Method of processing seismic data acquired by reflection seismic survey

1 . A method of processing seismic data by a reflection seismic survey using a seismic source that outputs an acoustic wave into water and a receiver that receives the acoustic wave, the method including:

calculating a first pseudo-water-surface reflection wave by virtually propagating a direct wave represented in the seismic data in a progressing direction of a tip axis by a time in which the acoustic wave propagates in the water at a distance twice a depth of the seismic source, and further correcting an amplitude of the direct wave so that the amplitude is approximated to an amplitude of a water-surface reflection wave of the acoustic wave represented in the seismic data; and

subtracting a component corresponding to the first pseudo-water-surface reflection wave from the seismic data;

wherein

the direct wave is an acoustic wave output from the seismic source and reflected on a reflection surface without going through reflection on the water surface;

the first water-surface reflection wave is an acoustic wave which is output from the seismic source and reflected on a water surface and further on the reflection surface, thereby being delayed by a time corresponding to a distance twice the depth of the seismic source.

2 . The method of processing the seismic data according to claim 1 , further including:

calculating a first pseudo direct wave by: virtually propagating the first water-surface reflection wave in a direction opposite to the progressing direction of the time axis by the time in which the acoustic wave propagates in the water at the distance twice the depth of the seismic source, and inversing a phase thereof; and

adding data showing the first pseudo direct wave to the seismic data in which components corresponding to the first pseudo-water-surface reflection wave are subtracted.

3 . The method of processing the seismic data according to claim 1 , further including:

calculating a second pseudo-water-surface reflection wave by virtually propagating the direct wave of the acoustic wave represented in the seismic data in the progressing direction of the time axis by a time in which the acoustic wave propagates in the water at a distance twice a depth of the receiver, and correcting an amplitude of the propagated direct wave so that the amplitude is approximated to an amplitude of a second water-surface reflection wave of the acoustic wave represented in the seismic data;

calculating a third pseudo-water-surface reflection wave by virtually propagating the direct wave in the progressing direction of the time axis by the time in which the acoustic wave propagates in the water at the distance twice the depth of the seismic source and twice the depth of the receiver, and correcting an amplitude of the propagated direct wave so that the amplitude is approximated to an amplitude of a third water-surface reflection wave of the acoustic wave represented in the seismic data; and

subtracting components of the second and the third pseudo-water-surface reflection waves from the seismic data;

wherein

the second water-surface reflection wave is an acoustic wave which is output from the seismic source, reflected on the reflection surface, and further reflected on the water surface, thereby being delayed by a time corresponding to a distance twice the depth of the receiver, and

the third water-surface reflection wave is an acoustic wave which is output from the seismic source, reflected on the water surface, reflected on the reflection surface, and further reflected on the water surface, thereby being delayed by the time corresponding to the distance twice the depth of the seismic source and a time corresponding to the distance twice the depth of the receiver.

4 . The method of processing the seismic data according to claim 3 , further including:

calculating a first pseudo direct wave by: virtually propagating the first water-surface reflection wave in a direction opposite to the progressing direction of the time axis by the time in which the acoustic wave propagates in the water at the distance twice the depth of the seismic source in which the acoustic wave propagates in the water at the distance twice the depth of the seismic source, and inversing a phase thereof;

calculating a second pseudo direct wave by: virtually propagating the second water-surface reflection wave in a direction opposite to the progressing direction of the time axis by the time in which the acoustic wave propagates in the water at the distance twice the depth of the receiver, and reversing a phase thereof;

calculating a third pseudo direct wave by: virtually propagating the first water-surface reflection wave in a direction opposite to the progressing direction of the time axis by the time in which the acoustic wave propagates in the water at the distance twice the depth of the seismic source and the time in which the acoustic wave propagates in the water at the distance twice the depth of the receiver, and inversing a phase thereof; and

adding data representing the first, the second, and the third pseudo direct waves to the seismic data in which components corresponding to the first, the second, and the third pseudo-water-surface reflection wave are subtracted.