Inversions of high frequency Q-1{gamma}(f)

• Published in: Geophysical Journal International
• Main Author: Burton, Paul W.
• Format: Text
• Language: English
• Published: Oxford University Press 1977
• Subjects: Articles; Novaya Zemlya
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/48/1/29; https://doi.org/10.1111/j.1365-246X.1977.tb01283.x

The specific attenuation factor of Rayleigh waves in the Earth is a function of frequency Q−1γ ( f ): the data used here are already obtained from nuclear explosions at Novaya Zemlya and Southern Sinkiang within the highfrequency range 0.015–0.085 Hz. Depth distributions for the specific attenuation factors of shear and compressional body waves, Q−1 α,β ( Z ) which satisfy the amplitude attenuation data for Rayleigh waves are obtained from a simple half-space approximation, ad hoc model fitting, and finally by Hedgehog inversion. The simple half-space approximation and ad hoc model, fitting, which relate Q-1 α,β ( Z ) to the observed Q-1γ 0 ( f ), quickly indicate useful results. However, Hedgehog inversion is preferred because this gives profiles of Q−1α,β ( Z ) for anelasticity within the crust and uppermost mantle with a spread of acceptable values at each depth rather than a single line profile. Anelasticity of the Earth from Novaya Zemlya differs from the Southern Sinkiang sample. Profiles based on the Southern Sinkiang sample show little dissipation of seismic energy at depths around 40–75 km with Q−1 α about 0.001. With increasing depth there is an increase in lossiness to Q−1 α around 0.005 beneath 120 km. The data from Novaya Zemlya produce what may be regarded as a representative model of continental anelasticity. The crustal and lithospheric cap shows little dissipation with Q−1 α about 0.002. Beneath the lithospheric cap Q−1 α is about 0.007 and Q−1 α is about 0.015 showing a region of high dissipation coincident with the low-velocity zone, although low velocity is not assumed. These Q−1 α,β ( Z ) profiles are consistent with the hypothesis of a partial melt transition from the lithosphere to the asthenosphere, although this does not exclude alternative attenuation mechanisms.