Anisotropy and shear‐velocity heterogeneities in the upper mantle

Abstract

Abstract. Long-period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle. The dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure. The data are corrected for the effect of surface layers and both Love and Rayleigh waves are used. Shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km. The shear wave velocity distribution to 200 km depth correlates with surface tectonics, except in a few anomalous regions. Below that depth the correlation vanishes. Cold subducted material shows up weakly at 350 km as fast S-wave anomalies. In the transition region a large scale pattern appears with fast mantle in the South-Atlantic. S-anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones. The Pacific shows a NW-SE fabric.

Seismic properties of the upper mantle beneath Lanzarote (Canary Islands): Model predictions based on texture measurements by EBSD

“…Raitt et al, 1969;Forsyth, 1975;Nataf et al, 1984;Tanimoto and Anderson, 1985;Shearer and Orcutt, 1986;Montagner and Tanimoto, 1990;Silver and Chan, 1991) and laboratory experiments (e.g. Carter and Avé Lallemant, 1970;Nicolas et al, 1973;Kunze and Avé Lallemant, 1981;Chopra and Paterson, 1981;Zeuch and Green, 1984;Zhang and Karato, 1995;Tommasi et al, 1999;Zhang et al, 2000;Bystricky et al, 2000).…”

The RMS residual temperature in the convecting mantle and seismic heterogeneities.

“…The gravity and geoid measurements also indicate a possible temperature variation and deformation of the earth caused by the convection current (e .g., MCKENZIE, 1977;JARVIS and PELTIER , 1982). R ecent detailed global seismological studies on the lateral heterogeneity of seismic velocity (e.g., DZIEWONSKI , 1984;MASTERS et al, 1982;NATAF et al, 1984;WOODHOUSE and DZIEWONSKI , 1984) provide new insight about convection. They contain basically two kinds of three-dimensional information , that is, the magni- …”

Global mapping of the uppermantle by surface wave tomography

“…In general the perturbations across discontinuities is highly correlated. In both Nataf et al (1984Nataf et al ( , 1986 and Woodhouse and Dziewonski (1984) the character of the perturbations changes at 220 and 400 km:…”

“…Techniques have recently been developed to simultaneously invert data over many great cicle paths to obtain global maps of lateral heterogeneity (Nakanishi and Anderson, 1982, 1983a, b, 1984, Woodhouse and Dziewonski, 1984, (Fig. 1) azimuthal anisotropy (Tanimoto and Anderson, 1983, 1984, 1985 and polarization anisotropy (Nataf et al, 1984(Nataf et al, , 1986. Although the results are currently of relatively low resolving power they can be used to discuss the regional structure of the uppermantle on a scale which is comparable to the sizes of the plates and the characteristic lengths which are thought to be important in plate tectonics.…”

“…Upper Mantle Models Nataf et al (1984Nataf et al ( , 1986 inverted the data sets of Nakanishi and Anderson to obtain the lateral structure and polarization anisotropy of the mantle to depths of 670 km. The resolution of the data is best between about 200 and 400 km.…”