Repeating a Previous Marine Seismic Survey with a Subsequent Survey that Employs a Different Number of Sources

A method of manufacturing a geophysical data product during the performance of a marine seismic 4D monitor survey that repeats a previous survey, wherein the previous survey employed a total of two sources, the method comprising:

• towing at least four sources asymmetrically relative to sail lines of the previous survey or to a crossline midpoint of the two sources employed in the previous survey;
• activating the four sources in a manner that repeats shot points produced during the previous survey and also produces additional shot points relative to the shot points produced during the previous survey;
• and
• recording, in a tangible non-transitory computer readable medium, signals generated by seismic sensors responsive to activating the four sources.

A method of performing a marine seismic 4D monitor survey that repeats a previous survey, comprising:

• towing a number of sources during the 4D monitor survey that is greater than a number of sources that were used to perform the previous survey, such that the monitor survey employs additional sources relative to the number of sources that were used to perform the previous survey;
• and
• activating the additional sources during the 4D monitor survey to produce additional shot points relative to shot points that were produced during the previous survey;
• wherein crossline outermost sources that were used to perform the previous survey define a previous survey crossline source spread;
• and
• wherein some of the additional shot points are produced at crossline positions outside the previous survey crossline source spread and others of the additional shot points are produced at crossline positions inside the previous survey crossline source spread.

A method of performing a marine seismic 4D monitor survey that repeats a previous survey, wherein at least first and second shot points were produced by one source during a single sail pass of the previous survey, the method comprising:

• towing three or more 4D monitor sources during the 4D monitor survey such that each 4D monitor source occupies a distinct crossline position;
• activating a first subset of the 4D monitor sources to repeat the first shot point;
• and
• activating a second subset of the 4D monitor sources to repeat the second shot point;
• wherein the first and second subsets are not identical.