A thumper for active seismology work
Seismology is the study of what is under the surface of the Earth by measuring vibrations on the Earth's surface. A person who does this is called a seismologist.
It is part of the science of geophysics, which studies the physics of the processes that formed the Earth and other planets.
Seismology is done by seismologists and geophysicists using devices to pick up the vibrations called geophones, hydrophones or seismometers.