Transcript Forces In The Earths Crust

Forces In The Earths Crust
Crust: the thin outermost layer of
the earth.
Continental crust is relatively
thick and mostly very old.
Oceanic crust is relatively thin and
is always geologically very young.
Forces In The Earths Crust
Forces In The Earths Crust
The continents we live on are parts of
moving plates.
Most of the action takes place where
plates meet.
Plates may collide, pull apart, or scrape past
each other.
Forces In The Earths Crust
The plates are
technically called
lithospheric plates.
Forces In The Earths Crust
Lithospheric Plates:
•Move very slowly 10-20 cm per year
•Stress and strain produced by moving plates
builds up in the Earth's rocky crust,
resulting in tremendous forces.
Forces In The Earths Crust
Types of Forces:
Tension force- a force that tends to pull
material apart
Compression force- a force that tends to
push material together
Shear force- a force that tends to make two
masses of material slide past each other
Forces In The Earths Crust
http://scign.jpl.nasa.gov/learn/plate5.htm
Forces In The Earths Crust
Forces can cause the rocks in the
the earths crust to:
•Fold
•Fracture (break)
•Slip along the fracture surfaces
Forces In The Earths Crust
Fault: a fracture
surface along
which rock slips
Forces In The Earths Crust
Basic Types of Faults
•Normal faults
•Reverse faults
•Strike-slip fault
Forces In The Earths Crust
Normal Fault
•Formed by tension
forces
•Rock above the fault
plane slides down,
relative to the rock
below the fault plane
Forces In The Earths Crust
Reverse Fault
•Formed by compression
forces
•Rock above the fault
plane slides upward,
relative to the rock
below the fault plane
Forces In The Earths Crust
Strike-Slip Fault
•Formed by horizontal
shear forces
•Rock on either side of
the fault plane slides
past each other
horizontally
Strike-Slip Fault
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Forces In The Earths Crust
Hanging Wall & Foot Wall
•Foot Wall: in this picture,
the block farthest to the
right (shaped like a foot)
•Hanging Wall: the block on
the other side, resting or
hanging on the footwall
Forces In The Earths Crust
Fault Scarp:
•The fault has ruptured the
Earth surface
•Fault-generated cliff is
called a fault scarp
Forces In The Earths Crust
http://scign.jpl.nasa.gov/learn/plate6.htm
http://www.iris.washington.edu/gifs/animations/faults.htm
http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/tecton
ics_landforms/faulting_p2.html
http://highered.mcgrawhill.com/sites/0072402466/student_view0/chapter15/animations_
and_movies.html#
Forces In The Earths Crust
Folds are usually formed when rocks are squeezed
together by compressive forces.
An excellent example
of a folded mountain
belt is the Atlas
Mountain system of
northwest Africa.
Source: NASA Goddard Space Flight Center
Forces In The Earths Crust
Folding vs. Faulting
Temperature and time determine whether the rock
becomes a fold or a fault.
•Rocks in the upper parts of the earths crust have
lower temperatures.
•Tend to deform by fracturing to form faults
•Rocks in lower parts of the earths crust have
higher temperatures.
•Tend to deform by changing shape continuously
to form folds
Forces In The Earths Crust
Folding vs. Faulting
Temperature and time determine whether the rock
becomes a fold or a fault.
•If a force builds up very fast rocks are more likely
to fracture.
•If a force builds up very slowly the rock is more
likely to change shape without breaking.
Forces In The Earths Crust
http://www.wwnorton.com/college/geo/egeo/flash/9_1.swf
http://highered.mcgrawhill.com/sites/0072402466/student_view0/chapter15/animations_an
d_movies.html#
Forces In The Earths Crust
Folds
Source: www.geology-israel.co.il/WEB%20PAGE/folds-1.jpg
Forces In The Earths Crust
Folds- Slide Show
University of North Dakota: Geology 101
http://www.und.nodak.edu/instruct/mineral/101intro/s
lides/folds/slide1.htm
Forces In The Earths Crust
Folds
Folds that are concave
upward are called
synclines.
Syncline
Folds that are convex
upward are called
anticlines.
Anticline
Source: Georgia Perimeter College Geology 101
http://www.gpc.edu/~pgore/geology/geo101/folds.htm
Forces In The Earths Crust
Credits
•United States Geological Survey
http://geology.wr.usgs.gov/docs/parks/deform/gfaults.html
Earth Comm- 5 Unit Edition
Activity #5 Structural Geology and Your Community