## Abstract

The nature of short-term mantle rheology for timescales between the seismic frequency band and a few hundred years remains relatively unknown. We have made use of two pieces of information, which have emerged as a consequence of the recent acquisition of data from the LAGEOS satellite, to place some contraints on the rheological parameters of short-term mantle rheology. The first is the secular variation of the gravitational harmonic J ̇. The second is the amount of dispersion of the tidal Love number for the 18.6 y tide, which has been inferred to be ∼ 20%. Two types of rheology have been considered. The first is a frequency-dependent Q rheology. An analytical expression for the transformed shear modulus has been developed from the truncated retardation spectrum explicitly for this purpose. The second anelastic rheology we have used is a standard linear solid, where the parameters of importance are the relaxation strength Δ and the short-term viscosity ν_{2}. Rheological parameters of the frequency-dependent Q model previously proposed by Lambeck and Nakiboglu to explain the dispersion of the tidal Love number for a 18.6 y period are found to produce too much dispersion for the Chandler wobble and to yield seismic Q's between O(10^{3}) and O(10^{4}) for fundamental toroidal modes, which are not compatible with the data. We have used instead a three-layer model consisting of an elastic lithosphere, a mantle with a standard-linear solid rheology whose Debye peak lies beyond the long time cutoff of the retardation spectrum, and an inviscid core. For relaxation strength of Δ around 1 and short-term viscosity ν_{2} < 10^{21} P unacceptably large rates of J ̇ would result from earthquake excitation. A sharp decrease of the tidal dispersion takes place for ν_{2} ≅ 5 × 10^{20} P and Δ = 1.0. For smaller values of relaxation strength, Δ = 0.15 the maximum tidal dispersion is only 9% and decreases gradually as ν_{2} is increased beyond 5 × 10^{20} P. We have found that the maximum dispersion caused by the Maxwell rheology is small, around 5%, even for asthenospheric viscosities of O(10^{18}P). These results suggest that the datum of 18.6 y tidal dispersion can be utilized eventually to place constraints on potential candidates of short term mantle rheology.

Original language | English (US) |
---|---|

Pages (from-to) | 235-249 |

Number of pages | 15 |

Journal | Physics of the Earth and Planetary Interiors |

Volume | 38 |

Issue number | 4 |

DOIs | |

State | Published - May 1985 |