Download a. Transverse or Shear wave

I.
Earth Structure
A.
Inner Core
Solid;
1480 km diameter
Mostly Ni and Fe
Why is it solid even though it’s hot enough to melt
any rock?
B.
Outer Core
Plastic/ Liquid;
Mostly Ni and Fe
C.
D.
1990 km thick
Mantle
2865 km thick;
Made of three distinct layers:
1.
Mesosphere
Most of Mantle
Non-Newtonian substance
2.
Asthenosphere
Liquid/ slippery
Mohorovicic Discontinuity
(Moho)- where seismic waves slow down
3.
Lower Lithosphere
Broken Solid/ brittle
Crust
Solid;
broken into pieces called plates
Mostly silica (quartz)
rigid, with some flexibility
1.
Two types:
a.
Oceanic Crust
More dense of the two; about 5 km thick
Basaltic composition (mafic chemistry)
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b.
II.
Continental Crust
Less dense with more silica; about 35 km
thick
Granitic composition (felsic chemistry)
Do Plates really move?
Past/ Indirect Evidence of Plate Tectonics
A.
Distorted Rock Layers
1.
B.
Folding & Tilting
a.
Principle of Original Horizontality
c
b.
Syncline
c.
Anticline
d.
Geosyncline
b
Fossil Evidence
1.
Marine reptile found on the East Coast
of South America and West Coast of Africa;
unable to swim across the open ocean
2.
Corals
What do corals need to survive?
Why are they found in Wisconsin?
3.
Ammonites & Belemnites in Montana?
4.
Marine shells on top of the Himalayas?
III. Present/ Direct Evidence of Plate Tectonics
2
A.
Earthquakes
B.
Displaced structures
like fences, buildings, rivers
C.
Volcanoes
IV. So the Plates move, How do they do it?
A.
V.
Convection Currents in the Mantle
The Physics of Plate Tectonics
A.
Forces acting on the crust
1.
2.
Tension Forces
a.
Push or pull away from each other along a
single line of motion
b.
Divergent Boundary/ Rift
Compression Forces
a.
A push towards one another in a single line
of motion
b.
Convergent Boundary
Orogeny (mountain building)
1.
Subduction Zone
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3.
Shear Forces
a.
Forces that act in opposite directions along
different lines of motion. Like a scissors
b.
Plates sliding past one another
VI. So the Plates move, WHAT Happens now?
Joints VS. Faults; Landforms; Earthquakes
A.
Diastrophism the process by which the earth’s
surface is reshaped by movement of the crust
B.
Jointsare breaks or fractures in bedrock along
which NO movement has taken place
C.
Faults- are breaks or fractures in bedrock along
which movement HAS taken place
1.
Parts of a Fault
a.
Footwall- the underlying surface of
an inclined fault plane. Can act like a wedge
b.
Hanging Wall- the overlying surface
of an inclined fault plane
b
a
D.
Types of Faults
1.
Dip-Slip- a fault in which movement is
parallel to the dip of the fault surface
FYI: Dip is the angle and direction at which a
plane is inclined from horizontal
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a.
b.
2.
Normal Dip-Slip The hanging wall block
has moved DOWN relative to the footwall
1.
Caused mostly by TENSION forces
2.
Divergent boundary
Reverse Dip-Slip The hanging wall block
has moved UP relative to the footwall
1.
Caused mostly by COMPRESSION
2.
Convergent boundary
Lateral or Strike-Slip
A fault in which the fault
block movement is parallel to the strike of the
fault surfaces.
FYI: Strike is the compass direction of a line by the
intersection of an inclined plane with the
horizontal plane
3.
a.
Mostly horizontal displacement, there is little
or no vertical movement
b.
Caused by SHEAR forces
Oblique-Slip a fault having both strike-slip and
dip-slip components, where plates move away
from each other
a.
Rifting and Sea Floor spreading result from
this kind of fault.
b.
Caused by TENSION forces
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c.
E.
Divergent boundary
Landforms from Crustal Movement
1.
Mountains
defined as a mass of rock rising
more than 600 meters above the surrounding land
a.
Fold Mountains
usually made mostly of
sedimentary rock folded by compression.
World’s tallest and most common mountains
1.
Examples: Appalachians, Rockies,
Alps, Himalayas
b.
F.
Fault-Block Mountains formed by a series
of Normal Dip-Slip faults.
Some of the greatest mountain Ranges
1.
Examples: Sierra Nevada (California),
Grand Teton (Wyoming),
Wasatch (Utah)
When the Earth Shakes- Earthquakes
1.
Can be caused by volcanic eruptions, but more
often, faulting...
a.
Faulting the movement of rock along a fault
b.
Elastic Rebound
occurs when tremendous
pressure causes plates to move and the rock
layers shake back and forth
1.
Seismic Waves are waves of
vibrations sent out in all directions from
the focus
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2.
3.
Where do Earthquakes start?
a.
Focus
the point below the surface where
the rocks break and move
b.
Epicenter the point on the surface, directly
above the focus
How are Earthquakes measured?
a.
Seismograph is an instrument that detects,
measures, and records the seismic waves
produced by earthquakes
1.
Operates on Newton’s First Law of
Motion
2.
Seismogram is the recorded
information and looks like a zig zag line
a
4.
Anatomy of a Wave
a.
Crest
the highest point on a wave
b.
Trough
the lowest point on a wave
c.
Amplitude
refers to the distance from the
midpoint to the crest (or trough)
d.
Wavelength is the distance from the top of
one crest to the top of the next
or the distance between any successive
identical part of the wave
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b
e.
5.
Frequency
often called Hertz, is the
number of vibrations (cycles) per second
Types of Seismic Waves
a.
BODY WAVES:
are waves which can
travel through the body of the earth
1.
Primary Waves
AKA P-Wave; are a
type of Longitudinal wave. It causes back
and forth particle motion; it follows the same
direction as the energy transfer
2.
a.
They are a type of Compressional
Wave (sound is this type)
b.
Will travel through solid, liquid,
and gas; must have a medium
c.
Travels 7.8 –8.5 km per second in
the Mantle…
7.2 km per second in oceanic
crust...
3.5 km per second in continental
crust
Secondary Waves AKA S-Wave;
With these waves, the particle motion is
PERPENDICULAR to the direction of
energy transfer
a.
Transverse or Shear wave
b.
Will travel only through solid
c.
Travels 4 - 5 km per second
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d.
b.
Moves side to side like a snake
SURFACE WAVES:
move along the
surface of the earth only
1.
Surface Waves
AKA L-Wave
Travel through the crust of the earth and
attenuate (gradually disappear); Scientists
have found that attenuation occurs more
slowly in older rock (like the eastern US, but
more quickly in younger rock (western US)
a.
They’re two main types: Love
Waves and Raleigh Waves and
they will travel only through solid
b.
Travels less than 4 km per second
c.
Moves up and down- causes most
damage
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