Reflection seismology is a method used to image sequence boundaries in the subsurface. Those sequence boundaries are generated by a change in deposited material (e.g., sedimentary or magmatic rocks) or via geological events such as erosion, modifications in depositional conditions or tectonic movements. They are documented in modifications of the density and/or seismic velocities of the rocks. Seismic reflection experiments are carried out to study the structure of the subsurface and reconstruct geological or geophysical boundaries. Seismic waves are generated artificially (marine reflection seismology mainly uses airguns) they propagate through the subsurface, and are reflected and transmitted at geological/geophysical boundaries. Part of the reflected wave field moves back to the surface. There, both energy and traveltime of the waves are recorded with socalled geophones, in marine reflection seismology with hydrophones in a streamer. At geological/geophysical boundaries the seismic wave is further converted into other wave types.
The seismic waves are recorded by a number of geophones/hydrophones in order to 'stack' the data (add up the recordings) thus improving the signal-to-noise ratio of the data. This is called multichannel seismics.