Final answer:
Sub-surface surveys are conducted in archaeology to identify potential sites with cultural artifacts before excavation and in geology for locating oil and gas reserves using 3D seismic technology.
Step-by-step explanation:
A sub-surface survey is typically conducted prior to an archaeological excavation or part of geological research such as oil exploration. In archaeology, a sub-surface survey is used to detect and map underground features that suggest human activity, like the presence of cultural debris or artifacts. To do this, various technologies like drones and satellite imagery might be utilized to identify unusual topographical features from above that are not easily seen from ground level. Once potential sites are located, more invasive methods, including test pits and sampling, can be used to ascertain the significance of the findings.
In the field of geology, particularly in the oil and gas industry, sub-surface surveys play a critical role. For instance, 3D seismic surveys create a detailed image of the subsurface structures by acquiring seismic data along closely spaced lines, which are then processed and interpreted. This technology, used since 1967, helps in pinpointing the location of oil and gas reserves without the need for invasive drilling. The first 3D seismic survey was completed by Exxon in Texas, and modern surveys can have seismic traces spaced at intervals as small as 12.5 meters.
Regardless of the specific field, sub-surface surveys are conducted to better understand what lies beneath the surface before any excavation or drilling takes place, which can help in planning and mitigating potential impacts on the environment or cultural sites.