ISSN:
1365-2478
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
,
Physics
Notes:
Laboratory measurements indicate that seismic absorbtion in sedimentary rocks lies in the range 0.1 to 1.0 decibel per wavelength. Field measurements on the amplitude attenuation of direct, reflected and refracted pulses give values consistent with this.If the absorption is linear, dispersion must occur. If it occurs field measurements show that it must be less than 1% over the frequency range 20 c/s to 20 kc/s.Seismic pulses broaden so slowly with distance that, if the absorbtion is linear it must be less than that measured in the laboratory by a factor of at least ten. This is inconsistent with the amplitude measurements and would mean that emplaced rocks are more perfectly elastic than steel.Seismic absorbtion must therefore be non-linear. It is assumed that, for large values of Q, the non-linear equation of motion may be linearised (Knopoff and MacDonald, 1958) and Fourier synthesis used. If this is valid, then the attenuation per unit distance must be practically independent of frequency and dispersion must be negligible.Whatever mechanism is acting it must produce an attenuation of roughly one decibel per 1000 feet and a pulse broadening of about 1–2% in the same distance.It is extremely desirable to make more field and laboratory experiments to determine the physical mechanism by which absorbtion takes place.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-2478.1961.tb01510.x
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