Transcript Seismic Waves

Falcon Focus
Essential Question
Standard 8-3.8
EARTHQUAKES
Assessing Prior Knowledge
and Relativity
• What have you heard about
earthquakes lately?
• Why should we study earthquakes?
INTRODUCTION
• http://video.nationalgeographic.com/video/p
layer/environment/environment-naturaldisasters/earthquakes/earthquake-101.html
The definition of an earthquake is…
vibrations that cause the breaking of
rocks.
These vibrations move in all directions
through the earth. They begin at a point
along a fault.
Earthquakes
• If the __pressure___ or stress becomes too
great, the rock breaks at a weak point along
the fault and ___energy_____ is released
Epicenter
Focus
aaALONG THE FAULT
Parts of the Earthquake
• The energy spreads outward in all directions as
vibrations called ____seismic waves_____.
• The _focus____ of the earthquake is the point in
the crust, or mantle, where energy is released.
• The _epicenter___ is the point on Earth’s surface
directly above the focus; energy that reaches the
surface is greatest at this point.
Focus –
point inside the Earth where an
earthquake begins
Epicenter – point on Earth’s surface above focus
Focus, Epicenter, and Fault
RECAP
• (Take a minute to fill
in the blank)
ANSWERS
• Epicenter: is located right above the
focus and has the greatest amount of
energy
• Focus: releases the energy (seismic
waves)
• Fault: a break in the Earth’s Crust (is
where an earthquake takes place)
• Seismic waves: is the energy that is being
sent out from the focus
Use the words above to Label
the Following parts of the earthquake.
ANSWERS
• A:
• B:
• C:
• D:
FOCUS
EPICENTER
FAULT
SEISMIC WAVES
What Causes an Earthquake?
Cause of Earthquakes
 Aftershocks and Foreshocks
• An aftershock is a small earthquake that
follows the main earthquake.
• A foreshock is a small earthquake that often
precedes a major earthquake.
…And that was
just a 7.2 on
the Richter
scale!
QuickTime™ and a
GIF decompressor
are needed to see this picture.
SEISMIC WAVES
• 8-3.2
Explain how scientists use
seismic waves – primary, secondary, and
surface waves – and Earth’s magnetic
fields to determine the internal structure
of Earth.
3 TYPES OF SEISMIC WAVES
• PRIMARY (P) WAVES
• SECONDARY (S) WAVES
• SURFACE WAVES
CONSIDERED AS BODY WAVES
SEISMIC WAVES
• _SEISMIC WAVES___ are waves
generated by an earthquake that travel
through the Earth. These waves can cause
the ground to move forward, backward,
up, down, and even to ripple. Seismic
Waves are generated at the __SAME___
time but move in different ways, and at
different speeds.
Seismic
Waves in
the Earth
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
SEISMIC WAVES
• Scientists use the principle
that the speed and direction
of a seismic wave depends
on the material it travels
through.
How does scientist know or
study the Earth’s Core?
• Because of the behavior of these different
waves, scientists have indirect evidence
for the solid inner core and liquid outer
core of Earth because S waves don’t
travel through the outer core because it’s
a liquid. Also because earthquake waves
travel faster through the mantle than
through the crust, scientists know that the
mantle is denser than the crust.
Seismic Waves
PRIMARY (P) WAVE
• First Wave to Move out from the
earthquake focus, the point where the
energy is released
• Travel the fastest of the three waves
• Push and pull rock creating a back-andforth motion in the direction the wave is
moving
• (known as longitudinal or compressional
waves)
P WAVES
• Move through solid and
liquid layers of Earth
(therefore it can move
through all layers)
Primary Waves (P Waves)
• A type of seismic wave that compresses
and expands the ground
• The first wave to arrive at an
earthquake
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Secondary Waves (S Waves)
• 2nd wave to Move out from the
earthquake focus
• Move slower than primary waves
• Move at right angles to primary waves
causing rocks to move up and down
and side to side (known as transverse
wave: perpendicular to the wave
motion)
S WAVES
• Can only move through SOLID
rock therefore it CAN NOT
TRAVEL THROUGH THE
OUTER CORE because it is a
LIQUID. IT STOPS AT THE
OUTER CORE.
Secondary Waves (S Waves)
• A type of seismic wave that moves the
ground up and down or side to side
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Comparing Seismic Waves
SURFACE WAVES
• Form when P and S waves reach the surfacee
• SLOWEST BUT MOST DESTRUCTIVE
• Can cause the ground to shake making rock sway
from side to side and roll like an ocean wave
SURFACE WAVES
• Move through solid and liquid
layers of Earth (therefore it can
move through all layers)
Seismic Waves Paths Through the Earth
Earth’s Interior Showing
P and S Wave Paths
Earthquake Waves & Earth’s Interior
• 8-3.3 Infer an earthquake’s
epicenter from seismographic
data.
Measuring Earthquakes
• The energy spreads outward in all
directions as vibrations called
___Seismic Waves____. Seismic
waves can be measured and recorded
by a ____seismograph_______.
SEISMOGRAPH
Measuring Earthquakes
• The vibration record, called a
seismogram, looks like jagged lines on
paper. Measuring the time between the
arrival of the P and S waves
determines the distance between the
recording seismograph and the
earthquake epicenter.
SEISMOGRAM
Seismograph
Types of Seismographs
Seismogram Printout
• How to find the S-P
INTERVALS
• To find the S-P intervals, you have to
subtract the P Wave from the S
Wave.
• Measuring the time between the arrival
of the P and S waves determines the
distance between the recording
seismograph and the earthquake
epicenter.
• Find the S-P interval:
Show your steps.
PRACTICE
WHAT IS THE S-P
INTERVAL?
WHAT IS THE S-P
INTERVAL?
Locating an Earthquake
Locating an Earthquake Epicenter
• Triangulate means to use three positions to
determine an exact location.
• TRIANGULATION identifies the
epicenter of an earthquake. The
location of an earthquake’s epicenter
is found by plotting 3 circles on a map
from the records of three seismograph
stations and finding the point where
the three circles intersect. Note
where the 3 circles meet is where the
epicenter is located.
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Triangulation
of 3 stations
to locate
earthquake
epicenter
Earthquakes are measured using the Richter
Scale. The strongest earthquake ever
measured was a 9.5 on the Richter Scale. This
is a measurement of the amount of energy
released from the earthquake.
How are Earthquakes Measured? Richter
Scale
HOMEWORK