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What can we consider a low frequency and what a high frequency?
The preceding little study of diffracted waves suggests
that we have the low-frequency case as soon as the diffracted spherical
wave and the transmitted plane wave interfere constructively.
In terms of distances, this condition can be written as
| |
(5) |

where is the wavelength of the waves, and *d*_{s} and
*d*_{p} are the distances traveled by the spherical and planar
waves, respectively, during a time *t*. The expression of *d*_{s}
is given by equation (4), and the distance *d*_{p} is simply

Then the condition (5) becomes
| |
(7) |

Finally, substituting into the latter equation,
we obtain the following low-frequency condition:
| |
(8) |

** Next:** Biot's sigmoid velocity versus
** Up:** P-VELOCITIES FOR DIFFERENT FREQUENCIES
** Previous:** Diffracted waves
Stanford Exploration Project

11/17/1997