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Seismic Events
Causes of Earthquakes
Distribution of Earthquakes
Measuring Earthquakes
The Effects of Earthquakes
WHAT IS AN EARTHQUAKE?
•Sudden release of energy
•Creates seismic waves (similar to waves through water)
•Waves spread out spherically
•Greatest damage occurs at the epicentre
P & S waves
• Two types of wave explained.
• Circle of power demonstration.
• P & S travel through the interior of the earth – out from
the epicentre.
P-waves
• P waves (primary waves) are compressional
waves.
• In solids, these waves generally travel almost
twice as fast as S waves.
• P waves can travel through any type of material.
• In air, these pressure waves take the form of
sound waves.
• They travel at are 330 m/s in air, 1450 m/s in
water and about 5000 m/s in granite. (m/s =
meters per second.)
PRIMARY WAVE ‘p-wave’
– Longitudinal
– Sudden jolt felt as the quake hits.
S waves
• S waves (secondary waves) are transverse which means
that the ground is displaced perpendicularly (sideways)
to the direction of movement.
• The ground moves alternately to one side and then the
other. (or up or down… depending on the direction of the
wave.)
• S waves can travel only through solids, as fluids (liquids
and gases)
• Their speed is about 60% of that of P waves in a given
material.
• S waves arrive second in a seismic station because of
their slower speed.
• They are sometimes called shear waves.
SECONDARY WAVE ‘s-wave’
– Transverse (shake at right angles to the
direction of the wave.)
– Sustained shaking felt as quake hits
L wave
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The particle motion of a Love wave forms a horizontal line
perpendicular to the direction of movement (i.e. are transverse waves).
Since Love waves travel on the Earth's surface, the strength (or
amplitude) of the waves decrease exponentially with the depth of an
earthquake.
Surface waves therefore decay more slowly with distance than do body
waves, which travel in three dimensions.
Large earthquakes may generate Love waves that travel around the
Earth several times before dissipating.
Since they decay so slowly, Love waves are the most destructive
outside the immediate area of the focus or epicentre of an earthquake.
They are what most people feel directly during an earthquake.
LOVE WAVE. L-wave
Lets get an overview.
Read the book pages 24 - 27
Worksheet– Sheet 5 & 6
Distribution of Earthquakes
• What is the distribution of Earthquakes?
•Read the section in the book then use following
statements to make a short paragraph explaining the
distribution of Earthquakes.
–
–
–
–
The Pacific Ring of Fire
70% of Earthquake and Volcanic activity is found around it’s edges
Volcanoes and Earthquakes are frequent.
Represents the destructive plate boundaries around the edges of
the plate.
THE RICHTER SCALE
•Invented by Charles Francis Richter in 1935
•Measure of an earthquake’s magnitude
•Scale between 0 and 10(theoretically)
•Logarithmic scale
How does a seismograph work?
Measurement – using a seismograph
http://www.wwnorton.com/college/geo/egeo/flash/8_3.swf
Magnitude: A measure of the size of an earthquake.
Frequency: Is the number of occurrences of a repeating event
per unit time.
• Worksheet 1.10
Effects of an Earthquake
• National Geographic 4 min clip – the
effects of earthquakes. Link
• The text book explains several effects
– Liquefaction
– Landslides/avalanches
– Effects on built environment
– Tsunamis
Liquefaction Explained
http://www.youtube.com/watch?v=PwvvYxSZ
7PI
What happened in San
Francisco?
Year 9 Worksheet 1.20. 1.21.
Aftershocks
A tremor (or one of a series of
tremors) occurring after the main
shock of an earthquake
: Video
Mass Movement
when masses of rock, earth, or debris move down a slope.
• Mass movement is movement of masses of bodies of
soil, bed rock, rock debris, soil, or mud.
• They may be very small or very large, and can move at
slow to very high speeds.
• Usually occur along steep-sided hills and mountains
because of the pull of gravity.
• An avalanche is a sudden flow of a large mass of snow
or ice down a slope, sometimes at speeds exceeding
160 km/hr.
• Mass movement and avalanches can be started when
earthquakes destabilise rock and start a slide.
• http://www.youtube.com/watch?v=JrV4uCVwmfk
Tsunami • What is a Tsunami?
• Tsunami -a large wave, or series of
waves, caused when an earthquake
causes massive undersea crust
movements and/or collapses which
displace the water above.
• Earthquakes deform the ocean floor,
pushing the overlying water up into a
tsunami wave.
Video of Boxing Day Tsunami
• Tsunami – Caught on Camera
Scale
showing the
size of the
tsunami
waves that
hit Indonesia.
Case study – Boxing Day
Tsunami.
• Make a 5 point PowerPoint to get the key
facts about the Tsunami across. Use case
study on page 29 to help.
– Why it occurred.
– Where it started.
– What it effected.
– Positive side effects.
Plenary
Earthquakes don’t kill people,
buildings do.
Starter
Earthquakes don’t kill people…
BUILDINGS DO!!!
BUILDINGS
• Side to side forces that cause collapse
HOW TO BUILD
SMALL BUILDINGS
• Shear walls
• Concentrate the damage
• Cross Bracing
• Reinforced stone wall
LARGER BUILDINGS
• Base isolation
SKY SCRAPERS
• Tuned Mass Damper
HAITI
CHILE