Thesis seminar: Seismic anisotropy – Niels Bohr Institute - University of Copenhagen

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Thesis seminar: Seismic anisotropy

Navn: Mariann Richterhausen

Seismic anisotropy occurs when elastic waves vibrating or travelling in one direction travel faster than another. It can be caused by 1) thin layers of otherwise isotropic material with different velocities or aligned heterogeneities, 2) aligned, fluid-filled fractures or cracks, and 3) aligned anisotropic minerals.
Today most seismological modelling still assumes isotropic conditions in the Earth. In reality, though, all materials are anisotropic and the line between anisotropy and isotropy is one of the resolution of available instrumentation. Even if minerals display strong anisotropy at the microscopic scale, the macroscopic medium can appear isotropic if the relative orientations of symmetry axes in the different crystals counteract in destroying the intrinsic anisotropy of each mineral.
Perhaps one of the most easily observable evidences of anisotropy is shear wave splitting, where the two orthogonally polarized quasishear waves travel with different wave speeds. It has been detected from both crustal and upper mantle anisotropy and can be characterized by the splitting parameters (δt; delay time between fast and slow polarization and Φ; the direction of the fast split wave). As a specific example of detection of anisotropy, the lecture will present results from the measurement of azimuthal anisotropy across the Sorgenfrei-Tornquist Zone from shear wave splitting based on data from the TOR-project.
The lecture will be given in Danish!

Vejleder: Søren Gregersen