10’largestearthquakes’in’the’world’...Pangea – a “supercontinent” Motion of...
Transcript of 10’largestearthquakes’in’the’world’...Pangea – a “supercontinent” Motion of...
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M.Roy, UNM, EPS 101, Lecture 18-‐19 1
10 largest earthquakes in the world
hCp://wwwneic.cr.usgs.gov/neis/eqlists/10maps_world.html
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M.Roy, UNM, EPS 101, Lecture 18-‐19 2
Where do earthquakes occur?
Epicentral distribuNon (magnitude > 5) 1980-‐1990
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Plate tectonics and continental drift!Pangea – a “supercontinent”
Motion of continents on the Earth’s surface – for example, evidence from the “fit” of the continental shelves of south America and Africa! -Alfred Wegener, 1914
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Lithospheric plates on Earth
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Plate boundaries – 3 types
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What causes plate moNon?
• CirculaNon within the mantle – mantle rocks flow very slowly, over millions of years!
T-6
• This flow allows the Earth to lose heat – primary heat loss mechanism – the cooling from the nebula continues today!
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Plate tectonics and modern evidence for it - I!
I. Apparent polar wander (APW) of the conNnents.
What does this mean??
First, recall that Earth has a magneNc field
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The inclinaNon of a compass needle changes with laNtude
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Some rocks have magneNc minerals that are like liCle compasses
As an igneous rock cools, the magneNc minerals all align with the Earth’s magneNc field and then, once cooled, the alignment cannot change!!!
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Apparent polar wander - Rocks of different ages on the same continent point to different positions of the magnetic north pole!
- Magnetic poles do move slightly, but most of this is due to the rocks (on continents) moving!
- Rocks on different continents give different apparent polar wander paths –even if they are of the same ages! Thus, the continents have drifted!
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Plate tectonics and modern evidence for it - II!
II. Sea Floor Spreading.
What does this mean??
Global mid-‐ocean ridge system
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Age of the ocean floor
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Ridge processes
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MagneNc stripes on the seafloor
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Evidence for sea-‐floor spreading
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Seafloor Spreading and Plate Tectonics
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Mid-ocean ridges and continental
rifts: divergent
plate boundaries!
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Divergent – ConNnental riaing mid-‐ocean ridge!
We live in a continental rift – the Rio Grande rift
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ConNnental rias that are in the process of forming oceans!
Gulf of California, Mexico
Red Sea
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Mantle convecNon – whole vs. layered
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Seismic waves are used to
image subducted oceanic slabs! – favor whole mantle
convecNon
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Hotspots
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Hawaii Shift in Plate
Direction
Hawaii (AcNve)
Oahu (2-‐3 Myr)
Midway (25 Myr)
What direcNon is plate currently moving?
When was shia?
What direcNon was plate moving 50 Myr ago??
43 Myr
60 Myr
A
B
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