# EESA06H3 Chapter Notes -Cascadia Subduction Zone

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26 Apr 2012
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EESA06
CHAPTER 3 – EARTHQUAKES
What causes earthquakes? Page 68-72
Earthquake
Stress
Strain
Seismic waves
Fault
Elastic rebound theory (DIAGRAM PG.68)
Tectonic forces
Indonesia Sumatra Earthquake and Tsunami 2004 (PAGE 69)
Magnitude 9.3
Release of energy between the India Plate and Burma Plate
Thrust fault
‘Megathrust’ – created tsunami
Inundation – the distance from the shoreline to the limit of
tsunami penetration
Run-up Elevation – the elevation above sea level of the water
surface at the inland limit of inundation
Tsunami lost energy as it moved inwards
Why do earthquakes cause so much damage? (Page 72-73)
Focus (hypocentre)
Epicentre
Two types of Seismic Waves:
a. Body Waves
a. P Waves – Compressional/Parallel
i. Solid
ii. Liquid/Gas
b. S Waves – Perpendicular
i. Solid
b. Surface Waves (Slow/damaging)
a. Love Waves
i. Like S waves
ii. Move side to side horizontally
iii. Not thorough liquids
b. Rayleigh Waves
i. Rolling ocean waves
ii. Circular motion
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How do we know where earthquakes occur? (Page 73-79)
Seismometer – measure seismic waves
Seismograph –recording device of Earth’s motion
Seismogram – paper record
Order during earthquake:
1. P waves
2. S Waves
3. Surface Waves
Determining the Location of an Earthquake (Page 75)
Time interval between the first arrivals of P and S waves increases
with distance from the focus of an earthquake, this interval can be
used to determine the distance from the seismograph station to a
earthquake
Travel-Time curve
Focus/Epicentre/etc. (DIAGRAMS PAGE 75)
Depth of focus – distance between focus and epicentre
oShallow focus
oIntermediate focus
oDeep focus
Measuring the Size of an Earthquake
1. Intensity – modified Mercalli Scale (DIAGRAM PG.77)
2. Magnitude – Richter Scale (DIAGRAM PG.78)
3. Moment Magnitude (DIAGRAM PG.79)
i. Quake of 5 releases 32 times more energy than one of
magnitude 4. Quake of 6 is (32 X 32) more powerful than a
quake of 4.
Location and Size of Earthquakes in North America (PG.79)
BC
California
Quebec
What kinds of damage can earthquakes cause? (Page 79-88)
Ground motion
Falling buildings
Fires
Landslides
oAndes Mountains
(PAGE 84) Liquefaction – water-saturated soil or sediment turns
from a solid to a liquid as a result of earthquake shaking which
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