Stephen BELLER
3D imaging of seismic anisotropy by inversion of complete teleseismic waveforms
Supervisor:
Sébastien Chevrot, GET Toulouse
Abstract
One of the major open questions in geodynamics is related to the distribution of deformation in the mantle. Seismic anisotropy holds the key to address this problem, but imaging anisotropy with a fine spatial resolution remains challenging. We have tackled the problem with a new approach based upon full waveform of teleseismic waveforms. The idea is to exploit the whole information contained in seismic waveforms, and not only shear wave Another important idea is that we no longer consider simplified description of anisotropy, such as for example the three Thomsen parameters that describe an hexagonal elasticity tensor nor impose particular orientation of symmetry axes (e.g. horizontal or vertical).
Instead, we invert for the 21 elastic coefficients of the fourth-order elasticity tensor. After inversion, the elasticity tensor at each node of the tomographic grid is analyzed to determine the orientation of the symmetry axes and extract the hexagonal part of the tensor. The figure shows the results of a synthetic experiment in which we have inverted a set of P, S, and SKS waves recorded by a regular array of stations spaced by 25 km at the surface. The inversion allows us to recover both the exact geometry of the cubic shape anisotropy anomaly. It also nicely recovers both the azimuth and dip of the main symmetry axis in the anisotropic domain, a remarkable achievement which is clearly beyond the reach of all the other classic tomographic approaches.
Probing depth and lateral variations of upper-mantle seismic anisotropy from full-waveform inversion of teleseismic body-waves
Probing depth and lateral variations of upper-mantle seismic anisotropy from full-waveform inversion of teleseismic body-waves
Beller, S. and Chevrot, S. (2020). Probing depth and lateral variations of upper-mantle seismic anisotropy from full-waveform inversion of teleseismic body-waves, Geophysical Journal International, 222, 352-387
keywords: Anisotropy, Full-waveform inversion, Lithosphere, Teleseismic dat