Title of Invention	SEISMIC EXPLORATION USING INTERFEROMETRIC
Abstract	A method and apparatus for carrying our seismic exploration which comprises generating a seismic event; applying the seismic event to the earth's surface; detecting a response to the event, using an interferometer, in which there is 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 analysing the detected response; and in which: the detecting step comprises 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; and the analysing step comprises analysing the movements of particles at the earth's surface in the recorded response to the seismic event during the response period; the said relative motion having a total velocity Vtot which includes a transversal or traversing component Vt and a longitudinal component VI; operation of the interferometer including: directing an object beam of coherent light to a measuring position at the earth's surface, whereby there is relative motion between the surface and the measurement position; arranging an array of detectors on the interferometer in a line extending generally in the transversal direction, the detectors being arranged to detect light rays with different angular directions, representing different sensitivity directions; producing a reference beam of coherent light which is at least partly coherent with the object beam; combining the reference beam with the reflected object beam from the surface to produce a cross interference in the speckle pattern providing information about the relative motion of the surface and the interferometer; detecting the speckle pattern and the cross interference pattern with the detectors; determining which detector in the array has zero or minimum sensitivity to the total velocity Vtot of the motion thereby identifying the detector with a sensitivity direction line that is normal to Vtot; monitoring the temporal change in which of the detectors has zero or minimum sensitivity, thereby ascertaining the change in direction of Vtot over time, brought about by changes in VI; and determining temporal changes in VI.

Title of Invention

SEISMIC EXPLORATION USING INTERFEROMETRIC

Abstract

A method and apparatus for carrying our seismic exploration which comprises generating a seismic event; applying the seismic event to the earth's surface; detecting a response to the event, using an interferometer, in which there is 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 analysing the detected response; and in which: the detecting step comprises 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; and the analysing step comprises analysing the movements of particles at the earth's surface in the recorded response to the seismic event during the response period; the said relative motion having a total velocity Vtot which includes a transversal or traversing component Vt and a longitudinal component VI; operation of the interferometer including: directing an object beam of coherent light to a measuring position at the earth's surface, whereby there is relative motion between the surface and the measurement position; arranging an array of detectors on the interferometer in a line extending generally in the transversal direction, the detectors being arranged to detect light rays with different angular directions, representing different sensitivity directions; producing a reference beam of coherent light which is at least partly coherent with the object beam; combining the reference beam with the reflected object beam from the surface to produce a cross interference in the speckle pattern providing information about the relative motion of the surface and the interferometer; detecting the speckle pattern and the cross interference pattern with the detectors; determining which detector in the array has zero or minimum sensitivity to the total velocity Vtot of the motion thereby identifying the detector with a sensitivity direction line that is normal to Vtot; monitoring the temporal change in which of the detectors has zero or minimum sensitivity, thereby ascertaining the change in direction of Vtot over time, brought about by changes in VI; and determining temporal changes in VI.

SEISMIC EXPLORATION USING INTERFEROMETRIC

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