Download S waves

Characteristics
of Earthquake
EARTHQUAKE CAUSES:
Stress builds along faults until the
elastic limit is exceeded.
FAULT: Surface along which rocks move
when they pass their elastic limit and
break.
Energy is released as seismic waves.
Ring of Fire
The "Ring of Fire",
also called the CircumPacific belt, is the
zone of earthquakes
surrounding the Pacific
Ocean--about 90% of
the world's
earthquakes occur
there. The next most
seismic region (5-6% of
earthquakes) is the
Alpide belt (extends
from Mediterranean
region, eastward
through Turkey, Iran,
and northern India.
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Faults Provide Energy
• Focus: location
beneath Earth’s
surface where an
earthquake begins.
• Epicenter: location
on Earth’s surface
directly above the
focus.
SEISMIC WAVES: waves generated
by an Earthquake.
EARTHQUAKE: Vibrations produced when
rocks break along a fault.
HOW DO WE MEASURE
EARTHQUAKES?
Seismic waves are recorded
on a machine called a
SEISMOGRAPH
SEISMOGRAM: is the vibration
record. (paper)
..\509.51 seismograph.avi
..\..\MS PowerPoint\seismograph.asx
EARTHQUAKES PRODUCE 3 TYPES OF
SEISMIC WAVES
1.Primary Waves – (P waves)
• P waves move out from the
earthquake focus.
FOCUS: the point where the energy
is released.
• They travel the fastest
• Move through liquid and solid
layers of Earth.
• They are LONGITUDINAL waves
(back and forth motion)
2. Secondary Waves – (S waves)
• They travel slower than P
waves.
•They are TRANSVERSE waves
• Move out from the earthquake
focus.
• They can only move through
SOLID rock.
• Move at right angles to
primary waves causing rocks to
move up and down and side to
side.
The 3rd type of wave are the
3. Surface Waves
• Form when P and S waves
reach the surface. (epicenter)
• Cause the ground to shake
making rock sway from side to
side and roll like an ocean wave.
•Cause the most damage!
Body Wave
P Waves in Motion
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Body Wave
S wave in motion
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Surface Wave
L wave in motion
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P waves are the fastest wave
S waves are slightly slower
L waves are the slowest of the
three waves
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Create a Venn Diagram on Seismic waves
S-Waves
P-Waves
• Move the fastest
• Longitudinal
waves
• Move
through
solids and
liquids.
• Move slower than
• Move
P-waves
out from
• Transverse
the Focus
waves
Caused by E.Q.
• Movement
is both P and
S waves.
Surface-Waves
• Move the slowest
• Found at the surface (epicenter)
• Most destructive
• Move
through
solids
only.
IN ORDER TO FIND THE
EPICENTER, YOU MUST HAVE
RECORDING STATIONS (3
seismographs)!
TRIANGULATION METHOD
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Locating an Earthquake
This method is
referred to as
TRIANGULATION
•You need the S – P time from
three different stations
•Once the S – P time is
determined you draw a circle
around the stations location
•It is only with a third station's
S-P time that you can determine
the exact location of the
earthquake
You will need to measure the time between
the arrival of the P and S waves to determine
the distance between the recording
seismograph and the earthquake epicenter.
Richter Scale – Determining the MAGNITUTE OF
AN EARTHQUAKE
The scales in the
diagram above
form a
nomogram
that allows you to
do the
mathematical
computation
quickly by eye.
The equation for
Richter Magnitude
is:
As time passes, the P and S waves will get
farther apart from each other. (student demo)
By knowing the difference between the P and
S wave, you are then able to determine
how far away the Earthquake was from the
Seismograph.
Measurement Scales
• Richter Scale: based on the times and
amplitudes of seismic waves by certain
seismographs.
• Moment Magnitude Scale: measures amount
of energy released. Each unit (MW)
represents about a 32-times increase in the
energy released.
• Modified Mercalli Scale: ranges 1-12 based
on observations of the intensity of ground
shaking and damage in the areas affected by
an earthquake.
Scientists use the principle that the speed
and direction of a seismic wave depends on
the material it travels through.
Because of the behavior of these different
waves, scientists have indirect evidence for
the solid inner core and liquid outer core of
Earth;
Because earthquake waves travel faster
through the mantle than through the
crust, scientist know that the mantle is
denser.
•Movement in the outer core of
Earth is inferred to be the cause
of Earth’s magnetic field.
• Compass needle will align with
the lines of force of Earth’s
magnetic field.
• Iron and nickel are metals that
easily magnetize and are inferred
to be the metals in Earth’s core.
Moho
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The Moho is the boundary
between the crust and the
mantle in the earth. This is a
depth where seismic waves
change velocity and there is
also a change in chemical
composition. Also termed the
Mohorovicic' discontinuity
after the Croatian seismologist
Andrija Mohorovicic' (18571936) who discovered it. The
boundary is between 25 and 60
km deep beneath the
continents and between 5 and
8 km deep beneath the ocean
floor.
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What is RESONANCE?
Every object tends to vibrate at one
particular frequency called the natural
frequency.
The measure of natural frequency depends on the
composition of the object, its size, structure,
weight and shape.
If we apply a vibrating force on the object with its
frequency equal to the natural frequency, it is a
resonance condition.
New Zealand Earthquake
Sept. 3 2010
Haiti Earthquake – January 2010
Haiti Earthquake – January 2010