TOPIC:
KS3
Seismic Waves Transferring Energy
13
Which of the following statements about earthquakes are true?*
The global location of earthquakes closely resembles the distribution of volcanoes.
There are thousands of earthquakes across the planet every day.
Earthquakes are created by the sudden release of energy in the earth’s crust.
The shallower an earthquake the more damage it creates to structures.
When the epicentre of an earthquake is in the ocean, it can create a tsunami.
The earth’s outer shell or mantle and crust allow plates to move.
Earthquakes are most common at the points where one plate moves under another.
Earthquakes are measured on the Richter Scale from 1-10.
A level 7 earthquake is 100 times more powerful than a level 5 quake.
*Answer: They’re all true!
EARTHQUAKES CAN BE PREDICTED
What to do:
You are going to make a seismograph. First you
need to understand how a seismograph works.
A typical seismograph works in a very simple way:
• A heavy weight is fastened to a horizontal rod.
• This rod hangs from a pole and is free to swing
from side to side when the ground shakes.
• At the other end of the rod (away from the
pole) is an ink pen, and directly underneath the
pen is a piece of paper rolled around a cylinder.
• This cylinder rotates so that the pen
continuously draws an ink line along the
moving paper.
Science Technology Engineering Maths
If the ground does not move,
the rod does not swing, and
the pen stays in place, so the
ink line is smooth and straight.
If the ground shakes,
however, the rod
swings and so
the pen draws
a zigzag line as the
paper turns. The stronger the shaking, the sharper the
zigzags. This zigzag picture made on the paper roll is
called a seismogram.
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ENERGY AND WAVES
Seismology is the study of earthquakes and seismic
waves that move through and around the earth. Seismic
waves are the waves of energy caused by the sudden
breaking of rock within the earth or an explosion.
TOPIC:
Seismic Waves Transferring Energy
Think of a creative but effective way to
measure the seismic waves (shock waves)
from an earthquake. Draw a clear diagram
that shows and labels all parts. Then
write a paragraph explaining how your
design works. A good design might be...
Check out the face fuzz on the two
impornt British seismologis!!
• made of ordinary inexpensive
materials which you can source easily
• able to determine the relative
magnitude (size) of each vibration it
measures
• able to measure vibrations
continuously for at least one minute
• able to measure even slight vibrations
(such as your friend jumping up and down
next to your seismograph!)
There are several
different kinds of seismic waves,
and they all move in different ways.
The two main types of waves are body waves
and surface waves. Body waves can travel
through the earth's inner layers, but surface
waves can only move along the surface of the
planet like ripples on water. Earthquakes radiate
seismic energy as both body and surface waves.
Travelling through the interior of the earth,
body waves arrive before the surface waves
emitted by an earthquake. These waves
are of a higher frequency than
surface waves.
Love Waves
The first kind of surface wave is called a Love wave, named after
A.E.H. Love, a British mathematician who worked out the
mathematical model for this kind of wave in 1911. It's the fastest
surface wave and moves the ground from side-to-side. Confined to
the surface of the crust, Love waves produce entirely horizontal
motion.
Rayleigh Waves
The other kind of surface wave is the Rayleigh wave, named after
John William Strutt, Lord Rayleigh, who mathematically predicted
the existence of this kind of wave in 1885. A Rayleigh wave rolls
along the ground just like a wave rolls across a lake or an ocean.
Because it rolls, it moves the ground up and down, and side-to-side
in the same direction that the wave is moving. Most of the shaking
felt from an earthquake is due to the Rayleigh wave, which can be
much larger than the other waves.
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13
ENERGY AND WAVES
What to do:
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KS3
P
13
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The first kind of body wave is the P wave or primary wave. This is the fastest
kind of seismic wave, and, consequently, the first to 'arrive' at a seismic
station. The P wave can move through solid rock and fluids, like water or the
liquid layers of the earth. It pushes and pulls the rock it moves through just
like sound waves push and pull the air. When you hear a sound outside that is
‘loud’ enough to make the windows rattle it’s because the sound waves were
pushing and pulling on the window glass. In the same way P waves push and
pull on rock. Although people can only feel the bump and rattle of these
waves, some animals can hear them; dogs, for instance, commonly begin
barking hysterically just before an earthquake 'hits'. Can you explain why?
Subjected to a P wave, particles move in the same direction
that the wave is moving in, which is the direction that the
S Waves
energy is travelling in.
The second type of body wave is the
S wave or secondary wave, which is the
second wave you feel in an earthquake.
An S wave is slower than a P wave and
can only move through solid rock, not
through any liquid medium. It is this
unique property of S waves that led
seismologists to conclude that the
Earth's outer core is a liquid. S waves
move rock particles up and down, or
side-to-side--perpendicular to the
direction that the wave is travelling in.
Did
I
S
Travelling only through the crust, surface waves are of a lower
frequency than body waves, and are easily
distinguished
on a
In what
ways do
seismogram as a result. Though theyyou
arrive
after
body
waves,
it
think that
is surface waves that are almost entirely responsible for the
Fibre
damage and destruction associated
withOptic
earthquakes. This
Cableswaves
contribute
damage and the strength of the surface
are reduced
in deeper earthquakes.
to the systems on
What to do:
board the Astute?
Research the following examples of seismic activity. How
does your understanding of P and S waves help you to
make sense of these earthquakes, tsunamis and volcanic
eruptions and the resultant tragedies that unfolded?
Indian Ocean Earthquake and Tsunami Boxing Day 2004
Taiwan February 2016 ∞ Kashmir, Pakistan October 2005
Ruiz, Colombia 1985 ∞ United Kingdom February 2008
Popocatepetl, Mexico – up to and including 2016
Mount Etna – dates up to and including 2015
Check out the British Geographical Survey to find out about earthquakes in UK!
Science Technology Engineering Maths
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ENERGY AND WAVES
P Waves
KS3
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TOPIC:
Seismic Waves Transferring Energy