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Unit
3: The Dynamic Crust
Earthquakes
(see
http://www.zephryus.demon.co.uk/geography/resources/earth/cause.html
) |
An earthquake is any shaking or vibration of the earth's crust.
They occur where stress builds at a zone of weakness or at a break in the earth's crust
called a fault . Seismic
waves are generated in all directions from the point on the fault that moved.
This point is called the focus. The point directly above the focus on the earth's
surface is called the epicenter. This is what you see
plotted on a map to represent the location of the earthquake.
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| There are
2 main
causes of earthquakes: |
1)
explosive volcanic eruptions- they are
very common in areas of volcanic activity where they either proceed or accompany
eruptions.
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2) triggered by Tectonic activity
associated with plate margins and fault(MOST EQ’s!).
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EARTHQUAKE ENERGY |
| P
waves: (primary)=FASTEST |
S-waves: SECONDary |
L-waves: Longitudinal (surface)= most damage!
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Earthquake
Seismogram
You can use the time difference to
determine the distance to the earthquake epicenter.
You must TRIANGULATE to determine the location of the epicenter. |
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| To find the epicenter locate three seismic stations and draw circles, wherever
the three circles intersect is the epicenter of the earthquake.
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Crustal
Changes:
folding, faulting and uplift can be the result of tectonic and earthquake
activity |
 SYNCLINE:
Upward folding of rock layers with
youngest in core of fold. |
 ANTICLINE:
Downward folding with oldest layers in
core of fold. |
 HORST
& GRABEN: uplifted and downthrust blocks of crust bounded by
faults on either side. |
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FAULTS:
this is a normal fault, in which the hanging (look near top)
wall appears to have moved downward relative to the foot (sticking out
near bottom) |
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Shadow
Zones & Earth’s Makup:
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Plate
Tectonics: From
Continental Drift to Seafloor Spreading |
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Evidence for Pangea-
*
*
*
* |
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| Continental
versus Oceanic Crust:
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| Alfred
Wegener: Ideas and Controversy-
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Plate Tectonics is the study of the formation and movements of the
lithospheric plates. However, many other theories were made on how the continents got the
way they are. Robert Wegner’s theory of Continental Drift, and sea-floor
spreading were just some of the theories leading up to this theory of Plate Tectonics |
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PLATE BOUNDARIES: |
| Divergent boundaries
--
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| Convergent
boundaries
--
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| Transform
boundaries
--
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What
is the Evidence for Plate Tectonics? |
What is the driving
force? |
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Seafloor Spreading:
Paleomagnetic reversals as
evidence... |
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Problems?
How can HOT SPOTS be
explained? Rising
Adirondacks? Earthquakes in CT? |
Try these links for extra information
Geology Labs online-Virtual Seismologist http://vcourseware.calstatela.edu
Ask a geologist at USGS.gov http://walrus.wr.usgs.gov/docs/ask-a-ge.html
Eruptions of Mt. St. Helens http://pubs.usgs.gov/publications/msh/title.html
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