Download 2-Unit4Part2 EarthsInteriors

The Structure of the
Earth
The Earth’s Interior:
Methodology
Earth’s Interior
• How do we know what it is like today?
– Drilling
• Most drilling includes the upper 7 km of crust
• Deepest well: Soviet – 12 km deep
– 5 yrs, 7 km; 9 yrs, 5 km; then it got stuck
– Cost $100 million dollars
– Temperature 190oC
–
–
–
–
Volcanic Activity
Laboratory experiments
Meteorites
Seismic Wave studies
• http://www.youtube.com/watch?v=fiW4
gnaqCv4
Meteorites: Evidence about the Interior
• Meteorites
– Fragments of asteroids and small early planets
(planetesimals) that broke up as a result of collision with
other solid bodies
• Composition of Meteorites
– Divisions
• 1. Iron-nickel meteorites
– From core of original bodies??
• 2. Stony meteorites
– Original body area like our mantle
• 3. Stony-iron meteorites
– 3 subclasses:
» Chrondrites
» carbonaceous chondrites
» achondrites
– From the cores and mantle of asteroids & planetismals
Iron-nickel meteorites
90% iron
• 9% nickel
•
.
Stony Meteorite
Stony-iron meteorites
•
http://www.meteorites-for-sale.com/meteorites-forsale.html?gclid=CLaAsLOl9b0CFYdFMgod4xIAEA
• http://webecoist.momtastic.com/2010/01/12/heavy-hittersearths-most-amazing-meteor-craters/
Seismology: Evidence of the Earth’s
Interior
• Seismology
– The scientific study of earthquake
– The key to understanding the Earth’s
interior
Seismic Waves
• What are they?
– Vibrations in the body of the Earth
• How are they generated?
– Naturally
• Earthquakes
• Volcanoes
• Impacts
– Artificially
• Explosions
• Mechanical devices
Seismic Waves: Measuring
• Seismograph
– Thousands of stations are set up
worldwide
– Used to locate earthquake
– Simple pendulum
• When the ground shakes, the
base and frame of the instrument
move with it
• Inertia keeps the pendulum in
place
• It will then appear to move;
relative to the shaking ground
• As it moves, it records the
pendulum displacement
• The tracing is called a
seismogram
– Networks of seismograph
stations are used to determine the
location of the earthquake
• Seismology and the Science of
Earthquakes – Waves – Magnitude –
and the Richter Scale
• (3:22 minutes)
Seismic Waves: Terms
• Earthquake
– Release of stress build up along a fault
– Slipping and moving of rocks along a fault
• Focus
– The origin of seismic waves
– The energy of seismic waves is released from this point
• Epicenter
– The point on the earth’s surface directly above the focus
• Fault
– Crack or break in the earth’s crust
– Surface along which rocks move
• Waves:
– P waves
– S waves
– L waves
Seismic Waves
• 3 Main Types released by Earthquakes:
1. P-waves (Primary / Compression waves)
• Longitudinal / compressional wave
– Alternately push (compress) and pull (dilate) the
rocks through which they pass
» Squeezes and stretches the material in the same
direction
– Generated by the Focus
• Fastest of the waves
• Propagates through solids, liquids and gases
2. S-waves (Secondary / Side-to-side
waves)
• Transverse waves
– Generated by the Focus
• Slower wave
• Moves material at right angles to the wave
direction
• Propagate only solids
Animation of P and S Waves
• http://www.classzone.com/books/earth
_science/terc/content/investigations/es
0402/es0402page05.cfm
• http://www.classzone.com/books/earth
_science/terc/content/visualizations/es
1002/es1002page01.cfm?chapter_no=
visualization
3. L-waves (Long waves or Love Waves)
• Surface waves that cause horizontal shearing of
the ground
– Travel on the surface of the earth and shake
rocks
sideways as they move across the
surface
– Generated by the epicenter
– Particles travel in a rolling motion
– Note:
• Surface waves cause the most damage
• Not used to determine Earth’s interior
Locating The Epicenter
• P and S waves travel at different rates
– This helps determine the distance to the
epicenter
• P waves will always arrive at a seismic
station first
– The distance of the P wave ahead of the S
wave depends on how far away the
earthquake is
• Key: The further away the epicenter,
the wider the gap between the P and S
waves.
How is an Earthquake’s Epicenter Located?
Seismic wave behavior
– P waves arrive first, then S waves, then L and R
– Average speeds for all these waves is known
– After an earthquake, the difference in arrival times at a seismograph
station can be used to calculate the distance from the seismograph to
the epicenter.
How is an Earthquake’s Epicenter Located?
Time-distance graph
showing the average
travel times for Pand S-waves. The
farther away a
seismograph is from
the focus of an
earthquake, the
longer the interval
between the arrivals
of the P- and Swaves
How is an Earthquake’s
Epicenter Located?
•
•
•
Three seismograph stations
are needed to locate the
epicenter of an earthquake
A circle where the radius
equals the distance to the
epicenter is drawn
The intersection of the
circles locates the epicenter
Earthquakes: Measuring Severity
• There are two scales used:
– Richter Scale
– Modified Mercalli Intensity Scale
Earthquakes: Measuring Severity
• Richter Scale
– Measures the amount of energy (magnitude) released
by an earthquake
– Allows for easier comparison of earthquake
magnitudes regardless of location
– Logarithmic
• Measurements range from 1 to over 9
• Meaning a 6 is 10 times more powerful than a 5
• The earthquake with the biggest recorded
Magnitude was the Great Chilean Earthquake. It
had a magnitude of 9.5 (approximately 9.5 on the
Richter scale) and occurred in 1960.
Approximately 6,000 people died because of the
earthquake. .
Descriptor
Richter Magnitude
number
Damage caused by the earthquake
Frequency of occurrence
Micro
Less than 2.0
Micro (very small) earthquakes, people cannot feel these.
About 8,000 each day
Very minor
2.0-2.9
People do not feel these, but seismographs are able to detect
them.
About 1,000 per day
Minor
3.0-3.9
People often feel these, but they rarely cause damage.
About 49,000 each year
Light
4.0-4.9
Objects inside houses are disturbed, causing noise. Nothing is
damaged.
About 6,200 each year
Moderate
5.0-5.9
Buildings that are not built well may be damaged. Light
objects inside a house may be moved.
About 800 per year
Strong
6.0-6.9
Moderately powerful. May cause a lot of damage in a larger
area.
About 120 per year
Major
7.0-7.9
Can damage things seriously over larger areas.
About 18 per year
Great
8.0-9.9
Massive damage is caused. Heavy objects are thrown into the
air and cracks appear on the ground, as well as visible
shockwaves. Overhead highways may be destroyed, and
buildings are toppled.
About 1 per 20 years
Meteoric
10.0+
There are no records of anything of this size. The vibration is
about the same as that of a 20km meteor.
Unknown
Earthquakes: Measuring Severity
• Modified Mercalli Intensity Scale
– Measures the severity of the earthquake
by observing the damage caused
• I – felt by only a few people under very
special circumstances
• II – felt by only a few people at rest,
especially on the upper
floors of
buildings
• Continues ….
• X - Most structures destroyed; rails bend;
landslides occur; water splashes over banks
• XII – Damage total; waves on ground surface;
objects thrown in air
•
Ninety percent
of the world's
earthquakes
occur in specific
areas that are
the boundaries
of the Earth's
major crustal
plates. Shown
on the map are
the epicenter
locations of
earthquakes of
magnitude 4.5 or
greater that
occurred from
1978 through
1987.
• http://earthquake.usgs.gov/earthquake
s/
Earthquake
• http://earthquake.usgs.gov/eqcenter/
• Predicting Earthquakes
• Video 2 minutes
• Earthquakes
• Video 3 minutes
Earthquake Assignment
• Handout
– Choose a time frame
– Using the website provided, research 10
earthquakes in the given time frame
– Number the Earthquakes from 1 to 10
and place the numbered location on the
world map
– Answer the questions
– Total value: 48 marks
Volcanoes: Evidence of the Earth’s
Interior
• Referred to as “Windows into the
Earth’s Interior.” Why?
• Volcanoes erupt material that is
tens to hundreds of kilometers into
the Earth
– Deepest rock samples of the Earth’s
interior are volcanic rock
Volcano Assignment
• Visit the links identified on the
assignment and answer the questions.
• Total value: 65 marks
Bill Nye Video: Volcanoes
• 24 minutes
• Complete Video worksheet and hand
in for marks.
Importance of Earth Hot Interior
• Seismic activity – earthquake, volcano
• Magnetic field (Geomagnetism)
– Generated by the movements of the molten iron
and nickel layer in the outer core
– Convection current in this electrically conducting
fluid act as a Dynamo*
• Fluid acts to generate and maintain the magnetic field
• * Dynamo theory
– Process through which motion of a conductive body in the
presence of a magnetic field acts to regenerate the magnetic
field
– Note: Without this Dynamo effect, the magnetic
field would die out within 10 000 years
Importance of Earth Hot Interior
• Interior heat powers convection
current of the asthenosphere which
in turn allows the lithosphere to
move (plates moving)
– Result:
•
•
•
•
formation of mountain ranges
deep sea trenches
Volcanic belts
Earthquake zones
• May be linked to long-term climatic
changes