Method for acoustic imaging of the earth's subsurface using non-linear signal generation and detection

A method for seismic surveying, comprising:

• disposing a plurality of seismic sensors in a selected pattern above an area of the Earth's subsurface to be evaluated;
• repeatedly actuating a seismic energy source proximate the seismic sensors, wherein a signal used to actuate the source comprises a linear chirp having a starting frequency and an ending frequency selected such that a signal resulting from non linear properties of subsurface formations has a frequency spectrum that does not overlap a frequency range of the linear chirp;
• recording signals generated by the seismic sensors indexed in time with respect to each actuation of the seismic energy source;
• and
• in a computer processing the recorded signals to generate an image corresponding to at least one point in the subsurface, the processing including stacking recordings from each sensor for a plurality of actuations of the source, cross correlating the stacked signals with an expected signal generated by non linearities in the subsurface and beam steering a response of the seismic sensors such that the at least one point is equivalent to a focal point of a response of the plurality of sensors.