Acoustic process and apparatus for logging by means of quadrupole shear wave

In logging the earth formation (30) surrounding a well (28), a quadrupole shear wave is transmitted, with the use of a quadrupole shear wave source(S) in a logging sonde (20), through the earth along the well. The presence of the shear wave successively at two points spaced iongitudinally along the well from each other is determined, using detectors (D1, D2). The time interval between the presence of the shear wave at the two points is measured by a time interval unit (40) for determining the velocity of the shear wave through the earth. …<??>In a modification, the time interval between transmitting the shear wave and detecting it at a single point spaced longitudinally from the transmission point is measured. …<IMAGE>…