Seismometre

A seismometre, also spelled seismometer in American usage, is an instrument that records ground motion produced by earthquakes, volcanic activity, explosions, and other geophysical processes. It typically records the relative motion between a suspended mass and the surrounding frame, producing a signal called a seismogram that reflects displacement, velocity, or acceleration of the ground.

Principle and components

Most modern seismometres employ an inertial sensor in which a mass is connected to a spring or pendulum. When the ground moves, the frame is accelerated while the mass tends to remain in place, creating a relative motion that is converted into an electrical signal by a transducer (capacitive, inductive, optical, or gantry-based). The instrument is usually housed in a stable enclosure and synchronized with precise time standards, often via GPS, to allow data from many stations to be combined.

Types and ranges

There are several types designed for different frequency ranges and amplitudes. Short-period seismometers are sensitive to higher frequencies and are commonly used near the source of earthquakes. Broadband seismometers aim to record a wide range of frequencies to study both local and distant events. Strong-motion seismometers are built to withstand large ground motions near large earthquakes. Most installations measure three components: vertical, north-south, and east-west, though some networks use two horizontal and one vertical channel or other configurations.

Applications

Seismometres are fundamental to earthquake localization, magnitude estimation, and structural investigations of the Earth’s interior. They underpin seismic networks, data centers, and early-warning systems, enabling rapid alerts, hazard assessment, and scientific analysis of seismic waves and ambient ground noise.