Transcript Plate Tectonics - City University of New York

Plate Tectonics
Continental Drift
Historical
Landmass
Locations
Fossil Evidence Supporting Plate
Tectonics
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.
Developing the Theory (continued)
• (1) demonstration of the ruggedness and youth of
the ocean floor.
•
(See next slide)
Computer-generated topographic map of
Mid-Oceanic Ridge.
Mid-Ocean Ridge
Magnetic striping and polar reversals
Concentration of Earthquakes
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.
Types of Plate Boundaries
Divergent
Boundaries
Mid-Atlantic Ridge Example
Red triangles denote
active volcanoes
Aerial view of the area
around Thingvellir,
Iceland, showing a
fissure zone (in shadow)
that is the on-land
exposure of the MidAtlantic Ridge.
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
Summit Crater of 'Erta 'Ale
(Ethiopia)
Oldoinyo Lengai, erupts in 1966
Convergent Boundaries
Oceanic-continental convergence
Convergent Boundaries (example)
Oceanic-oceanic convergence
Continental-continental
convergence
Continental-continental convergence
The collision between the
Indian and Eurasian plates
has pushed up the
Himalayas and the Tibetan
Plateau
Continental-continental convergence
Indian – Eurasian Plates
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.
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.
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.
Plate-boundary Zones
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).
Hotspots: Mantle Thermal Plumes
Prominent Thermal Hotspots
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.
Plate Tectonics & People
• Natural hazards
– Earthquakes
– Volcanic eruptions
– Tsunamis
• Natural resources
–
–
–
–
Fertile soils
Ore deposits
Fossil fuels
Geothermal energy
Earthquakes
Aerial view, looking
north toward San
Francisco, of Crystal
Springs Reservoir, which
follows the San Andreas
fault zone.
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
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.
Earthquakes & Volcanoes
• Christopherson Text
Chapter 12 pp 375-end-of-chapter
What Causes Earthquakes?
Epicenter and Focus
• Focus
– Location within the earth where fault rupture
actually occurs
• Epicenter
– Location on the surface above the focus
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)
Types of Faults
•Joints - No Movement
•Strike-Slip - Horizontal
Motion (Wrench Faults)
Joints - No Movement
Left Lateral Strike Slip
Right Lateral Strike Slip
San Andreas
21 feet in 1906
Dip-Slip - Vertical Motion
Normal Fault (Extension)
Alaska, 1964 - up to 150 Ft
Reverse or Thrust Fault (compression)
Eastern North America
Earthquakes 1534-1994
U.S. Earthquakes, 1973-2002
Seismic Risk Level Maps for the U.S.
Probable ground acceleration in 50 years.
Blue = small, red = large
Seismic Risk Level Maps for the U.S.
Probability of Damage in 100 Years.
Blue = Negligible, Green = Low, Red = High.
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 1:12 PM local time, causing countless
landslides and road closures, but minimal
structural damage and amazingly few injuries and
no deaths.
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.
Denali Fault Earthquake
Rock Avalanches Across Black
Rapids Glacier
Alaska Earthquake Pictures
Taken by Local Resident
Alaska Earthquake Pictures
Taken by Local Resident
Alaska Earthquake Pictures
Taken by Local Resident
Alaska Earthquake Pictures
Taken by Local Resident
Alaskan Pipeline
Northway
Road - 4th of
November
2002
Road Offset, Richardson Hwy
Volcanoes
Two expressions of volcanic activity.
Volcanic fountaining in Hawaii.
Kilauea landscape.
Mt.Etna, Sicily – July 2001
Mt.Etna, Sicily – July 2001
Mt.Etna, Sicily – July 2001
Mt.Etna, Sicily – July 2001
Mt.Etna, Sicily
July 2001
Mt.Etna, Sicily – July 2001
Mt.Etna, Sicily – July 2001