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
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
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
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