An accelerometer is a sensor that measures acceleration — the rate of change of velocity — typically by detecting the displacement of a proof mass relative to its frame. It is the most widely used sensor in earthquake engineering, structural health monitoring, and vibration analysis.
An accelerometer is a sensor that measures acceleration, typically through the displacement of a proof mass mounted on a spring and damper inside a housing attached to the structure. When the structure accelerates, the proof mass lags behind, and the relative displacement between the mass and the housing — measured capacitively, piezoelectrically, piezoresistively, or optically — is proportional to the acceleration. Modern accelerometers are available in a wide range of types, including MEMS accelerometers (small, low-cost, widely used in consumer electronics and increasingly in SHM), piezoelectric accelerometers (high sensitivity, wide frequency range, the standard for seismic and vibration applications), force-balance accelerometers (high precision, low noise, used for strong-motion recording), and fiber optic accelerometers (immune to electromagnetic interference, suitable for harsh environments).
Accelerometers are the primary sensor in earthquake engineering and structural health monitoring. In strong-motion seismology, accelerometers record the ground acceleration at free-field stations, providing the raw data for GMPE development, response spectra, and seismic hazard analysis. In structural monitoring, accelerometers are deployed throughout a building or bridge to record the response to earthquakes, ambient vibration, and operational loads — enabling modal identification, damage detection, and response history analysis. Modern strong-motion networks — such as those operated by the USGS, PEER, and national networks in Japan, Taiwan, and Iran — rely on thousands of accelerometers to produce the ground motion records used in research and design. In structural health monitoring, MEMS accelerometers are increasingly used because of their low cost, small size, and ease of deployment, enabling dense sensor networks on structures that would be impractical with traditional sensors.
Accelerometer selection and deployment involve several key considerations. Sensitivity and range must be matched to the expected motion — strong-motion accelerometers need a wide dynamic range to capture both small ambient vibrations and large earthquake motions without saturating. Frequency response must cover the frequency range of interest — for civil structures, typically 0.1 to 50 Hz. Noise floor determines the smallest motion that can be reliably measured. Mounting must ensure good mechanical coupling to the structure — poor mounting can introduce resonances and distort the measurement. Sensor placement determines which modes are observable and how well damage can be localized; optimal sensor placement is an active research area. Calibration must be performed periodically to ensure accuracy. Data acquisition — sampling rate, resolution, synchronization — must be matched to the application. In Iran, accelerometers are used in the national strong-motion network, in structural monitoring projects on bridges and critical buildings, and increasingly in low-cost SHM deployments using MEMS sensors. The integration of accelerometers with real-time data transmission and automated analysis is an active area of development, aiming toward rapid post-earthquake assessment and earthquake early warning.