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 1 : Earthquake
 2 : Foci – location inside earth where an earthquake starts Epicenter – Point on earth’s surface directly above the focus
 3 : Anatomy of Earthquakes
 4 : Amount of Damage is dependant on depth Foci is close to surface – lots of damage Foci is far from surface – little damage – energy has to travel a long way
 5 : Seismic waves – p 529 3 Types: P, S, and L L waves – surface waves – roll along the earth’s surface Body waves: P and S waves Body waves travel faster than surface waves- feel p and s waves first after an earthquake
 6 : Body waves P wave- Primary wave -first to arrive Ground squeezes and streches in the direction of wave travel Travels through solids and liquids S wave- secondary wave -second to arrive Ground is perpendicular (90) to direction of wave travel Travels through solids but not liquids Another name for S-wave is shear wave
 7 : Smaller amplitude than surface (L) waves, but faster, P arrives first P and S waves
 8 : Two Types of Surface Waves Most of the destruction Larger amplitude than body waves
 9 : Why do P waves reach stations before S? Outer core is Liquid – S waves can’t travel through, but p can p 530
 10 : Surface waves L wave – Travels along the earth’s surface Last to arrive Ground motion is a rolling action like ripples on a pond
 11 : Seismology Seismometers - instruments that record seismic waves Records the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape
 12 : A seismograph designed to record vertical ground motion The heavy mass doesn’t move much The drum moves
 13 : Lateral Movement Detector In reality, copper wire coils move around magnets, generating current which is recorded.
 14 : Seismograms tell : How long an earthquake lasted and the amount of ground shaking Magnitude – rates the strength of an earthquake Higher the magnitude the stronger the earthquake
 15 : Each 1 step increase in magnitude = 10 times the size of seismic waves Seismograms determine how fast seismic waves are travelling. Look at p531 P waves = 5.5 min and S = 10 min
 16 : Earthquake focus and epicenter
 17 : Note how much bigger the surface waves are Body Waves Delay between P and S arrivals gives distance to epicenter
 18 : Graph to find distance to epicenter
 19 : Don’t need to know the next few slides, but it is cool to do ;)
 20 : Locating the epicenter of an earthquake Three seismographs needed to locate an epicenter Each station determines the time interval between the arrival of the first P wave and the first S wave at their location A travel-time graph then determines each station’s distance to the epicenter
 21 : Locating Earthquake Epicenter
 22 : Locating the epicenter of an earthquake A circle with radius equal to distance to the epicenter is drawn around each station The point where all three circles intersect is the earthquake epicenter
 23 : Epicenter located using three seismographs
 24 : Earthquake Belts 95% of energy released by earthquakes originates in narrow zones that wind around the Earth These zones mark of edges of tectonic plates
 25 : Locations of earthquakes from 1980 to 1990 Broad bands are subduction zone earthquakes, narrow are MOR 80% of seismic energy around Pacific Rim

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