Dictionary:Epsilon ε

1. Dielectric permittivity; see Maxwell’s equations.

2 The fractional change in the P-wave velocity:

$\varepsilon ={\frac {c_{11}-c_{33}}{2c_{33}}}={\frac {\alpha _{\perp }-\alpha _{\parallel }}{2\alpha _{\parallel }}}$

where c₁₁ and c₃₃ are transverse isotropy elastic constants. See Thomsen anisotropic parameters.