Seismic testing utilizes sound waves and sensors to create a three-dimensional map of an underground area to determine what kinds of mineral resources are available. Vibrations are created using special trucks or detonated explosives. Sensors receive the vibrations and take measurements. This data is fed into complex computer programs that create maps of the area, and geologists interpret the maps to discover what minerals lie beneath the surface.
Probes called geophones are placed several hundred feet apart to sense data. Large drills bore dozens of feet into the Earth for the charge placement. Explosive charges are dropped into the drilled holes. When the explosives detonate, the geophones sense the soundwaves coming through the ground.
Another method to produce vibrations utilizes special trucks called Vibroseis. These trucks have huge metal plates underneath them that drop down onto the ground. The heavy plates have the full weight of the truck on top of them. The plate vibrates at a specific frequency to create seismic waves.
Computers interpret the data gathered by the sensors. Originally, two-dimensional maps were created using seismic testing techniques. When more sophisticated computers were developed in the 1980s, three-dimensional models became standard. Seismic testing is done both on the Earth's surface and underwater, mainly for oil and gas exploration.