seismometer

A seismometer is an instrument that measures and records ground motions produced by earthquakes, explosions, and other sources of vibration. It converts ground displacement, velocity, or acceleration into electrical signals that can be stored, analyzed, and displayed. Modern seismometers feed data to digital recorders and are deployed in arrays across the globe to monitor seismic activity.

Principle and design: The principle is that a mass suspended on springs inside a housing tends to stay at rest while the ground moves. The relative motion between the frame and the mass is detected by sensors (electromagnetic, capacitive, or piezoelectric) and converted into electrical signals. Three-component devices record motion in vertical and two horizontal directions. Many instruments timestamp data with GPS for precise correlation.

Types and applications: Seismometers are categorized by frequency response and dynamic range. Short-period sensors capture higher frequencies for local earthquakes; long-period instruments record lower frequencies for distant events; broadband sensors cover a wide range; strong-motion sensors are designed for large earthquakes. They may be standalone units or part of three-component stations, often paired with accelerometers or velocity sensors. Applications include earthquake monitoring and location, magnitude estimation, tsunami and landslide warning, exploration geophysics, and volcano monitoring. Global networks use seismometer data to construct Earth models and to monitor compliance with nuclear test-ban treaties.

Networks and data: Major networks such as the Global Seismographic Network and regional arrays collect data from thousands of seismometers. The data are shared in standardized formats (SEED/MiniSEED) and interpreted to determine earthquake parameters, including epicenter, depth, and fault mechanism. Timekeeping is typically synchronized with GPS to ensure accurate timing across stations.