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  • Other Sources  (6)
  • GEOPHYSICS  (6)
  • 1
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    1960 Chile - New estimate of polar motion excitation (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A recent reanalysis of the International Latitude Serivce (ILS) polar motion data-day has been processed using Kalman filtering techniques to generate the polar motion excitation function over the time-span from 1960 to 1965. The resulting excitation function has been examined for the effects of 1960 Chile in an attempt to determine experimentally how large earthquake affect polar motion. The resulting upper bound of about 75 x 10 to the 22nd N-m for a 10-deg dip (about 36 x 10 to the 22nd N-m for 20-deg dip) is consistent with results obtained from previous seismic studies, including a recent normal mode excitation result. Following future great earthquakes, monitoring of polar motion by space-based techniques such as VLBI should continue at high temporal resolution for several weeks in order to directly measure the rheological parameters of the upper mantle.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 16; 1193-119
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  • 2
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    Secular variation of earth's gravitational harmonic J2 coefficient from Lageos and nontidal acceleration of earth rotation (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Analysis of 5.5 years of Lageos satellite range data reveal significant residual nodal signatures: an acceleration and annual and semiannual periods. These signatures primarily reflect variations in the zonal gravitational harmonic J2 coefficient and hence the polar moment of inertia. The implied decrease of J2 = -3 x 10 to the -11th/yr is consistent with both historical observations of the nontidal acceleration of the earth's rotation and models of viscous rebound of the solid earth from the decrease in load due to the last deglaciation.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 303; June 30
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  • 3
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    Short period tidal variations of earth rotation (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is explained that the tidal deformation of the earth's polar moment of inertia by the moon and sun cause periodic variations in rotation. The short period oscillations give rise to a meter-sized, diurnal signature in the lunar laser ranging data obtained at McDonald Observatory. A solution is given for the scale parameter k/C at fortnightly and monthly tidal frequencies. The results are compared with those obtained by other investigators and with a theoretical estimate which includes the effect of oceans and a decoupled fluid core.
    Keywords: GEOPHYSICS
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  • 4
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    Tidal variations of earth rotation (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The periodic variations of the earths' rotation resulting from the tidal deformation of the earth by the sun and moon were rederived including terms with amplitudes of 0.002 millisec and greater. The series applies to the mantle, crust, and oceans which rotate together for characteristic tidal periods; the scaling parameter is the ratio of the fraction of the Love number producing tidal variations in the moment of inertia of the coupled mantle and oceans (k) to the dimensionless polar moment of inertia of the coupled moments (C). The lunar laser ranging data shows that k/C at monthly and fortnightly frequencies equals 0.99 + or - 0.15 and 0.99 + or - 0.20 as compared to the theoretical value of 0.94 + or - 0.04.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; Feb. 10
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  • 5
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    Improved analytic nutation model (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Models describing the earth's nutations are discussed. It is found that the simple model of Sasao et al., (1981) differs from Wahr's (1981) theory term by term by less than 0.3 marcsec if a modern earth structure model is used to evaluate the nutation structure constants. In addition, the effect of oceans is estimated.
    Keywords: GEOPHYSICS
    Type: IAU Symposium on the Impace of VLBI on Astrophysics and Geophysics; May 10, 1987 - May 15, 1987; Cambridge, MA; United States
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  • 6
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    Deep mantle viscous structure with prior estimate and satellite constraint (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A radially stratified and incompressible earth model with secular variation of the second degree gravity field J-dot(2) is used here to test sensitivity of data to viscosity increases with depth and convective boundary layer structure. Prior estimates and observed nontidal J-dot(23)(-C-dot(20)) are consistent with a layered lower mantle viscosity. Details of this layering are examined by comparing predicted and observed J-dot(3), J-dot(4). Speculation that a high-velocity layer exists above D-double prime is considered. With a 650-km thick deep high-viscosity layer, the remaining lower mantle is in one of two ranges: 1.5 to 3.5 x 10 exp 20 or 3.5 to about 10 exp 22 Pa s.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; B3; p. 4579-4609.
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