The schematic figure shows seismic energy being generated by four vibroseis trucks.
Some experiments use explosives as the energy source, while other experiments utilize earthquakes. The waves propagate through the earth and reflect or refract when reaching a transition between rocks with different physical properties. The waves are reflected or refracted (bent) back to the earth's surface where the energy is detected by geophones (marked by yellow flags) and recorded by a computer. A typical LITHOPROBE geophone array includes 240 geophone groups that extend 8 km ahead of the vibrators and 4 km behind. When vibrating every 100 m, this type of seismic reflection crew covers approximately 20 km per day. Measuring the time it takes the energy to follow the various paths allows the transitions to be mapped. Enough energy is generated by 4 vibrators to successfully map crustal structures to the base of the crust (approximately 30 to 50 km beneath continents).