Upper mantle anisotropy: evidence from free oscillations

Summary Isotropic earth models are unable to provide uniform fits to the gross Earth normal mode data set or, in many cases, to regional Love-and Rayleigh-wave data. Anisotropic inversion provides a good fit to the data and indicates that the upper 200km of the mantle is anisotropic. The nature and magnitude of the required anisotropy, moreover, is similar to that found in body wave studies and in studies of ultramafic samples from the upper mantle. Pronounced upper mantle low-velocity zones are characteristic of models resulting from isotropic inversion of global or regional data sets. Anisotropic models have more nearly constant velocities in the upper mantle.
Normal mode partial (Frediét) derivatives are calculated for a transversely isotropic earth model with a radial axis of symmetry. For this type of anisotropy there are five elastic constant. The two shear-type moduli can be determined from the toroidal modes. Spheroidal and Rayleigh modes are sensitive to all five elastic constants but are mainly controlled by the two compressional-type moduli, one of the shear-type moduli and the remaining, mixed-mode, modulus. The lack of sensitivity of Rayleigh waves to compressional wave velocities is a characteristic only of the isotropic case. The partial derivatives of the horizontal and vertical components of the compressional velocity are nearly equal and opposite in the region of the mantle where the shear velocity sensitivity is the greatest. The net compressional wave partial derivative, at depth, is therefore very small for isotropic perturbations. Compressional wave anisotropy, however, has a significant effect on Rayleigh-wave dispersion. Once it has been established that transverse anisotropy is important it is necessary to invert for all five elastic constants. If the azimuthal effect has not been averaged out a more general anisotropy may have to be allowed for.     

Centroid-moment tensor solutions for October–December, 1983

Centroid-moment tensor solutions are presented for 133 earthquakes that occurred during the fourth quarter of 1983.     

Centroid-moment tensor solutions for July–September, 1984

Centroid-moment tensor solutions are presented for 197 earthquakes that occurred during the third quarter of 1984. The solutions are obtained using corrections for aspherical Earth structure.     

Parameterization of a spherically symmetrical earth model with special references to the upper mantle

The advantages of using relatively simple polynomial parameterizations of the velocities and density within the earth in inversions of the free oscillation and travel time data set are discussed with special reference to the development of a standard earth model.     

Lunar penumbral eclipses, 1900–2200

A complete survey of past and future penumbral eclipses of the Moon is presented in a tabular form. It contains details of the circumstances of 257 eclipses as seen from the geographical location of Warsaw.     

Lunar eclipses in Europe, 900–2200

A complete survey of past and future umbral eclipses of the Moon visible in Europe is presented in a tabular form. It contains full details of the local circumstances of 1705 eclipses for the geographical location of Warsaw (Poland). Of these, 502 end or begin 0 to 25.5 degrees below the astronomical horizon at Warsaw, thus are observable only at other European places. A set of simple formulae is given that allows to calculate the local circumstances for arbitrary location. A new simple and accurate algorithm to compute the times of contacts, which is based on a solution on a sphere instead of on a tangent plane, thus without the use of the Besselian elements, is presented.     

Evolutionary Status of Late-type Contact Binaries: Case of a 1.2+1 M ⊙ Binary

It is argued that typical W UMa-type stars are old, advanced evolutionary objects, similar to Algols, in the sense that they are past mass exchange resulting in a mass ratio inversion. Their secondaries are oversized due to depletion of hydrogen, and in many cases they possess small helium cores. An alternative evolutionary scenario leading to such a configuration is presented. Differences between the evolution of binaries with the initial mass ratio far and close to unity are discussed.