For drama and fund raising, the enviros dub them "sonic cannons".
A new promising technique, "marine vibroseis" is showing promise, in shallower waters initially. Land vibroseis has long been successfully used. It is highly directional and limited to a low, specific frequency. IOW, it emits much less 'noise' that can harm sea mammals. The current very expensive workaround is a set of solutions that essentially avoids sea mammals.
For a sense of proportion, a seismic survey of an area might cost $5 million and a well $50 million. But you don't know what you've got until you do a survey. As in the Carolinas, for general economic development reasons, seismic surveys are often a government backed, sponsored or even funded activity. Anything to please the enviros on seismics is money well spent.
Because the next President will be for oil exploration and he does not want to look like the fool he is, for curtailing oil exploration!