Hi Petra. My you ask some very interesting questions. The answers are not easy, but here is one.
The people that the oil industries are using are seismologists. Seismology is the branch of geophysics that exploits the way that shock waves traveling through the earth are affected by different types of rock. The shock waves travel at different speeds in different types of rock, and are also affected by the density of the rock.
The boundaries between rocks with different properties reflect and refract shock waves. By recording shock waves received at the surface of the earth, from both earthquakes and man made "seismic sources", seismologists can determine the structure of the interior of the earth. Seismic recordings from man-made sources are used extensively for oil and gas exploration, after a great deal of computer enhancement and processing. Modern seismic methods are sensitive enough to deduce the presence of porosity in the rock at depths of several kilometres, or tell the seismic interpreter whether the sediments were deposited in the shallow waters of a river delta, or in deep water far from shore. Recordings of earthquake signals are used to deduce large scale structure of the entire earth, including its core.
In fundamental research, Canadian geophysicists are involved with an integrated national project called LITHOPROBE. Its goal is to increase the understanding of the crustal makeup of this country. The results of LITHOPROBE are at the forefront of world science. LITHOPROBE activities are helping to figure out the sinking (subduction) of slabs of the former Pacific seafloor beneath western Canada. LITHOPROBE results also show the relationship of the lower crust to the underlying parts of the earth. Such a massive project helps environmental geology in the assessment of earthquake and volcanic threats in the west. LITHOPROBE also provides data important in assessing the mineral potential of southern British Columbia, and to petroleum and natural gas exploration in Alberta.
Similar LITHOPROBE ventures have resulted in the discovery of the world's deepest rift in the Lake Superior region. Results of LITHOPROBE experiments are currently being applied to exploring the mineral belts of Ontario and Quebec. In the Maritimes, LITHOPROBE transects help to outline earth history events associated with the opening of a proto-Atlantic sea (the Iapetus Sea) and of the present Atlantic Ocean. The deep seismic results also help determine potential petroleum basins in the region. Hope this has helped. Take Care…Don in creepy town.