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Benjamin F Chao – One of the best experts on this subject based on the ideXlab platform.

  • solid pole tide in global gps and superconducting gravimeter observations signal retrieval and inference for mantle Anelasticity
    Earth and Planetary Science Letters, 2017
    Co-Authors: Hao Ding, Benjamin F Chao
    Abstract:

    Abstract The mantle Anelasticity plays an important role in Earth’s interior dynamics. Here we seek to determine the lower-mantle Anelasticity through the solution of the complex Love numbers at the Chandler wobble period. The Love numbers h 21 , l 21 , δ 21 and k 21 are obtained in the frequency domain by dividing off the observed polar motion, or more specifically the pole tide potential, from the observed GPS 3-D displacement field and SG gravity variation. The latter signals are obtained through the array processing method of OSE (optimal sequence estimation) that results in greatly enhanced signals to be extracted from global array data. The resultant Love number estimates h 21 = 0.6248 ( ± 5 e − 4 ) − 0.013 ( ± 5 e − 3 ) i , l 21 = 0.0904 ( ± 8 e − 4 ) − 0.0008 ( ± 2 e − 3 ) i , δ 21 = 1.156 ( ± 2 e − 3 ) − 0.003 ( ± 1 e − 3 ) i and k 21 = 0.3125 ( ± 2 e − 3 ) − 0.0069 ( ± 3 e − 3 ) i are thus well-constrained in comparison to past estimates that vary considerably. They further lead to estimates of the corresponding mantle anelastic parameters f r and f i , which in turn determines, under the single-absorption band assumption, the dispersion exponent of α = 0.21 ± 0.02 with respect to the reference frequency of 5 mHz. We believe our estimate is robust and hence can better constrain the mantle Anelasticity and attenuation models of the Earth interior.

  • long period variations in gravity field caused by mantle Anelasticity
    Journal of Geophysical Research, 1996
    Co-Authors: Yaozhong Zhu, C K Shum, M K Cheng, Byron D Tapley, Benjamin F Chao
    Abstract:

    A numerical perturbation approach is used to assess the effect of mantle Anelasticity on the Earth’s zonal response coefficient :, the zonal geopotential coefficient J2, and the orbital node of geodetic satellites. The theoretical predictions are used to compare solutions of elastic ocean tide models and tides observed by geodetic satellites for Mr, M m , Ssa, and S a . The discrepancies between the satellite observed tides and the solution from Schwiderski and recent altimetric ocean tide models can be partly explained by the predicted effect of mantle anelasti- city at Mf and M m frequencies. Approximately 80% of the observed semiannual variation in &/2 by geodetic satellites can be attributed to the tidal deformation from Anelasticity and from the classical equilibrium ocean. The predicted : for the 18.6-year tide was computed for an Earth with an anelastic mantle and a nonequilibrium ocean. The range of the lower and upper bounds of : for the 18.6-year tide is from 0.345 to 0.377 in amplitude, and from-6 o to 3 o in phase, with preferred amplitude of 0.365 and phase of-0.o8.

Mgd Marc Geers – One of the best experts on this subject based on the ideXlab platform.

  • on the underlying micromechanisms in time dependent Anelasticity in al 1 wt cu thin films
    Acta Materialia, 2017
    Co-Authors: Lijc Lambert Bergers, Jpm Johan Hoefnagels, Mgd Marc Geers
    Abstract:

    This paper reveals potential micro mechanisms underlying time-dependent Anelasticity observed in Al-(1 wt%)Cu thin films. The analyzed deformation mechanisms involve dislocation motion and interaction with solute diffusion, grain boundaries and precipitates. In order to investigate the role of these mechanisms, Al-(1 wt%)Cu alloy thin films are heat treated to systematically change the precipitation state, while characterizing the grain boundary distribution with electron backbackscatterfraction. Micromechanical characterization is performed by microbeam bending, nano-tensile creep testing and nano-indentation. Results in microbeam bending reveal, for all precipitate and grain boundary states considered, a similar time-dependent evolution of the anelastic strain after load release. The magnitude of the recovered strain is also observed to be independent of the precipitate or grain boundary configuration. The nano-tensile creep test also indicates the same time-dependent anelastic evolution, indicating that the loading state does not affect the underlying mechanisms. Analysis of strain bursts in nano-indentation shows that pinning of dislocations by Cu solutes is unaffected by the precipitation state. Based on uniaxial creep and time-dependent Anelasticity measurements in pure Al specimens, it is made plausible that the time-dependent Anelasticity originates from diffusion-limited glide or climb of dislocation segments that are pinned at Cu solutes or in dislocation structures, which provide an internal driving force.

Don L Anderson – One of the best experts on this subject based on the ideXlab platform.

  • the Anelasticity of the mantle
    Geophysical Journal International, 2010
    Co-Authors: Don L Anderson
    Abstract:

    The attenuation of seismic waves provides the most direct data regarding the non-elastic properties of the Earth. Recent experimental results from body waves, surface waves and free oscillations provide estimates of the Anelasticity in various regions of the Earth. Results to date show that the upper mantle is more attenuating than the lower mantle, the maximum attenuation is in the vicinity of the low-velocity zone, a rapid increase in attenuation occurs in the vicinity of the C-region of the mantle and compressional waves are less attenuated than shear waves. A frequency dependence of Q has not yet been discovered. Most laboratory measurements of attenuation have been performed at ultrasonic frequencies on pure specimens of metals, glasses, plastics and ceramics. A general feature of laboratory measurements is an exponential increase of attenuation with temperature on which are superimposed peaks which can be attributed to dislocation or other defect phenomena. Measurements on natural rocks at atmospheric pressure can be attributed to the presence of cracks. The intrinsic attenuation of rocks as a function of temperature and pressure is not known. However, on other materials grain boundary phenomena dominate at high temperature. This can be attributed to increased grain boundary mobility at high temperatures. High pressure would be expected to decrease this mobility. If attenuation in the mantle is due to an activated process it is probably controlled by the diffusion rate of defects at grain boundaries. Estimates of attenuation in the lower mantle then yield an estimate of the activation volume of the defects contributing to the loss. If the lower mantle is assumed homogeneous the estimated activation volume is a small fraction of the presumed molal volume of materials making up the lower mantle. Stress induced migration of small point defects is a possible loss mechanism consistent with the observations.

Arwen Deuss – One of the best experts on this subject based on the ideXlab platform.

  • normal mode splitting function measurements of Anelasticity and attenuation in the earth s inner core
    Geophysical Journal International, 2013
    Co-Authors: Anna M. Mäkinen, Arwen Deuss
    Abstract:

    We have used the iterative spectral fitting method to measure both the elastic and anelastic splitting functions of 20 inner core sensitive normal modes. These modes show significant improvement in spectral fit when anelastic splitting function coefficients dst are introduced in addition to the elastic splitting function coefficients cst. We employ two separate anelastic treatments: (i) fully anelastic measurement, in which a complete set of anelastic splitting function coefficients is measured in addition to the elastic coefficients, and (ii) zonal anelastic measurement, in which Anelasticity is only allowed in zonal splitting function coefficients. Together, these two approaches confirm that normal modes sensitive to the Earth’s inner core resolve zonally dominant elastic and anelastic structures. The zonal dominance of Anelasticity suggests that the inner core exhibit cylindrical attenuation anisotropy in addition to cylindrical velocity anisotropy. In particular, the zonally dominant Anelasticity correlates with zonal elastic structure, that is, directions of higher velocity in the inner core also appear more attenuating.

  • Normal mode splitting function measurements of Anelasticity and attenuation in the Earth’s inner core
    Geophysical Journal International, 2013
    Co-Authors: Anna M. Mäkinen, Arwen Deuss
    Abstract:

    We have used the iterative spectral fitting method to measure both the elastic and anelastic splitting functions of 20 inner core sensitive normal modes. These modes show significant improvement in spectral fit when anelastic splitting function coefficients dst are introduced in addition to the elastic splitting function coefficients cst. We employ two separate anelastic treatments: (i) fully anelastic measurement, in which a complete set of anelastic splitting function coefficients is measured in addition to the elastic coefficients, and (ii) zonal anelastic measurement, in which Anelasticity is only allowed in zonal splitting function coefficients. Together, these two approaches confirm that normal modes sensitive to the Earth’s inner core resolve zonally dominant elastic and anelastic structures. The zonal dominance of Anelasticity suggests that the inner core exhibit cylindrical attenuation anisotropy in addition to cylindrical velocity anisotropy. In particular, the zonally dominant Anelasticity correlates with zonal elastic structure, that is, directions of higher velocity in the inner core also appear more attenuating.

Lijc Lambert Bergers – One of the best experts on this subject based on the ideXlab platform.

  • on the underlying micromechanisms in time dependent Anelasticity in al 1 wt cu thin films
    Acta Materialia, 2017
    Co-Authors: Lijc Lambert Bergers, Jpm Johan Hoefnagels, Mgd Marc Geers
    Abstract:

    This paper reveals potential micro mechanisms underlying time-dependent Anelasticity observed in Al-(1 wt%)Cu thin films. The analyzed deformation mechanisms involve dislocation motion and interaction with solute diffusion, grain boundaries and precipitates. In order to investigate the role of these mechanisms, Al-(1 wt%)Cu alloy thin films are heat treated to systematically change the precipitation state, while characterizing the grain boundary distribution with electron backscatter diffraction. Micromechanical characterization is performed by microbeam bending, nano-tensile creep testing and nano-indentation. Results in microbeam bending reveal, for all precipitate and grain boundary states considered, a similar time-dependent evolution of the anelastic strain after load release. The magnitude of the recovered strain is also observed to be independent of the precipitate or grain boundary configuration. The nano-tensile creep test also indicates the same time-dependent anelastic evolution, indicating that the loading state does not affect the underlying mechanisms. Analysis of strain bursts in nano-indentation shows that pinning of dislocations by Cu solutes is unaffected by the precipitation state. Based on uniaxial creep and time-dependent Anelasticity measurements in pure Al specimens, it is made plausible that the time-dependent Anelasticity originates from diffusion-limited glide or climb of dislocation segments that are pinned at Cu solutes or in dislocation structures, which provide an internal driving force.