# Translations:Dictionary:Elastic constants, elastic moduli/1/en

{{#category_index:E|elastic constants, elastic moduli}}
Elasticity deals with deformations that vanish entirely upon removal of the stresses that cause them. For small deformations, Hooke's law holds and strain is proportional to stress. The passage of a low-amplitude seismic wave is an example. The general elasticity tensor relating stress and strain can be expressed as a matrix equation (Figure H-7). In anisotropic media this tensor possesses up to 18–21 independent constants. In **transversely isotropic media** (where properties are the same measured in two orthogonal directions but different in the third), these reduce to five independent constants (see also *Thomsen parameters*). **Isotropic media** (where properties are the same measured in any direction) have only two independent elastic constants. The stress-strain properties of isotropic materials that obey Hooke’s law are specified by **elastic moduli** (Figure E-6).