the forces per unit area
acting on a material
… There are three types of
stress.
8. 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
11. Strain!
5. What is strain?
• the deformation
of materials in
response to
stress
• It is represented
by the solid line
on your
diagrams.
12. Elastic Limit
6. A slab of rock’s elastic limit is…
• … the point at which it will
undergo permanent deformation
7. Failure is…
• … when a material breaks!
• We call this failure and
earthquake!
13. 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.
14. 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/anim
ations/faults.htm
http://homepage.ufp.pt/biblioteca/GlossarySaltTectonics/PlatesJPG/Fig.R018-ReverseFault.jpg
15. Reverse Fault – The Himalayas!
http://www.geographicguide.net/earth/pictures/himalayas-asia.jpg
http://img.wylio.com/flickr/500/494666903
16. 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
17. 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
18. 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
23. The Focus of an Earthquake…
1. The focus of an
earthquake is
where the rocks
break at least
several miles
beneath Earth’s
surface.
2. The epicenter is
the location on
Earth’s surface just
above the focus.
http://www.em.gov.bc.ca/Mining/Geoscience/SurficialGeologyandHazards/Earthquakes/PublishingImages/eq-2b.gif
2. Draw the picture.
24. The Focus of an Earthquake…
http://www.em.gov.bc.ca/Mining/Geoscience/SurficialGeologyandHazards/Earthquakes/PublishingImages/eq-2b.gif
25. Earthquake Waves…
1. What are seismic
waves?
• vibrations of the
ground during
an earthquake
Seismic Wave
Rap!
http://www.youtu
be.com/watch?v=
x1tb6HwyaHg
http://gomyclass.com/geology10/files/lecture9/html/web_data/file22.htm
26. Earthquake Waves…
2. How do the following types of seismic waves move
rocks?
a. Primary (P) waves – squeeze
(push) & pull rocks in the same
direction as the wave
http://www.youtube.com/watch?v=2rYjlVPU9U4
http://allshookup.org/quakes/wavetype.htm
27. Earthquake Waves…
2. How do the following types of seismic waves move
rocks?
b. Secondary (S) waves – cause
rocks to move at right angles to
direction of the wave
http://www.youtube.com/watch?v=en4HptC0mQ4
28. Earthquake Waves…
c. Surface waves – move in 2 directions –
up and down and side to side (slowest
and most damaging!)
29. Seismic Waves and a 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.”
30. Seismogram (Add to notes)
http://www.sms-tsunami-
warning.com/pages/seismo
graph#.VFpac3JdVps
31. Travel-Time Graph (not time travel!)
1. A travel-time graph is …
• shows average
travel time of P & S
waves
2. This graph is used to
calculate…
the distance to the
epicenter (using
the difference in
arrival times of the
p and s waves) http://mtweb.mtsu.edu/cribb/100eq.html
32. Travel-Time Curves (p. 501)
Suppose the waves
recorded on a
seismogram at
Station A are farther
apart than they are
at Station B…
The epicenter is farther
from Station A.
Animation for Lab 8 on
next slide
33. Lab Lesson 8 Animation of Waves…
http://aspire.cosmic-
ray.org/Labs/SeismicWaves/
37. Earthquake Magnitude and Intensity
How is the amount of energy released by
an earthquake measured?
• by its magnitude
Haiti, 1/2010 (7)
38. The Richter Scale…
a. The Richter scale is based on…
size of the largest seismic waves
generated by the quake (EQ)
b. Each successive number on this scale
represents…
a 10 times increase in wave size
c. Each increase in magnitude corresponds
to…
A 32-times increase in seismic energy
d. A magnitude 8 EQ releases 32 times
more energy than a magnitude 7 EQ.
40. The Modified Mercalli Scale…
a. The intensity of an earthquake can be
determined by…
amount of damage done to the
structures involved (intensity)
b. The modified Mercalli scale is used to
determine the intensity of an EQ by…
rate damage & other effects as
noted by observers
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
43. Modified Mercalli Scale…
d. A seismic intensity map is made
by…
• … compile the MMsI values
(Modified Mercalli scale intensity
values), plot them on a map, &
join points of similar intensity.
(See map on back.)
• Mercalli values at distances very
far from the epicenter…
Decrease to I
47. Depth of Focus…
e. Another factor that
determines the
intensity of an
earthquake is…
• The depth of an
EQ’s focus
Shallow-focus
events will produce
catastrophic quakes
with high intensity
values.
48. Locating an Earthquake…
1. The distance to an
earthquake’s epicenter is
determined by…
the time difference b/tw
the arrival of the P-wave
& the S-wave
2. This distance is called…
Epicentral distance
3. Three seismograph
stations are needed to
determine an EQ’s
epicenter.
50. Seismic Belts… p. 510
1. Most earthquakes are associated with…
Tectonic plate boundaries
2. 80% of earthquakes occur in…
The Circum-Pacific Belt
3. Another 15% of earthquakes occur at the
Mediterranean-Asian Belt
4. Most of the remaining earthquakes occur at
mid-ocean ridges
http://earthquake.usgs.gov/
58. 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
61. 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
62. Structural Failure…
3. Pancaking is…
• supporting walls
of ground floor
collapse causing
upper floors to
collapse
Pancaked Building in Turkey
63. Structural Failure…
4. Building with 5-
15 stories may
collapse because…
• their natural
sway has the
same vibration
period of an EQ
http://www.wbdg.org/resources/seismic_design.php
66. Land and Soil
Failure…
5. Earthquakes in
sloping areas
can trigger…
• landslides!
El Salvador, 2001, mag 7.6
67. Land and Soil Failure
6. Soil liquefaction
• subsurface
materials liquefy
& behave like
quicksand due to
EQ vibrations
http://earthquake.usgs.gov/learn/animation
s/animation.php?flash_title=Liquefacti
on&flash_file=liquefaction&flash_width
=450&flash_height=200
http://en.wikipedia.org/wiki/Soil_liquefaction
70. Land and Soil Failure…
7. There was much
damage to
structures in the
Mexico City EQ
of 1985 b/c...
It is built on
soft
sediments.
http://seismo.berkeley.edu/blogs/seismoblog.php/2008/09/19/title
71.
72. Fault Scarps…
8. A fault scarp is…
• area of great vertical offset where the
fault intersects Earth’s surface.
9. The fault scarp shown created a…
• waterfall
73. Tsunamis…
10. A tsunami is caused by…
• vertical motion of seafloor (during the EQ)
bumps the water over the fault
11. A tsunami in the open ocean is usually…
• 1 meter high (3 ft)
• You wouldn’t notice it if you were there!
Tsunami strikes Ao Nang, Thailand
http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami
74. Tsunamis…
12. A tsunami is dangerous when it enters
shallow water because…
• it moves very fast
• it can be very high – up to 30m (90 ft)!
Sri Lanka, 2004
75.
76. Tsunamis…
13. The most recent devastating tsunami
was in…
• Japan, March 2011
Youtube Clip:
https://www.youtub
e.com/watch?v=V2t
aJExhV6g
82. Seismic Risk…
14a. Five states with
the greatest seismic
risk…
• Alaska
• California
• Hawaii
• Utah
• Nevada
b. The San Andreas
Fault is a
transform boundary. http://pubs.usgs.gov/fs/2005/3052/images/map.jpg
83. Seismic Risk…
14c. The seismic risk
of the NC
Piedmont and
mountains…
• moderate
14d. The seismic
risk of the coastal
plains of NC…
• low
86. Earthquake Prediction…
16. Seismic gaps are
• sections of
active faults that
haven’t had big
EQs for a while
• An earthquake
is likely to
happen here!
The San Andreas Fault
http://upload.wikimedia.org/wikipedia/commons/8/8d/San_Andreas.jpg
87. Earthquake Prediction…
17. Why is earthquake prediction important?
… to save lives and
prevent property
damage!!
http://www.youtube.com/watch?v=_YLjIvJXhpg
San Andreas Fault
89. 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
90. 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
91. 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!
92. G. Earth’s Internal Structure …
http://astronomy.nju.edu.cn/~lixd/GA/AT4/AT407/HTML/AT40703.htm
