Methods of employing vibrational energy in a borehole

A method of obtaining information indicative of the earth's structure adjacent a borehole that has a generally cylindrical wall that extends from the earth's surface, comprising:

• positioning an instrument housing in the borehole, the instrument housing having an internal cylindrical surface;
• positioning a mass having a rotational axis in said instrument housing, the mass having an external surface of dimension less than the instrument housing internal cylindrical surface;
• rotating said mass about its rotational axis in a selected direction in said instrument housing and causing said surface of said mass to contact said internal cylindrical surface to thereby cause said mass to backward whirl in the direction opposite to said direction of rotation of said mass, centrifugal force of the backward whirling mass serving to generate vibrational energy that is radiated into the earth as a seismic signal;
• positioning at least one geophone in acoustical contact with the earth at a location remote from said rotating mass for receiving seismic signals resulting from vibrational energy generated by said backward whirling mass;
• collecting data generated by said at least one geophone;
• and
• processing the collected data to provide information indicative of the earth's structure adjacent the borehole.