Seismic Waves - ESC 11 · ¡Explain that seismic waves propagate outwards as wave fronts from the...
Transcript of Seismic Waves - ESC 11 · ¡Explain that seismic waves propagate outwards as wave fronts from the...
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Seismic Waves
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Earthquake Waves
óWhen fault slips, released energy travels outward in seismic waves ¡Outward from point on fault that first
slipped: focus (or hypocenter) ¡Epicenter is point on surface of Earth
directly above focus
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Types of Earthquake Waves óFirst arrival is P wave ¡Primary ¡Compressional motion ¡Feels like sudden jolt ¡Travels at 5-8 km/s through rock ¡Sometimes heard as low rumbling
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Types of Earthquake Waves óSecond arrival is S wave ¡Secondary ¡Shear motion ¡Feels like wiggling, difficult to stand ¡Travels at 3.5-4.5 km/s through rock ¡More destructive than P waves ¡Do not travel through liquids ¡Both P and S waves are body waves
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Types of Earthquake Waves
ó Last arrivals are surface waves ¡Include Love and Rayleigh waves ¡Travel along surface of Earth and fade
downward ¡Long, rolling motion ¡Travel slower than P or S waves ¡Can be more destructive than P or S waves
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Seismic Wave Videos
óP-wave óS-wave óRaleigh wave óLove wave
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Types of Earthquake Waves óWave terminology ¡Period: time for one complete cycle between
successive wave peaks to pass ¡Wavelength: distance between wave crests ¡Amplitude: amount of positive, negative wave
motion ¡Frequency: number of peaks per second
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Fig. 3-19, p. 45
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Seismographs
§ Seismographs record shaking of earthquake waves on seismograms § How do we stand still and watch the Earth move? § Heavy weight suspended from rigid column anchored to ground:
stays still from its own inertia while ground moves
§ Pen attached to weight marks paper attached to ground
§ North-south, east-west and vertical components
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Fig. 3-20, p. 45
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Figure 3-21a p45
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Figure 3-21b p45
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Figure 3-21c p45
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Earthquake-Wave Velocities ó Surface waves travel with constant velocity through
shallow rocks: arrival times increase linearly with distance ó P waves and S waves travel faster as they go deeper through the Earth: waves at greater depths reach seismograph along curving paths
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LIKE RIPPLES ON WATER
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Content Objectives
óStudents will be able to: ¡Explain that seismic waves propagate outwards
as wave fronts from the source in 3-dimensions (X, Y, & Z axes) and have a velocity
¡Explain that the amplitude of seismic waves is related to the amount of energy released from the source and decreases with distance from the source
¡Compare and contrast seismic waves to ripples on water.
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Videos
óLike ripples óUnlike ripples óUSA array tutorial óNevada earthquake animation USA
array óMid-Indian-Ocean earthquake
animation USA array
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Human Wave Demonstration
óObjective Students will: ¡Model how earthquake waves travel at
different speeds ¡Construct a distance and time graph to
represent the P and S waves ¡Visualize why s-waves do not travel
through liquids
óVIDEO: The Human Wave
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Seismic Waves and the Slinky
óSlinky demonstrations of ¡P-waves ¡S-waves ¡Surface waves óVIDEO óSeismic Slinky
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