Translations:Useful attenuation mechanisms/32/en

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When it comes to absorption, a basic assumption is made. When a wave travels one wavelength, absorption reduces the wave’s amplitude by a certain fraction. The assumption is that the fraction is independent of the wavelength. The absorption can be approximated as an exponential decay of energy with propagation distance. The decay is roughly constant with each frequency cycle. A high-frequency 39-Hz wave traveling at 3048 m/s has a wavelength of 78 m. A low-frequency 19.5-Hz wave traveling at 3048 m/s has a wavelength of 156 m. The high-frequency wave suffers the same amount of absorption by traveling 78 m as the low-frequency wave does in traveling 156 m, or twice the distance. The net result is that high-frequency components suffer greater attenuation than do low-frequency components per unit distance traveled. Absorption is measured by the quality factor Q. A weathered rock at the surface can have a Q factor as low as 10 or 20, whereas a deep, less-absorptive rock can have a Q factor of 200. That is, Q increases and absorption decreases with depth.