Geophones are small, cheap instruments instrument for measuring
ground motion. There are many different varieties for different
applications. They are designed for earthquakes, machine
vibrations, oil exploration, mining, etc...
Additional information available at
"http://www.tenrats.org/whatis"
A geophone is a device that converts ground movement (velocity) into voltage, which may be recorded at a recording station. The deviation of this measured voltage from the base line is called the seismic response and is analyzed for structure of the earth.
