Elastic anisotropy of layered or cracked media: alternative parameterisation

Adamus, Filip Piotr (2021) Elastic anisotropy of layered or cracked media: alternative parameterisation. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (9MB)

Abstract

This thesis consists of six research papers. Each of them attempts to contribute to the field of elastic anisotropy. We investigate layered or cracked materials in the context of micromechanics and seismology. In the document, we discuss three following topics. In the first part, we study the overall (effective) elastic properties of a medium that is longwave equivalent to thin and parallel layers. To obtain the effective elasticity, we use the Backus average. Initially, we consider a typical scenario of isotropic layers that result in a transversely isotropic medium. We propose an alternative parameter that describes the anisotropy of such an effective material. We use it to indicate the presence of fluid within thin layers. Further, we discuss a crucial mathematical approximation of the Backus average and examine a particular case in which the approximation is inaccurate. This time, we allow the layers to exhibit lower symmetry than the isotropic one. In the second part, we consider an orthotropic symmetry, which is a good analogy to a cracked material. Instead of discussing the medium’s microstructure, we focus on the effective properties only. Specifically, we investigate the relations among orthotropic stiffnesses in the context of primary-wave phase velocity. We introduce the so-called cumulative moduli to describe the dependence of quasi P-wave velocity on each elasticity parameter. Such a parameterisation is useful for the velocity approximation. In the last part, we analyse cracked media in the context of both micromechanics and seismology. We propose an alternative way of obtaining effective elastic properties of a material with many parallel cracks. We represent a set of cracks by a thin layer embedded in a background medium, using Backus average; hence, we generalise the linear-slip method. Finally, we study the influence of cracks on the azimuthal variations of amplitude. We present patterns consisting of a series of azimuthal shapes that change with increasing concentration of inhomogeneities.

Actions (login required)

View Item