Download Where do earthquakes occur?

Earthquakes
(1)
What causes earthquakes?
It’s plate movement

Movement in the crust
causes stress– energy
that slowly changes the
shape of rock

Earthquake– shaking
from the sudden
movement of rock at a
fault (stress is quickly
released)
Bedarliex, France
Fault energy can be released all at
once and cause elastic rebound
(2) Where
do earthquakes occur?
Pacific Plate
N.A. Plate
(2)
Where do earthquakes occur?
1) At strike-slip faults, plates
move at sliding boundaries Pacific Plate
(San Andreas Fault, CA) 
N.A. Plate
(2)
Where do earthquakes occur?
1) At strike-slip faults, plates
move at sliding boundaries N. A. Plate
(San Andreas Fault, CA)
2) Large earthquakes can
occur at subduction zones,
colliding boundaries
(near Japan)

Pacific Plate
Where do earthquakes occur?
1) At strike-slip faults, plates
move at sliding boundaries
N. A. Plate
(San Andreas Fault, CA)
2) Large earthquakes can
occur at subduction zones,
colliding boundaries
(near Japan or Chile)
3) Smaller ‘quakes happen
at mid-ocean ridges & rift
zones, spreading boundaries
(Mid-Atlantic Ridge)

Eurasian
Plate
Epicenter & Focus
epicenter- point on
Earth’s surface
directly above the
focus
focus- area beneath
the surface, where
the release of fault
energy starts an
earthquake
(4)
What are seismic waves?
seismic waves- vibrations
made from the release of
an earthquake’s energy
These waves travel outward
from the focus…
(4)
What are seismic waves?
seismic waves- vibrations
made from the release of
an earthquake’s energy
These waves travel outward
from the focus…
…underground through
Earth’s body of solid rock
(P waves or S waves)
(4)
What are seismic waves?
seismic waves- vibrations
made from the release of
an earthquake’s energy
These waves travel outward
from the focus…
…underground through
Earth’s body of solid rock
(P waves or S waves)
…and above ground as
destructive surface waves
(L waves, long-waves)
(5)
How do waves move underground?
First, there are…
 P waves- Primary or
pressure waves are the
fastest, and cause rock
to compress & expand
(push-pull)
(6) Next, are underground…
 S waves- secondary
or
shear waves; travel
slower than primary
waves, up-and-down
(back and forth)
(7)
S waves can move through solids (rock),
but NOT through liquids or gases
What happens to
the S waves (blue)?
(8)
How do surface waves move?
P and S waves above the
ground…
…are L waves, called
surface wavesthe slowest waves;
slower than P & S waves
(8)
How do surface waves move?
P and S waves above the
ground…
…are L waves, called
surface wavesthe slowest waves;
slower than P & S waves
…cause severe shearing of
the ground (side-to-side)
…can make the ground roll
like waves on water
http://blogs.agu.org/mountainbeltway/cate
gory/japan/
 Penn. State Univ.
http://eqseis.geosc.psu.edu/~cammon/HT
ML/Classes/IntroQuakes/Notes/waves_an
d_interior.html
 Wikipedia

Where do earthquakes occur?
1) At strike-slip faults, plate
move at sliding boundaries Nazca Plate
(San Andreas Fault, CA)
2) Large earthquakes can
occur at subduction zones,
colliding boundaries
(near Japan or Chile)
3) Smaller ‘quakes happen
at mid-ocean ridges,
spreading boundaries
(Mid-Atlantic Ridge)
S. A. Plate
How does a magnitude 6
compare to a 5 ?
The waves are 10 times greater from a magnitude 6
than those from a magnitude 5 earthquake
A magnitude 6 releases about 30 times more energy
than a magnitude 5
Richter
Magnitude
Energy
Released
5
Strength
(amplitude)
X
6
10X
30Y
7
100X
1000Y
Y