Earth Shattering POWERPOINT
1
What is an earthquake?
• A sudden movement of the earth's crust
caused by the release of stress
accumulated along plate boundaries or by
volcanic activity.
2
How does an Earthquake occur?
•
•
•
Rock remains locked until the strain
becomes so great the rock suddenly
breaks and slips past each other.
When rocks break, it releases energy
(seismic waves)
Called Elastic Rebound theory
3
Elastic Rebound Theory
• As tectonic plates are slowly moving, their
edges are locked in place, causing bending
of the crust along plate boundaries.
The original position before any
change has occurred.
As plates slide past eachother,
the rock bends and folds
4
Elastic Rebound Theory
• When the force trying to make the edges slip
overcomes the friction making them stick,
there is an earthquake.
• The bending and “springing back” of the rock
is called elastic rebound.
• Elastic Rebound Animation- Click HERE
Rock breaks and releases
energy.
The rock rebounds (springs)
back to its undeformed shape.
5
Images of elastic rebound
6
7
8
Earth Sci
rocks
9
• Pretty sure
they didn’t
build the
fence like
this!
10
Seismic Waves
• Energy waves caused by the release of
pressure caused by the movement of
tectonic plates.
11
Seismic Waves
• There are 2 divisions of seismic waves
1. Those that travel through the Earth
(Body Waves)
2. And those that ONLY travel on the crust
(Surface Waves)
12
Body Waves
• Body waves can travel in the interior of the
Earth.
• There are TWO Body Waves:
– Primary Wave, or P-wave, travels the fastest
9km/second or 5.5mi/second
– Secondary Wave, or S-wave, travels a little
slower.
6km/sec or 3.5mi/sec
13
P-waves
• Can travel through the entire Earth. Through
liquids (outer core) and solids (inner core).
• The type of wave is called compression. It
compresses (squeezes) the matter it’s moving
through. (*** your chem teacher might call it longitudinal)
• Click HERE for P-waves animation
14
S-waves
• S-waves can travel only through the SOLID
portion of the interior of the Earth.
• They cannot travel through liquids, so they
cannot travel through the outer core.
• The wave is called a shear wave. Matter is
moved perpendicular to motion of energy.
(*** Your chem teacher would call this a transverse wave).
• Click HERE for animation of S-waves
15
Surface Waves (also called L-waves)
• Move much slower than the body wave- roughly
speed of sound. Only 1 mile in 5 seconds (or
about 700 mi/hr)
• Can only travel through the crust of the Earth
(surface).
• These waves have the biggest amplitude (height
of the wave). As a result they do the MOST
damage on the surface.
• Click HERE for animation- scroll down to the
bottom and look at Rayleigh surface wave.
16
How are Earthquakes USEFUL?
•
•
Seismic waves allow us to find the
epicenter (location) of an EQ.
Seismic waves help us determine the
interior of the Earth.
17
How do seismic waves help us find the Earthquake?
• Because the P wave and S wave travel at a
constant speed, we can determine the distance of
an earthquake from a seismic station.
18
How do Seismic waves help us determine
the interior of the Earth?
• P waves can travel
through the entire Earth.
• S waves can only travel
through the crust and
mantle.
• This causes seismic
wave “shadows”
• Click HERE for an
animation of seismic
waves traveling through
the Earth.
19
How do we measure the strength of
an Earthquake?
•
•
Richter Scale
used to rate the magnitude of an
earthquake the amount of energy it
released.
It is a logarithmic scale, meaning that
whole-number jumps indicate a tenfold
increase.
•
–
–
Richter scale???
Example: Magnitude 5 EQ is 10 times stronger
than a magnitude 4 EQ (10 times the ground
motion!!!)
Magnitude 6 EQ is 10 x 10 (or 100) times
stronger (100 times the ground motion)
20