Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008geoji.175..116c&link_type=abstract
Geophysical Journal International, Volume 175, Issue 2, pp. 116-134.
Astronomy and Astrophysics
Astronomy
5
Composition Of The Mantle, Elasticity And Anelasticity, Surface Waves And Free Oscillations, Seismic Attenuation
Scientific paper
Thermally activated, viscoelastic relaxation of the Earth's materials is responsible for intrinsic attenuation of seismic waves. Seismic observations have been used to define layered radially symmetric attenuation models, independent of any constraints on temperature and composition. Here, we interpret free-oscillation and surface wave attenuation measurements in terms of physical structures, by using the available knowledge on the physical mechanisms that govern attenuation at upper-mantle (<400km) conditions. We find that observations can be explained by relatively simple thermal and grain-size structures. The 1-D attenuation models obtained do not have any sharp gradients below 100km, but fit the data equally well as the seismic models. The sharp gradients which characterize these models are therefore not required by the data.
In spite of the large sensitivity of seismic observations to temperature, a definitive interpretation is limited by the unknown effects of pressure on anelasticity. Frequency dependence of anelasticity, as well as trade-offs with deeper attenuation structure and dependence on the elastic background model, are less important. Effects of water and dislocations can play an important role as well and further complicate the interpretation. Independent constraints on temperature and grain size expected around 100km depth, help to constrain better the thermal and grain-size profiles at greater depth. For example, starting from a temperature of 1550K at 100km and assuming that the seismic attenuation is governed by the Faul & Jackson's (2005) mechanism, we found that negative thermal gradients associated with several cm grain sizes (assuming low activation volume) or an adiabatic gradient associated with ~1cm grain size, can explain the data. A full waveform analysis, combining the effects on phase and amplitude of, respectively, elasticity and anelasticity, holds promise for further improving our knowledge on the average composition and thermal structure of the upper mantle.
Cammarano Fabio
Romanowicz Barbara
No associations
LandOfFree
Radial profiles of seismic attenuation in the upper mantle based on physical models does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Radial profiles of seismic attenuation in the upper mantle based on physical models, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radial profiles of seismic attenuation in the upper mantle based on physical models will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1701119