How to relate body wave and surface wave anisotropy?

Seismic anisotropy is one of the most efficient geological and geodynamical tools fur understanding the dynamics of the Earth. Upper mantle anisotropy is evident in seismic data sets for the last 30 years primarily from surfa ce wave dispersion curves and body wave SKS data. We demonstrate in this pa per that surface wave and body wave derived anisotropy can be explained by the same anisotropic parameters (L, G(c), G(s)) in the simplest case of a h orizontal fast symmetry axis. One application of this method is to display the SKS delay time and the corresponding azimuth, which can be derived from surface wave global (with a lateral resolution of around 2000 km) and regi onal (lateral resolution of 350 km) anisotropy tomography. A global-scale c omparison is disappointing since there are only a few areas where both data types are correctly retrieved at the same spatial scale (same Lateral reso lution). The anisotropy is well resolved in oceanic basins from surface wav es, whereas most measurements of SKS splitting are available below continen ts. However, there is a good agreement between surface wave and body wave a nisotropy in regions where large-scale processes (primarily tectonic) are t aking place, such as the western United States and in central Asia. In part icular, we show that, at high frequency (> 1 Hz), the observed SKS delay ti me and azimuth depend on the order in which S waves propagate through the l ayers. A comparison between synthetic and observed SKS phases in central As ia highlights the varying sensitivity of SKS waves at depth. We can obtain a good correlation between synthetic and observed SKS By considering anisot ropy only between 80 and 200 km depth in the tomographic model, rather than in the entire upper mantle. However, it is more difficult to explain the d iscrepancy between synthetic and observed SKS under the eastern United Stat es, where a large-scale coherent SKS anisotropy is present, Such results ca ll for more sophisticated SKS waveform modeling and for enhanced lateral re solution in anisotropic tomographic models.