An article in The Marietta Times (Marietta, Ohio) does an excellent job of describing the process of seismic mapping recently performed in the City of Marietta. Having a map of underground structures—how the rock formations and layers are arranged—is worth millions to drillers. So they hire companies to create maps.
Cables are laid along side roadways and a truck moves along “stopping at regular intervals to lower large vibrating metal disks from each truck onto the road surface.” The cables record seismic vibrations and create a 2-dimensional map of structures under the surface.
The initial 2-D mapping shows what’s happening directly beneath the road. If companies see areas that pique their interest, they then order a 3-D map, a more involved process. But they hardly ever (perhaps never) order 3-D maps for cities because drillers typically don’t want to deal with signing hundreds or thousands of individual landowners over a relatively small area. So the question is, why were seismic trucks doing 2-D mapping inside the city limits of Marietta if no drillers would ever want to drill there?