Earth’s Dynamic Crust 3-21-14
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Aim: What is meant by “Dynamic Crust” and
what evidence can we observe to support it?
Do Now
1. Open your review books to p. 245
2. In Figure 12-1 Diagram D label layers 2,3,4, and
5 using your scheme for sedimentary rock
identification (ESRT)
3. Which of these numbered layers do you think
is the oldest, why?
HW: R+H 244-245, A+E 1-8
Assumptions:
 Uniformitarianism – The same processes that
shaped the earth in the past are the same
processes shaping the earth today.
 Original Horizontality - sedimentary rocks and
extrusive igneous rocks form in flat, horizontal
layers called normal strata.
 Superposition – the oldest rock layers will be the
deepest in the Earth (upset only by overturning and
thrust faults)
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Normal Strata
Convection
currents in the
mantle put stress
on the crust
causing it to
move and crack.
Cracks join up to
create crustal
plates.
Earth’s outer shell is layers of solid
rock called the crust.
Because of the constant stress put on the
crust it becomes cracked (creating fault
lines and crustal plates).
 When there is movement along a fault an
earthquake is produced which can cause
volcanic activity or mountain building.
 These fault lines on the earth are known
as “zones of crustal activity, earthquake
belts or earthquake zones”
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Crustal Disturbances- are the result
of convection currents in the mantle
constantly putting stress on the
crust (pushing and pulling).
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Types of Stress:
1. Compression – two strata moving
towards one another, causes reverse faults
2. Tension – two strata moving away from
one another, causes normal faults
3. Shearing- two strata moving laterally with
respect to one another, causes lateral faults
Rock Layers which no longer show
original horizontalitiy are referred to as
disturbed
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There are three kinds of disturbed strata
1. Folded – bent or curved layers
Anticline
Occurs Because Rock Types Are Ductile – Bend
Easily and are being compressed.
Syncline
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2. Faulted Strata – a break has occurred in the
horizontal layer
Foot wall is
underneath
the fault.
This occurs because the rocks are brittle or
easily broken. This is tension (although
could also compress reversing the fault.
Hanging
wall rests
on the fault.
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3. Tilted Strata – rocks appear diagonal or
slanted
Caused by compression.
All three of these types of disturbed strata
are evidence for crustal movement
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There is one more piece of evidence…
Eurypterus Remipes (and other fossils)
◦ Marine fossil found on top of mountains in NYS
◦ Shows evidence of crustal uplift.
◦ Shallow water fossils at deep ocean depths.
So…
What do you think we mean when we say
“Dynamic Crust”
 What have we learned about today that
can support this?
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Aim: What is an Earthquake?
3-25-14
Do Now:
R&H pp.246-249.
 1 What is an earthquake?
 2. . What is the difference between P,S and
L waves?
HW: Finish Lab.
Parts of an Earthquake
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Fault – crack along which movement occurs.
Focus- point of origin where initial motion takes
place.
Epicenter- point on surface directly above focus.
Seismic waves- shock or vibrational waves coming out
of the focus or epicenter.
Seismic Waves- produced by an earthquake.
S-Waves
P-Waves
 Also called secondary
 Also called primary
waves or shear waves
waves or compressional
because they cause
waves
most of the shaking
 Faster so first to arrive
 Slower so always arrive
 Travel through all
after P-Waves
materials
 Travel through SOLIDS
 Comes from the focus
ONLY
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Comes from the focus
Surface Waves or L-waves
• Slowest kind of wave which travels along the
surface of the earth starting at the epicenter
• Travels like ripples in a pond and can cause
significant damage
How are earthquakes classified?
Richter Scale
 Rated 1 to 10
 Measures EQ magnitude or
power so each EQ has
only one value.
 Largest EQ ever recorded
was an 9.5 on the Richter
Scale (Chile 1960)
Mercalli Scale
 Rated by intensity or
damage 1 to 12
 Based on what you would
feel in one area so one EQ
can have many intensities
 1 detected only by
seismographs and 12 is
total destruction
Aim: How do we measure an 3-26-13
earthquake?
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1.
2.
3.
Do Now:
Which scale measures earthquake power?
Where do P, S, and L waves originate?
Where on the surface will the most shaking be
experienced during an earthquake and why?
HWFinish Lab
Seismograph
Machine used to measure seismic
waves
Seismogram
Reading from seismograph
Practice
Figure out the difference between the P
and S wave arrival times on the board for
each seismogram.
 If the difference in P and S wave arrival
times increases with distance from the
epicenter, then which seismogram came
from the seismograph station closest to
the earthquake?
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animation - epicenter - #E03C33
How to use the seismogram to
find an earthquake epicenter
1. Determine the difference in arrival time
from the P wave and the S wave.
 2. Use the ESRT p.11to determine the
epicenter distance and the P wave travel
time.
 3. Subtract the P wave travel time from the
P wave arrival time to determine the
earthquake origin time.
 4. Draw a circle around the city with your
epicenter distance as the radius.
 5. Do this for 3 seismic stations to pin point
the location of the epicenter.
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Locating Epicenters-Triangulation
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One seismic
station can give us
the distance only.
Two seismic
stations can give
us distance and 2
possible locations.
Three seismic
stations can
pinpoint an exact
location for an
epicenter.
What do we know?
1.
2.
3.
How long does it take for:
a. an S wave to travel 7,000 kilometers (km)
b. a P wave to travel 2,600 km
If the P wave arrives 5 minutes and 20 seconds after
the earthquake actually occurs, how far away from the
epicenter are you?
How many seismic station readings do you need to
confirm the location of an earthquake epicenter?
3-28-14
Aim: How can we use the Mercalli Scale to find an
earthquake epicenter?
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Do Now
1. What information can be determined about an
earthquake from a single seismic station?
2. As distance from the epicenter increases what
happens to difference in arrival times of P & S
waves?
3. How many seismic stations are needed to
confirm an epicenter location?
4. What is the Mercalli scale?
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HW: R&H pp.246-252, A&E #9 – 28.
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3-31-14
Aim: What does a model of the earth’s interior
look like?
Do Now
1. How can earthquake magnitude be
measured?
2. March 21st was a special earth science
day. Tell me all you know about it.
3. If we cannot physically drill to the center
of the earth, how can we know what it
looks like?
HW: R&H pp.246-252, A&E #9 – 28.
R&H 255-258 A&E 29-41
Volcanoes
Cinder Cone
Composite
Emergency Planning
Earthquakes cannot be
predicted
 If you ever find yourself in
an earthquake “drop, cover,
and hold” under a strong
object or in a doorway.
 Proper building codes are
required in areas prone to
EQ’s such as type of rock
underneath the building
and materials used to
construct the building
 Always have a disaster plan
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Volcanoes can be predicted
by measuring the small
earthquakes leading up to
an eruption and the
swelling of the ground.
 Always have a disaster plan
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Tsunami warnings may
offer a few hours notice.
 Get to higher ground and
find a secure structure.
 The water recedes
significantly before the
waves start approaching.
 Always have a disaster plan
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A Model of the Earth’s Interior
Properties of the earth’s
interior were inferred by
studying seismic waves
A wave’s speed will
increase if the pressure or
the density of the material
it travels through are
increasing
As the density of a
material changes in each
layer the wave is bent or
refracted.
S- waves cannot travel
through the liquid outer
core and shadow zones
where no waves are
receceived are created.
We know the inner core is
made of iron and nickel
from studying meteorites
that have hit the earth.
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The Moho is a
boundry between the
crust and the mantle at
which waves refract.
The asthenosphere or
the plastic mantle is
the solid part of the
mantle with the ability
to flow (has plasticity),
this is where
convection causes the
plates to move.
As depth increases in
the earth, so does
pressure, density, and
temperature.
Plate Tectonics
4-4-14
Aim: What are the three types of plate boundaries and how
have they formed the world we see today?
 Do Now:
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1. Using the diagram below please label the following; disturbed or
undisturbed, oldest rock layer, foot wall, hanging wall, the stress
(tension, compression, or shearing), type of fault, property of the rocks
(brittle or ductile)
2.
3.
Explain how you could find a marine fossil on a mountain top or a
shallow water fossil at great ocean depths.
How do we know the inner core is made of iron and nickel?
Continental Drift
http://www.youtube.com/watch?v=hSdlQ
8x7cuk
 Continental Drift – the theory that the
continents were all once together and are
slowly drifting apart.
 Plate Tectonics – Earth’s lithosphere is
broken up into plates which are
constantly moving. (driven by convection
cells in the mantle)
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Diverging Boundaries-plates are
pulling apart.
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Seafloor spreading creates new ocean crust
at mid ocean ridges. Crust is youngest here.
Converging Boundaries-plates are
pushing together.
Island Arcs, mountain ranges and ocean trenches
can be formed.
Continental crust which is always thicker and less
dense will uplift and thinner, denser oceanic crust
will always subside (go down) or subduct (slide
beneath another plate)
Transform Boundaries-plates are sliding
horizontally past one another like the San
Andreas Fault in CA.
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Shearing tension builds up in the crust and is released
periodically causing transform fault earthquakes
Aim: What evidence do we have for
continental drift?
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1.
4-7-14
Do Now:
Name each of the three plate boundaries, the kind of
stress which forms them, and the geological features seen
at each one
HW: R&H pp.259-267, A&E #42-68. Topic 12 Exam Wed.
Island Arcs vs. Island Chains
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Island Arcs
Occur along Convergent
plate boundaries
Formed by rising magma
from melted subducting
plate.
Ex. The Aleutian Islands
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Island Chains
Occur over Hot Spots
in the Earth’s mantle.
Formation of the
Hawaiian Islands
Four Pieces of Evidence That Support
Continental Drift and Plate Tectonics
1. Puzzle Like Fit of the Continents
3. Matching Rock Formations
2. Matching Fossils on Different Continents
4. Glacial Deposits
Magnetic Reversal
In a diverging oceanic plate boundary cooling
rocks orient themselves to magnetic north.
 Over time, about every100,000 years,
magnetic north has switched from the
geographic north pole to the geographic
south pole and back again.
 Geologists can match these orientations on
either side of the plate boundary to show
evidence of Seafloor Spreading.
 Youngest rocks are found at the ridge and as
distance from the ridge increases, age of the
rock increases. www.youtube.com/watch?v=#1F061D
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Date: 3/30/11
Aim: What causes a tsunami?
Do Now:
1. What is a tsunami?
2. Take out your laptops
3. Go to the class website
4. Look for the new page titled “Tsunami
Detectives”
HW: Fill in your “Tsunami Detective”
Worksheet for the recent tsunami in
Japan
Study for Friday’s Test:Topic 12
Learning Objectives
1.
2.
What causes a
tsunami?
How are tsunamis
related to the
earthquakes we
studied yesterday
and how are they
related to the
concept of a
dynamic crust?
Lab Practical
Consists of 3 stations.
 You will have 9 minutes at each station to
complete the activities.
 You may not go back to a station after
time is up.
 You will be scored on accuracy and
completeness.
 There will be a station on Earthquake
Epicenters, Ellipses and Rocks & Minerals.
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