  In order to compare the ratios between the amplitudes of P and S acoustic
waves drawn from various boreholes, we have defined a specific wave parameter
called magnitude : for each shot, we have added the maximum positive amplitude
values and the absolute values of the minimum negative amplitudes of a given
wave recorded at different depths. In compact formations, the difference
between the logarithms of the magnitudes of S and P waves provides a value that
appears to be characteristic of the state of stress of the domain where a
borehole is drilled. Accidents between those formations, such as fractures or
sedimentary joints can be determined, and breakouts well distinguished.
