Seismology is the study of acoustic waves in the earth. Earthquake seismology uses naturally occurring sound sources (earthquakes) to determine structure within the earth. Controlled source seismology uses man-made sound sources to study the earth. Earthquake seismology is geared primarily to structure within the earth's deep interior, while controlled source seismology is limited mainly to the crust and upper mantle, though the sound waves from nuclear explosions can travel through the deeper interior.
Reflection seismology is a subset of controlled source seismology. It is the primary method the oil industry uses to find mineral resources. Processing reflection seismic data is highly computer intensive. Approximately 30% of the world's entire CPU processing time is spent on reflection data processing alone! The amount of data collected can also be very large, typically running into the hundred's of Mbytes to ten's of Gbytes. (An experiment that I participated in conducted offshore Alaska collected about 400 Gbytes of data.)
Reflection seismology uses man-made sources to create sound waves. The size of sources can range from sledge hammers striking metal plates to large, several thousand pound chemical explosions. Sources in the water are typically airguns , large, metal canisters which fill up with compressed air that is suddenly released like the popping of a balloon. Environmentally sensitive Vibrator trucks can shake the ground very powerfully to produce sound waves.
The sound waves travel through the earth and reflect off boundaries between rock layers having different acoustic properties. The reflections are digitally recorded by a nominally linear array of small instruments called geophones. The data is processed to account for loss of signal with increasing distance, noise, geometrical factors, and other things. The final product is a seismic cross section . This one shows some folds lying under horizontal rock layers.
