Principles of rock deformation and tectonics / Основы деформации горных пород и тектоники

Two words are used to describe the result of a stress: ‘deformation’ and ‘strain’. Deformation is a general term describing the change of shape, size and/or position of an object, while strain (or ‘internal’ deformation) is used when associated with some quantification of shape change. (Note that in French, deformation is used for both meanings.)
No stress, no deformation. Let us begin with deformation, which is the consequence of applying some stress. In the following section, however, symbols referring to a stress will naturally appear here and there. They name the principal directions of push (σ1) and pull (σ3). <...>