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Chapter 3

Chapter 3 Notes


Department
Environmental Science
Course Code
EESA06H3
Professor
Nick Eyles
Chapter
3

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Chapter 3
EARTHQUAKES
What Causes Earthquakes?
-seismic waves: cause the earth to shake
-the earth puts stress on the rock, and it bends (strain)
-elastic rebound theory: the sudden release of stored elastic strain energy in rocks, causing
movement along a fault
-tectonic forces act on a mass of rock over many decades
-maximum depth of focus is 670km
-shallow focus: 0-70km
-intermediate focus: 70-350 km deep
-deep focus: 350- 670 km
Measuring the Size of an Earthquake
-damage to buildings depends greatly on the type of geological material it was built on and
the type of construction
-stone houses suffer more than wooden ones
-can also calculate the amount of energy released; done by measuring the squiggles on a
seismogram
-Richter scale is open ended which means there is no earthquake too big or too small
-8.6 is the biggest recorded so far
-can also measure the seismic movement; determined from the strength of the rock, surface
area of the rupture, and amount of rock displacement along the fault
-Richter scale is logarithmic, so the difference between 2 consecutive numbers on the scale
means an increase of 10 times the amplitude
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-this means that an increase of about 32 times of energy is released
Location and Size of Earthquakes in NA
-BC is most active, about 200 quakes per year; biggest was 8.1
-usually on old divergent plate boundaries and failed rifts
-earthquakes in the St. Lawrence area occur because the St. Lawrence is a failed rift system
What Kinds of Damage Can Earthquakes Cause?
-ground motion can destroy buildings
-fire can happen from broken gas mains and fallen electrical wires
-landslides
-liquefaction: when water saturated soil or sediment turn liquid due to shaking
-permanent displacement of land surface; rocks can move vertically or horizontally, can
form a scarp; closed tear in the ground
-aftershocks are small earthquakes that follow the main event; can tear down already
weakened buildings
-buildings that are strongest in earthquakes are steel, wood, and reinforced concrete;
strong, flexible, and light materials
Tsunami
-sudden movement of the sea floor up or down displaces the entire water column and
creates huge tidal waves
-or can be from submarine or volcanic explosions
-pg 87 for more info
-can move up to 725 km/ hr
-water keeps rising for five to ten minutes, causing great flooding
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