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Slide 2 :
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Foci – location inside earth where an earthquake starts
Epicenter – Point on earth’s surface directly above the focus |
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Slide 3 :
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Anatomy of Earthquakes |
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Slide 4 :
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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 |
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Slide 5 :
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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 |
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Slide 6 :
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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 |
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Slide 7 :
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Smaller amplitude than surface (L) waves, but faster, P arrives first P and S waves |
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Slide 8 :
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Two Types of Surface Waves Most of the destruction
Larger amplitude than body waves |
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Slide 9 :
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Why do P waves reach stations before S? Outer core is Liquid – S waves can’t travel through, but p can p 530 |
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Slide 10 :
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Surface waves L wave – Travels along the earth’s surface
Last to arrive
Ground motion is a rolling action like ripples on a pond |
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Slide 11 :
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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 |
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Slide 12 :
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A seismograph designed to record vertical ground motion The heavy mass doesn’t move much
The drum moves |
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Slide 13 :
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Lateral Movement Detector In reality, copper wire coils move around magnets, generating current which is recorded. |
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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 |
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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 |
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Slide 16 :
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Earthquake focus and epicenter |
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Slide 17 :
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Note how much bigger the surface waves are Body Waves Delay between P and S arrivals gives distance to epicenter |
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Slide 18 :
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Graph to find distance to epicenter |
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Slide 19 :
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Don’t need to know the next few slides, but it is cool to do ;) |
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Slide 20 :
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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 |
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Slide 21 :
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Locating Earthquake Epicenter |
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Slide 22 :
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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 |
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Slide 23 :
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Epicenter located using three seismographs |
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Slide 24 :
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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 |
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Slide 25 :
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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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