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Environmental Science
Nick Eyles

EESA06 READING #3 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 motionHow 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 o Shallow focus o Intermediate focus o Deep 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 o Andes Mountains o El Salvador • (PAGE 84) Liquefaction – water-saturated soil or sediment turns from a solid to a liquid as a result of earthquake shaking which causes sinking • Aftershock • Foreshock Tsunami Tidal waves Tsunami aka Seismi
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