Transcript An earthquake is a shaking of the ground caused by the sudden

Wednesday January 2, 2013
What is an earthquake? (yes, I will
be checking your answers!)
What is an Earthquake?
An earthquake is a shaking of the
ground caused by the sudden breaking
and shifting of large sections of Earth's
rocky outer shell.
The movement of the Earth’s plates creates
powerful forces that squeeze or pull the rock
in the crust. These forces are examples of
stress.
The three types of boundaries
Types of stress
Tension
The crust is pulled, stretching
the rock thinner in the middle.
Compression
The rock is squeezed
until it folds or breaks.
Shearing
Rock is pushed in opposite directions causing a break or slip
When enough
stress builds up in
rock, the rock
breaks, creating a
fault. A fault is a
break in the crust.
There are 3 types of faults
1 Strike-slip faults: this is where the
rocks slide past each other. This
occurs along transform boundaries.
(EX. The San Andreas fault)
There are 3 types of faults
1 Normal Faults:
this is where tension
forces cause one
side to rise above
the other. This
happens along
divergent
boundaries (EX. The
Rio Grande rift
valley).
There are 3 types of faults
3. Reverse Faults: this is where compression
forces cause one side to rise above the other.
Often times mountains are formed along these
faults.
(EX. The Appalachian mountains)
Friction
• Where friction is low,
the rocks slide past
each other easily.
• Where friction is
moderate, the sides
jam and jerk producing
small earthquakes.
• Where friction is
high, the rocks lock
together. Stress
builds until a major
earthquake occurs.
Where do earthquakes occur?
Most earthquakes occur along
plate boundaries or stress
points.
The latest seismic activity
Measuring Earthquakes
• Seismic waves are
vibrations that travel
through Earth carrying
energy released during
an earthquake.
• They travel from the
focus, through the
Earth’s interior, and
across the surface.
• The epicenter is the
point on the Earth’s
surface directly above
the focus.
Seismic Waves
• P waves or primary waves
cause the ground to compress
and expand like an accordion.
• P waves are the fastest
seismic waves. And they can
travel all the way through the
earth.
• P waves create a push/pull
effect.
Seismic Waves
• S waves or secondary
waves cause the
ground to shake up
and down.
• These waves can
only travel through
solid material, thus
when the waves hit
the outer core they
stop.
Seismic Waves
– Surface waves are the third
type of wave.
– These are the waves that
produce the most destruction.
– Surface waves are limited to
travel along only the surface of
the Earth.
Measuring Earthquakes
• A seismograph
records the ground
movement caused by
seismic waves.
• The magnitude is the
measurement of the
earthquake strength
based on the seismic
waves and movement
along faults.
SCALES
Charles Richter
• The Mercalli scale was
developed to rate
earthquakes according to
their intensity. It is not as
accurate as the . . .
• The Richter scale is a
rating of the size of
seismic waves measured
by a seismograph.
• The Moment Magnitude
Scale is a rating system
that estimates the total
energy released by an
earthquake. It is the most
accurate.
Mountain building
• Mountains formed by
faulting are called
fault-block mountains
• These mountains are
formed when two
normal faults mirror
each other.
• Mountains and
valleys are formed in
this way.
• The Great Basin
Mountain building
• Folds are bends in
rock that form when
compression forces
are present.
• Collision of plate
boundaries can cause
folded mountains.
• These collisions can
lead to earthquakes
due to faults
produced.
• The Himalayas and
the Alps
Anticlines and Synclines
• These terms
describe the folds in
the rock.
• A fold that bends
upward into an arch
is an anticline.
• A fold that bends
downward to form a
bowl is a
syncline.