Geophones are small, vibration-sensing instruments that are used to measure movement or vibration of the earth, machines, mines, and other applications. Frequency range and application are the most important factors to consider. Short-period geophones can measure frequencies around 1 Hz and are designed to record localized seismic events such as earthquakes. Long-period geophones can measure frequencies around 4.5 Hz and are suitable for oil exploration and teleseismic events. Both types of products work like gravity meters in that the active geophone element consists of a cylinder which hangs from a spring. The cylinder is wrapped in a coil of copper wire and surrounded by a magnet or magnetic housing that is fixed to the earth. The earth’s movement causes the magnet to move around the mass and produce an electrical voltage which is transmitted along the wire, amplified and then recorded. The recorded voltage is proportional to the velocity at which the ground is moving.

Geophones consist of a cylinder, wire coil, magnet, leaf spring, and two-part housing. Wires that extend from the sides of a plastic external case transmit variations in voltage to the recording system. The metallic internal case is magnetized. Some geophones have a long spike that can be used to press the device into the ground. Geophones without spikes are designed for hard surfaces. Performance specifications for geophones include resonant frequency, proof mass (g), peak sensitivity (V/g), and coil resistance (ohms). Noise, linearity, and dynamic range are additional considerations. As a rule, the sensitivity of a geophone as a function of frequency can be altered by feeding back the conventional output. This does not improve the resolution, but amplifies low-frequency signals. Measuring proof-mass position provides a way to improve resolution.

Geophones are small, vibration-sensing instruments that are used to measure movement or vibration of the earth, machines, mines, and other applications. Frequency range and application are the most important factors to consider. Short-period geophones can measure frequencies around 1 Hz and are designed to record localized seismic events such as earthquakes. Long-period geophones can measure frequencies around 4.5 Hz and are suitable for oil exploration and teleseismic events. Both types of products work like gravity meters in that the active geophone element consists of a cylinder which hangs from a spring. The cylinder is wrapped in a coil of copper wire and surrounded by a magnet or magnetic housing that is fixed to the earth. The earth’s movement causes the magnet to move around the mass and produce an electrical voltage which is transmitted along the wire, amplified and then recorded. The recorded voltage is proportional to the velocity at which the ground is moving.

Geophones consist of a cylinder, wire coil, magnet, leaf spring, and two-part housing. Wires that extend from the sides of a plastic external case transmit variations in voltage to the recording system. The metallic internal case is magnetized. Some geophones have a long spike that can be used to press the device into the ground. Geophones without spikes are designed for hard surfaces. Performance specifications for geophones include resonant frequency, proof mass (g), peak sensitivity (V/g), and coil resistance (ohms). Noise, linearity, and dynamic range are additional considerations. As a rule, the sensitivity of a geophone as a function of frequency can be altered by feeding back the conventional output. This does not improve the resolution, but amplifies low-frequency signals. Measuring proof-mass position provides a way to improve resolution.

Petroleum companies often use geophones to reduce the number of drilling pads required for site exploration and development. Seismic surveys can map the subsurface by using vibrator trucks or low-level explosives to generate underground shock waves that are recorded by geophones. Placing geophones along intersecting grid lines enables computers to produce three-dimensional (3D) models of subsurface rock formations that can identify areas that contain hydrocarbons.