A method for seismic surveying is disclosed which includes towing a first seismic
energy source and at least one seismic sensor system. A second seismic energy source
is towed at a selected distance from the first source. The first seismic energy
source and the second seismic energy source are actuated in a plurality of firing
sequences. Each of the firing sequences includes firing of the first source, waiting
a selected time firing the second source and recording signals generated by the
seismic sensor system. The selected time between firing the first source and the
second source is varied between successive ones of the firing sequences. The firing
times of the first and second source are indexed so as to enable separate identification
of seismic events originating from the first source and seismic events originating
from the second source in detected seismic signals.
