Plate Tectonics
Lecture 11
What Are the Earths Major Geological Hazards?
´ Dynamic processes move matter within the earth and on its surface´ Cause volcanic eruptions,
earthquakes, tsunamis, erosion, and landslides
Plate Tectonics
´ Unified theory: Study the dynamic creation, movement, and destruction processes of plates
´ Plates: lithosphere fragments
´ Plates move in relation to each other at varied rates
´ No major tectonic movements within plates
´ Dynamic actions concentrated along plate boundaries
3 major types of plate boundaries
Divergent: plates moving apart and new lithosphere produced in mid-oceanic ridge
Convergent: plates collide, subduction and mountain building
Transform: two plates slide past one another
The Earth Beneath Your Feet Is Moving
Divergent Margins and the Red Sea
Figure 2.21Seafloor Spreading
Convergent Margins When plates collide
´Continent-Continent
´Ocean-Ocean
´Ocean-Continent
Transform Faults
Transform Margins along the Seafloor
San Andreas fault
Driving Mechanism´ What drives plate motion?
´ Old idea: plates are dragged atop a convectingmantle.
´Convection does occur; not the prime driving mechanism.
´ Modern thinking: two other forces drive plate motions. ´ Ridge-pushelevated MOR pushes lithosphere away.
´ Slab-pullgravity pulls a subducting plate downward.
Volcanoes Release Molten Rock from the Earths Interior
´ Volcano´Magma rising through the
lithosphere reaches the earths surface through a crack (fissure)
´Eruptionrelease of lava, hot ash, and gases into the environment
~1500 active volcanoes on Earth
400 erupted in the last century
~50 eruptions per year
Most activity concentrated along major plate boundaries
Impact risks depend on the type of volcano
Introduction
www.worldatlas.com
Viscosity of Magma and Explosiveness
Silicon-oxygen tetrahedron
Hot Spots
´ Volcanic centers with magma source from deep mantle, perhaps near the core-mantle boundary
´ A chain of volcanoes over a stationary hot spot
´ The bend of a seamount chain over a hot spot representing the change of plate motion
What are Earthquakes?
Faulting
´Occurs when rock breaks accompanied by displacement
´Occurs along zones of weakness in the crust, fault zones
´Fault lines´Begin as sudden ruptures, but
can result in large (hundreds of km) faults over millions of year
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Faulting
´Earthquakes´Vibration in Earth resulting from
sudden displacement along a fault
´Earthquake waves´Energy released by earthquakes
moves in several types of seismic waves that originate at the center of fault motion, the origin
´Ground above origin experiences strongest jolt, the epicenter
© 2011 Pearson Education, Inc.
Body Waves: P and S waves
´ Body waves´ P or primary waves
´fastest waves´travel through solids, liquids, or gases´compressional wave, material
movement is in the same direction as wave movement
´ S or secondary waves´slower than P waves´travel through solids only´shear waves – move material
perpendicular to wave movement
Surface Waves: R and L waves
´ Surface Waves´ Travel just below or along the grounds surface´ Slower than body waves; rolling and side-to-side
movement´ Especially damaging to buildings
Surface Waves: R and L waves
´ L-waves (Love waves)´Waves that intersect the land surface´Move the ground back and forth like a
writhing snake
´ R-waves (Rayleigh waves)´ Waves that intersect the land surface´ Particles underground follow a circular
path as the wave passes´ Cause the ground to ripple up and down
Where Do Earthquakes Occur and How Often?~80% of all earthquakes occur along the “Ring of Fire”
Earthquakes Are Geological Rock-and-Roll Events
´ Richter scale ´Insignificant: <4.0´Minor: 4.04.9´Damaging: 5.05.9´Destructive: 6.06.9´Major: 7.07.9´Great: >8.0
´ Largest recorded: 9.5 in Chile, 1960
Tsunamis
Earthquakes on the Ocean Floor Can Cause Tsunamis
´ Tsunami´Series of huge waves generated when ocean floor
suddenly rises or drops´Travels several hundred miles per hour
´Slows down as it approaches coastline´ December 2004Indian Ocean tsunami
´Magnitude 9.15 earthquake´Over 230,000 people lost their lives
´No warning system in place
Earthquakes on the Ocean Floor Can Cause Tsunamis
Where they Occur
(Setake and Atwater, 2007)
Plate Tectonics
What Are the Earths Major Geological Hazards?
Plate Tectonics
3 major types of plate boundaries�
The Earth Beneath Your Feet Is Moving
Slide Number 6
Figure 2.21
Convergent Margins �When plates collide
Transform Faults
Slide Number 10
Slide Number 11
Driving Mechanism
Volcanoes Release Molten Rock from the Earths Interior
Introduction
Slide Number 15
Viscosity of Magma and Explosiveness
Slide Number 17
Hot Spots
Slide Number 19
What are Earthquakes?
Faulting
Faulting
Body Waves: P and S waves
Surface Waves: R and L waves
Surface Waves: R and L waves
Where Do Earthquakes Occur and How Often?
Earthquakes Are Geological Rock-and-Roll Events
Tsunamis
Earthquakes on the Ocean Floor Can Cause Tsunamis
Earthquakes on the Ocean Floor Can Cause Tsunamis
Slide Number 31
Where they Occur
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