Exploration of Anisotropy from Crystal to Whole-Earth Scales
Description:
Evidence of seismic anisotropy is widespread within the Earth, including individual crystals, laboratory rock samples, borehole data, active-source seismic data, and global seismic data. The anisotropy of a material describes how wave speeds vary as a function of direction, and it is characterized by density and a 21-parameter symmetric 6 x 6 matrix that maps strain to stress. The space of 21-parameter elastic maps is vast and poses challenges for understanding and for practical applications based on laboratory or field data. Most seismologists assume a high-symmetry (low-parameter) version of Earth, either in the form of isotropy (2 parameters), vertical transverse isotropy (radial anisotropy: 5 parameters), or horizontal transverse isotropy (azimuthal anisotropy: 6 parameters). We offer a general approach to explore the space of elastic maps by starting with any given elastic map T having any type of symmetry, represented by Sigma: trivial, monoclinic, orthorhombic, tetragonal, transverse isotropic, isotropic, cubic, and trigonal. Using a combined minimization and projection procedure, we calculate the closest-Sigma maps to T, which results in 8 maps that can be visualized by a lattice of spheres representing the maps. The pathway from T to its closest-isotropic map can be obtained either by discretizing the direct path or by traversing a sequence of lattice nodes, such as trivial to monoclinic to orthorhombic to tetragonal to transverse isotropic to isotropic. We apply this approach to 21-parameter elastic maps derived from laboratory measurements of minerals, including dependencies on pressure and temperature. We also re-examine a global model of the D" region represented by 21-parameter elastic maps derived from geochemistry and rheology principles. The two primary advantages of this approach are 1) to provide visualization of elastic maps along specific pathways and 2) to offer distinct options for reducing the complexity of a given elastic map by obtaining a map that is closer to isotropic.
Session: Anisotropy Across Scales [Poster Session]
Type: Poster
Date: 5/3/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Aakash
Student Presenter: Yes
Invited Presentation:
Authors
Aakash Gupta Presenting Author Corresponding Author agupta7@alaska.edu University of Alaska Fairbanks |
Carl Tape ctape@alaska.edu University of Alaska Fairbanks |
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Exploration of Anisotropy from Crystal to Whole-Earth Scales
Session
Anisotropy Across Scales