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12-10-2010, 02:40 PM
Seismic Waves.ppt (Size: 333.5 KB / Downloads: 129)
What is a wave, types of waves
Measure a wave
Wave speed, period, wavelength, amplitude
Ray path, reflection, refraction, diffraction
Types of seismic waves
P and S waves; body waves and surface waves
Identify different waves by their arrival times, amplitudes and periods.
What is a Wave ?
A wave is a disturbance or variation that transfers energy progressively from point to point in a medium.
Sound wave: variation of pressure in the air
Radio wave: variation of EM intensity
Water wave: variation of water surface
Seismic wave: variation of elastic deformation in rocks
Note that the medium doesn’t travel along with the wave.
Waves like the EM wave do not even need a medium to propagate.
It is the speed that the wave travels.
The wave speed is a material property. No matter how big the wave is, it travels at the same speed.
Sound wave speed in dry air v = 331 + 0.6 T (m/s)where T is temperature in Celsius
Elastic wave speeds in rocks are 1 ~ 10 km/s, depends mainly upon temperature, pressure, and composition.