# Chapter 3 Notes

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4 Apr 2011
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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
-can move up to 725 km/ hr
-water keeps rising for five to ten minutes, causing great flooding
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## Document Summary

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. Damage to buildings depends greatly on the type of geological material it was built on and the type of construction. 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. 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 www. notesolution. com. This means that an increase of about 32 times of energy is released.

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