Age of Ocean Crust
Young at mid-ocean ridges
Old at ocean margins (edges)
So … where is ocean crust created?
And … where is it destroyed?
Plate Tectonics I
At both areas,
there should be
earthquakes.
Earth’s Ever-Changing Lithosphere
Unifying continental drift and
seafloor spreading
Seismicity the frequency, magnitude,
and intensity of earthquakes
Earthquakes – produce seismic waves
First, a bit of a geological aside …
Scientists deduced the interior structure of Earth by using the
travel time, arrival location, and refraction of seismic waves
P-waves (“primary” – arrive 1st)
Quake !
• compressional force
• back-and-forth motion
Tectonic terminology
Next, a bit of a
review/clarification …
S-waves (“secondary” – arrive 2nd)
Continental
Crust
crust & mantle
vs.
lithosphere & asthenosphere
• shear between layers
• up-and-down motion
• cannot travel through liquid
Tectonic plates are
pieces of lithosphere,
comprised of the rigid
crust and the rigid part
of the upper mantle.
Tectonic plates float
and move on top of the
ductile part of the upper
mantle called the
asthenosphere.
Oceanic
Crust
sea level
Lithosphere
uppermost Mantle 200
(rigid)
400
• travel through both solids and liquids
Oceanic
Crust
km
Asthenosphere
= part of upper Mantle
600
800
Mantle (rigid)
1000
Lithosphere
rigid outer layer of the
Earth that includes the
Crust (Continental Crust
and Oceanic Crust)
and the
uppermost Mantle
Asthenosphere
low strength, ductile part
of upper Mantle
700 km
Mantle
2900 km
Liquid
Outer
Core
5200 km
Solid
Inner
Core
Radius of the Earth
= 6370 km
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Tectonic terminology
Another view of the lithosphere / asthenosphere
Seismicity around the world
Earthquake locations helped lead to Plate Tectonics idea
Notice the asthenosphere can deform and flow …
whereas the lithosphere maintains its shape.
This allows the rigid lithosphere to move atop the
weak rock of the asthenosphere.
Note difference between Atlantic and Pacific seismicity
Note Himalayan-Mediterranean belt
HimalayanMediterranean
Atlantic
Pacific
Plate Tectonics
Earth’s lithosphere consists of tectonic plates, 7 major
plates (most of which contain a major continents plus
ocean crust) and 7 minor (or intermediate) plates.
major plates: North American, South American, African,
Eurasian, Pacific, Australian-Indian, and Antarctic
minor plates: Juan de Fuca, Caribbean, Arabian, Cocos,
Nazca, Scotia, Philippine
Plate boundaries have their faults
3 types of faults (and plate boundaries)
normal – result from tension
(divergent plate boundaries)
reverse – result from
compression
(convergent plate boundaries)
transform – result from sliding
(translational plate boundaries)
Plates move as coherent units relative to other plates.
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Plate boundaries – 3 types
convergent
Divergent
spreading ridges
(Mid-Atlantic Ridge)
divergent
Convergent
continent-continent collision
(Himalayas, Alps)
subduction zones
translational
ocean-ocean
(Mariana Trench)
ocean-continent
(Peru-Chile Trench)
Translational
(San Andreas Fault)
Divergent
Convergent
Translational
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