Shear (geology)

Abstract: A complete suite of closed analytical expressions is presented for the surface displacements, strains, and tilts due to inclined shear and tensile faults in a half-space for both point and finite rectangular sources. These expressions are particularly compact and free from field singular points which are inherent in the previously stated expressions of certain cases. The expressions derived here represent powerful tools not only for the analysis of static field changes associated with earthquake occurrence but also for the modeling of deformation fields arising from fluid-driven crack sources.

Abstract: A complete set of closed analytical expressions is presented in a unified manner for the internal displacements and strains due to shear and tensile faults in a half-space for both point and finite rectangular sources. These expressions are particularly compact and systematically composed of terms representing deformations in an infinite medium, a term related to surface deformation and that is multiplied by the depth of observation point. Several practical suggestions to avoid mathematical singularities and computational instabilities are also presented. The expressions derived here represent powerful tools both for the observational and theoretical analyses of static field changes associated with earthquake and volcanic phenomena.

Abstract: A theory is presented for the plastic deformation of metallic glasses below their glass transition temperature. The theory is based on two modes of thermally activated shear transformations initiated around free volume regions under an applied shear stress. The regions are typically conceived to be about 5 atom diameters across. At high temperatures (0.6 Tg ≲ T ≲ Tg) the transformation is a diffuse rearrangement producing a relatively small local shear strain in a roughly spherical region. At low temperatures (0 < T ≲ 0.6 Tg) the transformation is in a narrow disk shaped region and resembles closely the nucleation of a dislocation loop. The theory is in good accord with experimental observations. Based on the theory, possible levels of flow dilatation have been computed from which rates of shear localization can be obtained. At low temperatures, very rapid shear localization is predicted which is in good accord with the observations reported in the literature and with recent cinematographic observations.