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Topic 12
The Dynamic Crust
Principle of Original Horizontality:
• The assumption that sedimentary rocks form in
horizontal layers.
Drawing:
• Then how do you explain this?
Evidence of Crustal Change
• Folding, faulting, tilting of rock strata
(layers)
• Drawings:
• Displaced rocks and fossils
• Volcanoes/ Earthquakes
“Continental Drift”- Alfred Wegener
Theory: the continents are sliding across
the Earths’ surface.
Evidence:
• Shape of the continents.
• Warm water fossils in Greenland.
• Similar rocks and fossils
• Similar mountain ranges
• Pangea- “All lands”
Pangea
Pillow Lavas
Plate Tectonics
Theory:
• Earth’s crust is made up of a variety of
plates that are moving.
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Divergent
Sea floor spreading
Alfred Wegener
Plate tectonics
Volcano
Convergent
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Mid ocean ridge
Transform Boundary
Mantle
Convection Currents
Trench
Subduction
Mid Ocean Ridge
•
Underwater mountain range that wraps
around the Earth
Evidence of Sea Floor Spreading
1. Age of rocks
2. Temperature of Rocks
3. Basalt Pillow lavas (igneous extrusive)
4. Paleomagnetism
Drawing:
Crustal plates move due to
convection currents in the
Earth’s mantle
(asthenosphere)!!!
Plate Boundaries
Oceanic Crust
• Thinner
• More dense
• basaltic
Vs. Continental
Crust
• Thicker
• Less dense
• granitic
Convergent Boundaries
1. Oceanic –
Continental
Drawing
Features
• E-quakes
• Volcanoes
• Trenches
• Mountains
Examples:
• South America
• Cascades
2. Oceanic – Oceanic
Drawing
Features
• E-quakes
• Volcanoes
• Trenches
• Mountains
Examples:
• Japan
• Aleutian Islands
(Alaska)
3. Continental –
Continental
Drawing
Features
• E-quakes
• Mountains
• Volcanoes (extinct)
Examples:
• Himalayas
Divergent Boundaries:
1. Mid Ocean Ridges
2. Rift Zones
Transform Boundary:
• Boundary where plates slide by each
other.
Drawing:
Example:
• San Andreas Fault
“Hot Spots”
• Regions of volcanic (magmatic) activity
usually away from plate edges.
Example:
• Hawaii
Earthquakes, volcanoes and
mountains are usually
associated with plate
boundaries.
BONUS:
• What is the relationship
between the distance a planet
is from the Sun and the
gravitational force between
the planet and the Sun?
Earthquakes
• The shock wave produced by the sudden
movement of rocks in the Earth’s crust.
Seismograph- instrument used to detect
and record earthquake waves.
Focus- point below the surface where the
earthquake originates.
Epicenter- point at the Earth’s surface
directly above the focus.
Seismic Waves
Primary Waves
Secondary Waves
• “P-Waves”
• Compressional waves
• “S-Waves”
• Transverse waves.
• Faster
• Travel through liquids
and solids
• Slower
• Travel through solids
only!
The difference between the P & S
wave arrival times can be used to
calculate the distance from the
epicenter.
To find the epicenter, one must find
the distance from at least 3 seismic
stations.
Earth’s Interior:
• See diagram p. 10 in the Earth Science
Reference Tables.
Evidence:
• Seismic Data
• Meteor Composition
• Earths Magnetic Field
• Moon Composition
Earthquake Damage
Depends on…
• Magnitude of the earthquake
• Distance from the epicenter
• Building structure
• Type of surface
Richter Scale vs. Mercalli Scale
Brain teaser
• A seismic station is located 5,200 km
away from the epicenter of an earthquake.
What will be the difference in the arrival
time between the P and S waves at this
station?
Earthquake Emergency Planning
Individual- “Drop, Cover and Hold”
• Drop down under strong object (desk,
table)
• Cover your eyes
• Hold onto the strong object you are under.
• Earthquake drills
• Have emergency supplies on hand.
Do not try to run out of buildings!!!
Earthquake Emergency Planning
Community
• Proper planning of building sites
• Proper building construction
• Retrofitting older buildings to make them
safer
Tsunami
• Large wavelength ocean wave produced
by disruption of the ocean floor.
Volcanoes
• A mountain composed of igneous extrusive
rock.
Violent Eruptions vs. Non-Violent Eruptions
Mt. St. Helens
Hawaii
BONUS:
• What was the name of the
scientist who developed the
Theory of Continental Drift?
BONUS:
• The epicenter of an earthquake is
4800 km away from a seismic
station. What is the difference in
arrival time of the P and S waves
at that station?
In Loving Memory of
Ebony
2006-2012