Eq. 4 decomposes the wavefield into a near-field term decaying with *r*^{-2} and a far-field term decaying with *r*^{-1}:

In case of a harmonic time dependence we have

(7) |

and

(8) |

where is the wavelength. The far-field term thus dominates at radii greater than wavelengths. When the deformation is quasistatic (i.e. sufficiently slow), only the near-field term is relevant.

2001-09-21