3D Radial and Azimuthal Anisotropy Structure in North America
We recently developed a 3D tomographic model of the upper mantle beneath North America that includes both isotropic S velocity structure as well as radial and azimuthal anisotropy (Marone et al., 2007; Marone and Romanowicz, 2007). This model was constructed from a joint inversion of fundamental and higher mode surface waveforms together with constraints on azimuthal anisotropy derived from SKS splitting measurements. This model showed evidence for the presence of two layers of anisotropy beneath the stable part of the North American continent: a deeper layer with Vsh>Vsv and with the fast axis direction aligned with the absolute plate motion direction suggesting lattice preferred orientation of anisotropic minerals in a present day asthenospheric flow and a shallower lithospheric layer likely showing records of past tectonic events. Under the tectonically active western US, where the lithosphere is thin, the direction of tomographically inferred anisotropy is stable with depth and compatible with the absolute plate motion direction. We here present an updated model, which includes a larger waveform data set (three more years of data including new data from US Array) and a larger SKS splitting dataset. In addition, we are going one step further in that we now combine the results from inversion for radial and azimuthal anisotropy, to recover the distribution of the direction and amplitude of the fast axis in 3D, under the assumptions of hexagonal symmetry. We discuss the results in the light of possible causes of anisotropy in the cratonic lithosphere.
H. Yuan et al., "3D Radial and Azimuthal Anisotropy Structure in North America," Eos, Transactions American Geophysical Union, vol. 88, no. 52, American Geophysical Union (AGU), Dec 2007.
AGU Fall Meeting (2007: Dec. 10-14, San Francisco, CA)
Geosciences and Geological and Petroleum Engineering
Keywords and Phrases
Mantle; Surface waves and free oscillations; Tomography; Dynamics of lithosphere and mantle: general
Article - Conference proceedings
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