Seismology Measuring the Interior
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Transcript of Seismology Measuring the Interior
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Solid Earth Geophysics
Ali [email protected].
saDepartment of Earth SciencesKFUPM
Today’s class: Seismology Measuring the InteriorReading: Fowler Chapter 4
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Body and surface waves
Earthquake’s energy is transmitted through the earth as seismic waves according to the wave equation.
Two types: Body waves - transmit energy through earth’s interior
Primary (P) wave- rocks vibrate parallel to direction of wave; compression and expansion (slinky example)- irrotatational waves
Secondary (S) wave- rocks move perpendicular to wave direction; rock shearing (rope-like or ‘wave’ in a stadium)- rotational waves
Surface waves - transmit energy along earth’s surface Love waves: rock moves from side to side like snake Rayleigh waves: rolling pattern like ocean wave
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Primary WavesPrimary Waves Secondary WavesSecondary Waves
Body Waves
Dilatation and No Rotation Rotation and no change in volume
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P-waveP-wave S-waveS-wave
Animations: Body Waves
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Movement of EarthMovement of Earth
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3D Components of Waves
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3D Components
6.27P-waveP-wave S-waveS-wave 6.35
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Snell's law
When velocity increases in next layer, ray gets bent away from normal on layer
In earth, velocities increase throughout the mantle
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Types of Surface Waves
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Rayleigh Waves
Typical velocity: ~ 0.9 that of the S wave
Behavior: Causes vertical together with back-and-forth horizontal motion. Motion is similar to that of being in a boat in the ocean when a swell moves past.
Arrival: They usually arrive last on a seismogram.
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Love Waves
Typical velocity: Depends on earth structure (dispersive), but less than velocity of S waves.
Behavior: Causes shearing motion (horizontal) similar to S waves.
Arrival: They usually arrive after the S wave and before the Rayleigh wave.
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Amp ~ 1/x
Amplitudes of waves
Body WaveBody Wave Surface WaveSurface Wave
Amp ~ x-1/2
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