Download EARTHQUAKES

EARTHQUAKES
•  An earthquake is the shaking and trembling that results
from the movement of rock beneath the Earth’s
surface
•  There are about 1,000,000 earthquakes a
year; ONLY about 20 are considered severe
Seismology à study of earthquakes
Seismologist à scientist who studies
earthquakes and seismic
waves
Keep in mind: Seismologists don’t
have to be right near an
earthquake to study it. Why is this?
Fault à a break in the crust along which
plates shift and slip past each other
•  Where are faults found?
Plate boundaries & inside plates
What plate is surrounded
by earthquakes?
PACIFIC PLATE!
PLATE BOUNDARY FEATURES
Focus à Actual point of the shift along the fault
where the rock breaks
Usually miles underground
Epicenter à Closest point to the focus on the
earth’s surface
Always directly above the focus
Deformation à rocks changing shape due
to stress from tectonic
motion
Plastic
Deformation
Elastic
Deformation
Plastic
Deformation
Stress causing a
fold
Elastic
Deformation
Stress causing a
fold then a break
Elastic deformation causes earthquakes
because of the elastic rebound!
Elastic rebound à stress builds up to the point
where the rock breaks and
snaps back
ELASTIC REBOUND
Seismic waves à
• During an earthquake seismic waves race
out from the focus in all directions
•  Can you label them on your notes?
• Carry waves of energy from an earthquake
away from the
focus through Earth’s interior
and across the surface
Different types of seismic
waves travel through the
Earth’s layers at different
speeds.
Body Waves à Seismic waves that move
through Earth (P and S waves)
•  Primary or pressure waves
•  Travel through solid and
liquid (entire Earth)
•  fastest wave
•  particles move in a back &
forth direction the same
direction as the wave
(longitudinal)
In one direction
Radiating out from epicenter
•  Secondary or shear wave
•  Travel only through solid
(not liquid)
•  Move slower than Pwaves
•  Particles move in an up
and down motion
perpendicular to the
direction of the wave
(transverse)
In one direction
Radiating out from epicenter
Both can be
easily
demonstrated
with a Slinky!
Surface Waves à Seismic waves that travel on
the surface of Earth (L
L-waves
• Love wave (surface)
waves)
• Travel only on the surface
• Slowest but most
destructive
• Moves like an ocean wave
– up, down, and around
Surface wave
SEISMIC WAVE MOTION
SEISMIC WAVE MOTION WITH SURFACE EFFECTS
P-waves
(Pressure waves)
S-waves
(Shear waves)
Relative Speed:
Relative Speed:
fastest
slower
back and forth
Up and down
Where they travel:
Where they travel:
through the entire
earth
only through solid
Surface waves
Relative Speed:
slowest,
but most damaging
up, down, and
around
Where they travel:
on the earth’s
surface