Our final goal is a 3D high resolution tomographic model incorporating both radial and azimuthal anisotropy. Starting from our 3D radial anisotropic structure, we have begun addressing the distribution of azimuthal anisotropy, for which we have extended our NACT formalism. Resolving azimuthal anisotropy's four different components will only be possible with the improved coverage we expect from the USArry data. Meanwhile, using appropriate scaling relationships for the upper mantle, we are developing a preliminary 3D model, which, in addition to the isotropic S-velocity structure and the anisotropic parameter , also incorporates the dominant 2- variations of anisotropy. Such a model can be interpreted in terms of an orthotropic medium, characterized by radial anisotropy with a symmetry axis of arbitrary orientation and described by the 5 Love parameters plus two angles defining the axis orientation. We hope to obtain constraints on the depth distribution of azimuthal anisotropy and in particular to discriminate between a lithospheric and an asthenospheric origin of the observed SKS splitting.
Berkeley Seismological Laboratory
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