seismic

• Seismic surveys locate geological structures (boundaries). They can evaluate sand and gravel deposits, and define ancient landfill sites. 
• Seismic surveys can be land or sea based. 
• For a seismic survey and artificial source of sound waves is required, along with an array of detectors/geophones and mobile recording equipment. 
• Sound waves used to be generated with dynamite, currently thumper trucks and air guns at sea are used. 
• Only P waves are recorded from the generation of waves. 
• Seismic surveys require the velocity of rocks, velocity can vary due to water in pore spaces and pressure. Boreholes can provide info about velocities.