Acoustic logging apparatus and method

An apparatus for determining shear wave velocity and orientation in an earth formation, comprising:

• at most one source capable of generating acoustic signals within a borehole;
• at least four source-independent pressure transducer receivers capable of receiving acoustic signals from the formation;
• and
• a processing device capable of processing said acoustic signals, wherein said processing device interpolates the pressure field between two adjacent receivers.

A apparatus for determining shear wave velocity and orientation in an earth formation, comprising:

• a single dipole source capable of generating acoustic signals within a borehole;
• at least four receivers capable of receiving acoustic signals from the earth formation and configured to measure pressure fields;
• a processing device capable of processing said acoustic signals;
• wherein said processing device interpolates the pressure field between any two adjacent receivers and performs cross-component decomposition on the pressure field to determine shear wave orientation and velocity.

A method for determining anisotropy in an earth formation, comprising:

• measuring pressure fields at four circumferentially spaced receivers;
• interpolating the pressure fields between any two adjacent receivers;
• and
• subtracting pressure fields 180° apart to detect shear waves.