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Field and laboratory measurements of attenuation in metals, non-metals, and rocks over a wide range of frequencies indicate that the specific attenuation factor, 1/Q, is substantially independent of frequency in homogeneous material, whereas it varies as the first power of frequency in liquids. This suggests that the mechanism
An inversion method can be used to compute the intrinsic Q in shear of the earth's mantle from available data on attenuation of the surface waves and free oscillations. The restrictions and assumptions in the calculation are: (1) Q must be positive; (2) Q is assumed to be independent of frequency; and (3) the mechanism of energy dissipation is through a complex modulus.
The results show that, in shear, the upper mantle has a much higher attenuation than the lower mantle. Q for the upper mantle, from the surface to a depth of 650 km., is estimated at 110; for the lower mantle, below 650 km., it is much higher than this, but the exact value cannot be estimated with precision. There are indications of fine variations of Q in the upper mantle, but present accuracy of the data and the assumptions used do not permit the literal use of these indications. Partial melting in a low velocity layer at shallow depth is considered and a small amount of partial melting is not inconsistent with the above result and the data.
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