Transcript Earthquake Seismic Waves PowerPoint

What is an earthquake?
 An earthquake is a shaking of the earth
caused by a fracture (crack) in the earth.
This means the crust of the earth has
broken. The vibration may be as mild as a
sound like thunder in the distance to a
violent rocking of the ground beneath you
and falling buildings. When the
earthquake occurs, the breaking sends
seismic waves out from the location of
the quake.
What is a seismic wave?
 A seismic wave is a wave of energy that radiates
in all directions from the point of origin (focus) of
an earthquake. The epicenter is the point on
Earth’s surface directly above the focus.
What are the types of seismic
waves?
Some waves travel
through the body of
the Earth. There are
two types of these
waves:
 P-Waves
 S-Waves
Some waves travel
along the surface of
the Earth. These are
the waves that cause
the damage
associated with
Earthquakes. They
are known as:
 L-Waves
Properties of Body Waves
P-Wave Properties (Primary Waves) :
 Compressional Waves- motion of particles is parallel to
the direction of wave motion  Push-pull waves
 Passes through solids, liquids and gases.
 Arrive phirst because they have the greatest velocity
(phastest).
Properties of Body Waves
S-Wave Properties (Secondary Waves):
 Shear waves- particles move perpendicular to the
direction of motion.  Up-and-down waves
 Can travel through SOLIDS ONLY!
 Arrive at seismic stations second, after P-Waves, so
they are slower.
How do the velocities of
seismic waves differ?
 When traveling through the same material,
p-waves travel at a greater velocity than swaves. As a result, a seismograph will
record the p-wave arrival before the arrival
of the s-waves.
How are body waves used by
scientists?
 Scientists make
inferences about
Earth’s interior based
upon the behavior of
seismic waves as they
travel through the
Earth. The Outer Core
of Earth is presumed
to be liquid because SWaves “disappear” in
this region.
Shadow Zones
 Between 102° and 143°
of the epicenter of an
earthquake there is a
shadow zone where
neither P-Waves nor SWaves are received by
seismograph stations.
This is due to refraction
of P-Waves out of this
region, and the
absorption of S-Waves
in the outer core.
How are seismic waves
measured?
 Instruments called seismographs are used to
measure earthquake waves.
 A seismogram is the record of seismic activity
recorded by a seismograph.
Measuring Earthquake Intensity
 The Modified Mercalli Scale is based upon the
damage inflicted by an earthquake. This scale
ranges from I to XII.
 Can you think of a problem with using only this
scale to define earthquake intensity?
Measuring Earthquake Intensity
 The Richter Scale is a
magnitude scale used to
describe the amount of
energy released by an
earthquake.
 The scale generally ranges
from 0-9, but has no true
upper limit. Each step up
in the magnitude scale
indicates an increase in
energy released by 32X
over the previous step.
 Today in earthquake
history
Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPAN
Friday, March 11, 2011 at 05:46:23 UTC
Globally, Japan’s is the 4th largest earthquake since 1900.
Great (M > 8) Earthquakes Since 1900
9.6
Chile 1960
9.4
Alaska 1964
9.2
Magnitude
Sumatra 2004
Russia 1952
9
8.8
Japan 2011
Ecuador 1906
Chile 2010
Alaska 1965
8.6
8.4
8.2
8
7.8
1900
1920
1940
1960
Year
1980
2000
2020