EARTHQUAKES
FORCES IN EARTH’S CRUST
How does stress change Earth’s crust?
Stress is a force that acts on rock to change its shape
or volume.
Stress= force / unit of area
Pressure = Force / Area
The movement of Earth’s plates can
create strong forces that slowly bend
or fold many rocks like a caramel
candy bar.
An earthquake is the shaking of the ground cause by
seismic waves.
Tension, compression and shearing work over
millions of years to change the shape and volume of
a rock.
TENSION occurs where two plates pull
apart.
The stress force that pulls on the crust
and thins rock in the middle is called
tension.
COMPRESSION occurs where two
plates come together.
The stress force that squeezes rock
until it folds or breaks.
SHEARING occurs where two plates slip
past each other. Shearing can cause rock
to break and slip apart or to change its
shape.
HOW DO FAULTS FORM?
When enough stress builts up in rock,
the rock breaks, creating a fault.
Normal Fault.- Rock is pull apart by
tension.
The fault cuts through rock at an
angle, so one block sits over the
fault ( hanging wall) and the other
block lies under the fault ( footwall).
RIO GRANDE RIVER flows through a
wide valley in Mexico.
NORMAL FAULT
REVERSE FAULTS.- The blocks move in
the reverse direction. The hanging wall
moves up and the footwall moves
down.
R. F. form where compression pushes
the rock of the crust together.
The northern Rocky Mountains rise
high above the Western United States
and Canada.
STRIKE-SLIP FAULT. – The rocks slip
past each other sideways, with little
up or down motion.
They form when compression pushes
the rock of the crust together.
The hilly plains in Southern California.
San Andreas fault is an example of a
transform boundary.
Type of faults
SAN ANDREAS FAULT
SAN ANDREAS FAULT
1
1.
2.
2
3
Normal Fault.- hanging wall slips down relative to the
footwall.
Reverse Fault.-The hanging wall moves up relative to the
footwall.
3. Strike-slip fault Rocks on either side
4. Of the fault move past to each other.
Plate movements create new landforms
Over millions of years, the forces of plate
movement can change a flat plain into
features such as :
anticlines and synclines, folded
mountains, fault-block mountains, and
plateaus.
ANTICLINE
ANTICLINE
FOLDS are bends in rock that form when
compression shortens and thickens Earth’s
crust. A fold can be a few centimeters
across or hundreds of kilometers wide.
ANTICILINES AND SYNCLINES
( By Compression forces)
Upward and downward fold in rock.
A fold in rock that bends downward in to
form a V shape is a syncline.
The central Appalachian Mountains in
Pennsylvania.
EARTHQUAKES PLATE MOVEMENT
SYNCLINES
SYNCLINES
FOLDED MOUNTAINS
Collision of plates , compression and
folding of crust over a wide area.
Largest Mountain Ranges:
Himalayas ( Asia ), Alps ( Europe )
FOLDED MOUNTAINS
Folded mountains/ anticiclines
Salt Lake City to Los Angeles
Cross the Great Basin , region with many
mountains, valleys or basins.
Region formed by tension and faulting.
Fault-block mountains formed where two
plates move away from each other.
SALT LAKE CITY/ UTAH
GREAT BASIN . NEVADA
GREAT BASIN NATIONAL PARK NEVADA
GREAT BASIN /NEVADA
PLATEAUS
Large area of flat land elevated high
above sea level.
Forces that raise mountains , uplift a
large flat block of rock ( crust).
Plateaus have many different flat layers.
Colorado Plateau in the “Four Corners” ,
regions of Colorado, Utah , Colorado and
New Mexico.
COLORADO PLATEAU
LESSON 2
EARTHQUAKE is the shaking and
trembling that results from movement of
rock beneath Earth’s surface.
LOMA PRIETA .- SAN FRANCISCO
SEISMIC WAVES are vibrations, that are
similar to sound waves.
They travel through Earth carrying
energy released by an earthquake.
TYPES OF SEISMIC WAVES
•Focus point
•Epicenter
•P waves.- waves that compress and
expand
•S Waves .- waves that vibrate side to
side. Vibrations at an angle 90 to the
direction that they travel.
P Waves travel through liquids and
solids.
S waves can not move through liquids.
S waves reached the surface and shake
structures violently.
Surface waves are P or S waves that
reach the surface.
S.W. move more slowly than P or S
waves, but they can produce sere
ground movements.
KABUL INDU KUSH REGION ( AFGHANISTAN )
Most earthquakes start in the
lithosphere within about 100 Km.
beneath Earth’s surface.
Seismic Waves carry energy.
P WAVES
CAN VIBRATE THE GROUND
SIDE TO SIDE
S WAVES
CAN MAKE THE GROUND ROLL
LIKE THE OCEAN WAVE
SURFACE WAVES
CCOMPRESS AND EXPAND THE
GROUND
SEISMOGRAPH is an instrument that
records and measures an earthquake’s
seismic waves.
The magnitude or size of an earthquake
is measured on a seismograph using the
RICHTER scale.
The amount of earthquake damage or
shaking is rated using the Modified
Mercalli scale.
The Moment Magnitude Scale rates the
total energy an earthquake releases.