Download Chapter 5 Notes

Earthquake
Notes
Crustal Deformation
REVIEW:
So far we have found that
convection currents cause several
things to happen.
1. Continental movements
2. Earthquakes
3. Volcanoes
4. Mountains
ISOSTATIC
ADJUSTMENT up
and down movements
of crust.
This adjusts for uplift
and weathering of
mountains.
These movements
cause…
STRESS ON THE ROCKS!!!!
Stress - the amount of force
placed on the rocks, also called
STRAIN.
• There are 3 TYPES OF STRESS
–COMPRESSION Pushing
together of rocks
–TENSION Pulling apart of
rocks
–SHEARING Lateral (side to
side) tearing of rocks
–With Continental Movements comes
breaks and folds in the rocks of the
continents.
3 TYPES OF FOLDS
• Limbs - sides of the fold or rock
layers before and following a fold.
1. ANTICLINE - an upward fold in
rock layers where oldest rock layer
is in the center of the fold. Limbs
fold down, it forms a ridge (hill)
3 TYPES OF FOLDS
2. SYNCLINE_ a syncline is a
downward fold in the rock layers
where youngest rocks are in the
center. Limbs fold up, it forms a
valley.
3 TYPES OF FOLDS
3. MONOCLINE_ slight fold in one area but
both limbs remain horizontal
4. Dip (steepness) of the limbs reflects the
intensity of the fold.
5. Strike is the compass direction of the fold
of the rock layer.
6. Folding can be so severe the rock layers
are overturned or upside down.
2 TYPES OF BREAKS IN ROCK
LAYERS:
• FRACTURE_ Break in rock layers
•
•
where no movement has occurred.
FAULT_ Break in rock layers where
movement has occurred or is
currently happening. There are
several in Kentucky
Movements along faults account for
80% of all earthquakes, the other
20% from plate boundaries.
2 SIDES TO EVERY FAULT:
• Look at it this way, imagine you are
standing on a fault:
• HANGING WALL- surface of rock directly
above the fault plane. (over your head)
• FOOTWALL- surface of rock directly below
the fault plane. (your are feet on it)
UNC geologists illustrating the concept of footwall and hanging wall at a small
fault near Las Vegas, Nevada. Their feet are on the footwall, and the hanging wall
is hanging over their heads. This is a small normal fault. Grooves and scratches
on the fault plane run down the dip of the plane.
MAJOR TYPES OF FAULTS
• NORMAL FAULT- occurs when hanging
wall moves down. You think it is NORMAL
because gravity would act on it so it drops
down
• This is caused by a Tension force on this
type of fault.
• Convections cells pulling on rocks of crust
cause tension force.
MAJOR TYPES OF FAULTS
• REVERSE FAULT- hanging wall moves up
due to compression forces, this moves
opposite of the normal fault.
• Convections cells pushing on rocks of
crust cause the compression force.
MAJOR TYPES OF FAULTS
• THRUST FAULT- Special kind of reverse
fault, the angle of the fault plane is very
low, almost horizontal.
• STRIKE-SLIP FAULT -( Transform fault)
The rocks move horizontally in relation
to each other by
• Most common at transform boundaries
like: San Andreas Fault in California.
MOUNTAINS FORM IN 3 WAYS
• CONTINENTAL VS OCEANIC PLATES_
Produces much crustal deformation. High
mountains produced, mostly volcanic
because the ocean plate is subducted
beneath the continent.
– Ex Cascade Range.
MOUNTAINS FORM IN 3 WAYS
• OCEANIC VS OCEANIC_ Produces little
crustal deformation. Large volcanic
mountain islands form. Peaks of these
volcanic mountains reach from ocean
floor to surface.
– Ex. Mariana Islands in North Pacific form.
MOUNTAINS FORM IN 3 WAYS
• CONTINENTAL VS CONTINENTAL_
Produces intense crustal deformation
with immense mountain ranges of folded
and faulted mountains.
– Ex Himalayas.
4 KINDS OF MOUNTAINS
• FOLDED_ Highest mountains in the world,
rocks squeezed together like an accordion.
–
Ex. Appalachian
• PLATEAU_ Large areas of flat-topped rocks
high above sea level. Formed by thick
horizontal layers of rock slowly uplifted. Most
are next to mountain ranges.
–
Ex. Tibetan Plateau
4 KINDS OF MOUNTAINS
• FAULT-BLOCK MOUNTAINS_ Sections of
crust broken into large blocks and
shifted, up, down, or over other sections.
– Ex Nevada, Arizona, Utah…
• GRABENS_ These develop when steep
faults break crust into blocks, then
block(s) slips downward along normal
faults.
– Ex Death Valley Ca.
4 KINDS OF MOUNTAINS
• VOLCANIC_ Molten rock erupts onto surface,
on land, ocean floor. Some of largest are
along mid-ocean ridges. Others over hot
spots.
– Ex Azores and Hawaiian islands.
• DOME_ Unusual, molten rock rises through
crust, pushes up rock layers, never melts
through to surface. Eventually, cools and
hardens, erosion removes rocks over it
leaving separate high peaks.
– Ex Black Hills of South Dakota, Adirondack
Mountains of New York State.
Strike-slip fault
• The rocky blocks on either side of strike-slip
faults, scrape along side-by-side, no vertical
movement means no hanging or foot wall.
Thrust fault along
Interstate-70,
Silverthorne --Younger rocks on
the very bottom of
this picture have
been thrust under
older rocks and
pushed west (left)
for several miles.
• The fault line ascends slowly from the lower right edge
of the picture to beyond the center where some folding
of the layers at the fault contact can be seen.
Reverse Fault
• Along a reverse fault one rocky block, the
hanging wall, is pushed up relative to rock
on the other side.
Normal Fault
• A normal fault drops rock on one side of the
fault down relative to the other side. Take a
look at the side that shows the fault and
arrows indicating movement
• Fracture
• Note the
number of
fractures
these are
small
others can
be huge.
• Huge faults visible in the
side of this canyon. This
faulting occurred over
20,000,000 years.
This is what faulting can do
to the surface of the earth
during an earthquake. This
faulting occurred during 1
earthquake.
Known Major KY Faults
FIGURE 16.--. Solid lines indicate fault traces.
Tension VS undeformed rock strata
Back to Normal
Shearing VS undeformed rock strata
Compression verses undeformed rock strata
This Anticline is 500 feet thick.
This Syncline is 4000 ft tall
This Monocline is barely 5 feet
thick.