Geophones are ground displacement sensors/transducers used for seismic energy measurements. Geophone is also called as seismic geophones or Seismometers. The geophone is a passive device requiring no additional power which converts seismic energy (ground displacement or vibrations) into an electrical signal producing an output voltage which is proportional to the geophone velocity.

Working Principle of Geophone

Geophones have a coil hanging from a spring in the center of some magnets. When the case is moved up and down the mass tends to stay put and induces small currents into the coil as it moves through the magnetic field. It measures velocity of motion. The response of a coil/magnet geophone is proportional to ground velocity, while microelectromechanical systems devices usually respond proportional to acceleration. The geophone’s output current is used to move a pen over paper or gets recorded into a computer for analysis with Richter scale display. Microelectromechanical systems have a much higher noise level (50 dB velocity higher) than geophones and can only be used in strong motion or active seismic applications.

Different Types of Geophones

Many different types of geophones are being manufactured nowadays, the mechanical/vibrational geophones, solidstate MEMS geophone chips, and self-powered wireless geophones that can measure and transmit the seismic data wirelessly to the recording station.

Applications of Geophones

They are designed for measurement of earthquakes, machine vibrations, oil exploration, mining, etc. Wireless geophones are also used is in the application of Remote Ground Sensors (RGS) incorporated in Unattended Ground Sensor (UGS) Systems. The majority of geophones are used in reflection seismology to record the energy waves reflected by the subsurface geology.

The sensitivity of passive geophones is typically 30 Volts/(meter/second), so they are in general not a replacement for broadband seismometers.

Some applications of geophones are interested only in very local events. A notable example is in the application of Remote Ground Sensors (RGS) incorporated in Unattended Ground Sensor (UGS) Systems. In such an application there is an area of interest which when penetrated a system operator is to be informed, perhaps by an alert which could be accompanied by supporting photographic data.