Patent ID: 7751979

Claim:
A method of determining in-situ a relation between the seismic velocity and the state of stress in an underground formation located under a surface subjected to time-changing surface loading conditions, which method comprises the steps of (a) selecting a relation between the seismic velocity and the state of stress, which relation contains at least one unknown parameter; (b) placing a seismic source at surface or in a borehole penetrating the underground formation, and a seismic receiver at a distance from the seismic source at surface or in a second borehole; (c) determining at two different times the seismic velocity of the formation along a path from the seismic source to the seismic receiver; (d) converting the difference in surface loading conditions at the two times in a difference in states of stress in the underground formation; and (e) calculating the unknown parameter(s) that determine(s) the relation from the seismic velocities and the states of stress to obtain the relation between the seismic velocity and the state of stress in the underground formation.