Patent ID: 8498176

Claim:
A method of seismic exploration comprising the steps of: a) generating a seismic event; b) applying the seismic event to an earth's surface; c) detecting a response to the seismic event, using an interferometer, in which there is a relative motion between the earth's surface and the interferometer, the detected response including P-waves and S-waves in the earth's surface; and d) analyzing the detected response; wherein: the detecting step comprises the step of monitoring and recording the response to the seismic event in the form of movements of particles at the earth's surface, from a position spaced from the earth's surface, the detecting step being carried out over a response period, the response period being a predetermined period of time after the seismic event; the analyzing step comprises the step of analyzing the movements of particles at the earth's surface in the recorded response to the seismic event during the response period; the relative motion having a total velocity V 0 which includes a transversal or traversing component Vt and a longitudinal component V 1 ; and using the interferometer in step (c) of detecting a response to the seismic event includes the steps of: i) directing an object beam of coherent light to a measurement position at the earth's surface, there being relative motion between the surface and the measurement position; ii) arranging an array of detectors on the interferometer in a transversal detection line extending generally in the transversal direction, the detectors being arranged to detect light rays with different angular directions, representing different sensitivity directions; iii) producing a reference beam of coherent light which is at least partly coherent with the object beam; iv) combining the reference beam with the reflected object beam from the surface to produce a cross interference in a speckle pattern providing information about the relative motion between the surface and the interferometer; v) detecting the speckle pattern and a cross interference pattern with the detectors; vi) determining which detector in the array has zero or minimum sensitivity to the total velocity V 0 of the motion, thereby identifying the detector with a sensitivity direction line that is normal to V 0 ; vii) monitoring the temporal change in which of the detectors has zero or minimum sensitivity, thereby ascertaining the change in direction of V 0 over time, brought about by changes in V 1 ; and viii) determining temporal changes in V 1 .