Characterization of Elastic Tensors of Crustal Rocks with respect to Seismic Anisotropy

Raju, Anissha

Undergraduate Honors Thesis

Characterization of Elastic Tensors of Crustal Rocks with respect to Seismic Anisotropy Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/9k41zd86x

Abstract

A wide range of minerals are stable is the Earth’s crust. Minerals belong to one of the seven crystal systems and have a wide range of densities. Hence, evaluating crustal seismic anisotropy is very complicated. Seismic anisotropy does not only depend on the types of minerals present, but rather considers mineral orientation, which is greatly dependent on the presence of Lattice Preferred Orientation (LPO), within a rock body. This study aims to investigate mineralogical role in rocks’ anisotropy and anisotropy symmetry. Hence, over 100 elastic tensors of crustal rocks was compiled from published studies from all over the world, along with the composition, pressure and temperature conditions of the rock samples. These compiled rock samples are representative of the rock types seen in the lower crust. The elastic tensors were decomposed into different symmetry classes and η_K was calculated for each rock sample. η_K measures the deviation from a perfectly elliptical hexagonal phase velocity. The total rock anisotropy of these samples ranges from 1.27% to 25.47%. Some rock samples dominantly have hexagonal symmetry, while others have orthorhombic and lower symmetry class. Higher amounts of mica in rock samples correlate to a higher hexagonal component of anisotropy. Similarly, rock samples with higher amphibole content tends to have a higher orthorhombic component of anisotropy. It is also shown that rock samples with higher anisotropy have lower ηK value, majority of which are below 1. These trends will be useful in forward modelling studies involving crustal anisotropy.

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