Plate Tectonics

1
Plate Tectonics

• Continental Drift

2
Historical Landmass Locations
3
Fossil Evidence Supporting Plate Tectonics
4
Developing the Theory

• (1) demonstration of the ruggedness and youth of
  the ocean floor
• (2) confirmation of repeated reversals of the
  Earth magnetic field in the geologic past
• (3) emergence of the seafloor-spreading
  hypothesis and associated recycling of oceanic
  crust and
• (4) precise documentation that the world's
  earthquake and volcanic activity is concentrated
  along oceanic trenches and submarine mountain
  ranges.

5
Developing the Theory (continued)

• (1) demonstration of the ruggedness and youth of
  the ocean floor.
• (See next slide)

6
Computer-generated topographic map of Mid-Oceanic
Ridge.
7
Mid-Ocean Ridge
8
Magnetic striping and polar reversals
9
Concentration of Earthquakes
10
Plate Motions

• There are four types of plate boundaries
• Divergent boundaries -- where new crust is
  generated as the plates pull away from each
  other.
• Convergent boundaries -- where crust is destroyed
  as one plate dives under another.
• Transform boundaries -- where crust is neither
  produced nor destroyed as the plates slide
  horizontally past each other.
• Plate boundary zones -- broad belts in which
  boundaries are not well defined and the effects
  of plate interaction are unclear.

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Types of Plate Boundaries
12
Divergent Boundaries
13
Mid-Atlantic Ridge Example
Red triangles denote active volcanoes
14
Aerial view of the area around Thingvellir,
Iceland, showing a fissure zone (in shadow) that
is the on-land exposure of the Mid-Atlantic
Ridge.
15
Divergent Boundary East Africa
Map of East Africa showing some of the
historically active volcanoes(red triangles) and
the Afar Triangle (shaded, center) -- a so-called
triple junction (or triple point), where three
plates are pulling away from one another
16
Summit Crater of 'Erta 'Ale (Ethiopia)
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Oldoinyo Lengai, erupts in 1966
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Convergent BoundariesOceanic-continental
convergence
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Convergent Boundaries (example)
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Oceanic-oceanic convergence
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Continental-continental convergence
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Continental-continental convergence
The collision between the Indian and Eurasian
plates has pushed up the Himalayas and the
Tibetan Plateau
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Continental-continental convergenceIndian
Eurasian Plates
24
The Himalayas Two Continents Collide The
6,000-km-plus journey of the India landmass
(Indian Plate) before its collision with Asia
(Eurasian Plate) about 40 to 50 million years
ago. India was once situated well south of the
Equator, near the continent of Australia.
25
Transform Boundaries
The Blanco, Mendocino, Murray, and Molokai
fracture zones are some of the many fracture
zones (transform faults) that scar the ocean
floor and offset ridges (see text). The San
Andreas is one of the few transform faults
exposed on land.
26
San Andreas fault
Aerial view of the San Andreas fault slicing
through the Carrizo Plain in the Temblor Range
east of the city of San Luis Obispo.
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Plate-boundary Zones
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Rates of Motion

• The Arctic Ridge has the slowest rate (less than
  2.5 cm/yr)
• The East Pacific Rise near Easter Island, in the
  South Pacific about 3,400 km west of Chile, has
  the fastest rate (more than 15 cm/yr).

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Hotspots Mantle Thermal Plumes
30
Prominent Thermal Hotspots
31
The Long Trail of the Hawaiian Hotspot
Map of part of the Pacific basin showing the
volcanic trail of the Hawaiian hotspot--
6,000-km-long Hawaiian Ridge-Emperor Seamounts
chain.
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Plate Tectonics People

• Natural hazards
• Earthquakes
• Volcanic eruptions
• Tsunamis
• Natural resources
• Fertile soils
• Ore deposits
• Fossil fuels
• Geothermal energy

33
Earthquakes
Aerial view, looking north toward San Francisco,
of Crystal Springs Reservoir, which follows the
San Andreas fault zone.
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Earthquakes (continued)
Map of the San Andreas and a few of the other
faults in California, segments of which display
different behavior locked or creeping
35
Fault Creeping
Left Creeping along the Calaveras fault has bent
the retaining wall and offset the sidewalk along
5th Street in Hollister, California (about 75 km
south-southeast of San Jose). Right Close-up of
the offset of the curb.
36
Earthquakes Volcanoes

• Christopherson TextChapter 12 pp
  375-end-of-chapter

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What Causes Earthquakes?
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Epicenter and Focus

• Focus 
• Location within the earth where fault rupture
  actually occurs 
• Epicenter 
• Location on the surface above the focus

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Types of Faults

• Faults are classified on the basis of the kind of
  motion that occurs on them
• Joints - no movement
• Strike-slip - horizontal motion (wrench faults)

40
Types of Faults

• Joints - No Movement
• Strike-Slip - Horizontal Motion (Wrench Faults)

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Joints - No Movement
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Left Lateral Strike Slip
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Right Lateral Strike Slip
San Andreas 21 feet in 1906
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Dip-Slip - Vertical MotionNormal Fault
(Extension)
Alaska, 1964 - up to 150 Ft
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Reverse or Thrust Fault (compression)
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Eastern North America Earthquakes 1534-1994
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U.S. Earthquakes, 1973-2002
48
Seismic Risk Level Maps for the U.S.Probable
ground acceleration in 50 years. Blue small,
red large
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Seismic Risk Level Maps for the U.S.Probability
of Damage in 100 Years. Blue Negligible, Green
Low, Red High.
50
M 7.9 Earthquake on November 3, 2002

• The largest earthquake known to occur in the
  world this year struck central Alaska on Sunday,
  November 3. The epicenter of the Nov. 3 temblor
  was located approximately 75 miles south of
  Fairbanks and 176 miles north of Anchorage. It
  struck at 112 PM local time, causing countless
  landslides and road closures, but minimal
  structural damage and amazingly few injuries and
  no deaths.

51
M 7.9 Earthquake on November 3, 2002

• Overall, the geologists found that measurable
  scarps indicate that the north side of the Denali
  fault moved to the east and vertically up
  relative to the south. Maximum offsets on the
  Denali fault were 22 feet at the Tok Highway
  cutoff, a road that goes from Tok to Glenallen
  and intersects with the Alaska Highway, and were
  6.5 feet on the Totschunda fault.
• This earthquake is one of the largest ever
  recorded on U.S. soil and the largest seismic
  event ever recorded on the Denali fault system.

52
Denali Fault Earthquake
53
Rock Avalanches Across Black Rapids Glacier
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Alaska Earthquake Pictures Taken by Local Resident
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Alaska Earthquake Pictures Taken by Local Resident
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Alaska Earthquake Pictures Taken by Local Resident
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Alaska Earthquake Pictures Taken by Local Resident
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Alaskan Pipeline
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Northway Road - 4th of November 2002
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Road Offset, Richardson Hwy
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Volcanoes
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Two expressions of volcanic activity.
63
Volcanic fountaining in Hawaii.
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Kilauea landscape.
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Mt.Etna, Sicily July 2001
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Mt.Etna, Sicily July 2001
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Mt.Etna, Sicily July 2001
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Mt.Etna, Sicily July 2001
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Mt.Etna, Sicily July 2001
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Mt.Etna, Sicily July 2001
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Mt.Etna, Sicily July 2001