geophone

A geophone is a device that converts ground motion into an electrical signal, primarily used to record seismic vibrations. In a typical moving-coil geophone, a mass is attached to springs inside a case and coupled to a coil in a magnetic circuit. When the ground moves, inertia causes relative motion between the mass and the case; this relative motion induces a voltage in the coil proportional to the ground velocity. Some designs use piezoelectric elements and report displacement rather than velocity. Geophones are usually single-axis instruments, but tri-axial versions are available, and can be deployed vertically and horizontally to capture full 3D motion. The sensor’s natural frequency, set by mass and spring stiffness, determines its frequency response: higher natural frequency yields better high-frequency response but reduced sensitivity at low frequencies.

Geophones are widely used in seismology, earthquake monitoring, and subsurface exploration. In geophysical surveys, dense arrays of geophones record reflected or refracted seismic waves generated by a controlled source, enabling imaging of subsurface structures. In construction and mining, they monitor vibrations from blasting or equipment. Geophones typically require a preamplifier and data acquisition system; low-noise amplification and proper coupling to the ground improve signal quality. Burial or direct grounding often improves coupling and reduces wind and thermal noise.

Compared with broadband seismometers, geophones offer ruggedness, relatively low cost, and simplicity, but have limited low-frequency response and a smaller dynamic range. Calibration and proper orientation are important for accurate measurements, and many installations employ multiple sensors to capture multi-directional ground motion.