The Güralp Stratis: A Commercial Six-Degree-of-Freedom Seismometer for Ground Motion and Structural Monitoring

Traditional research-grade three-component seismic sensors are inherently sensitive to both translational ground motion and rotational (tilt) motion, particularly on the horizontal components. The outputs of traditional seismometers represent a sum of rotation and displacement information. As a result, recorded signals represent a superposition of displacement and rotation, even though most processing and interpretation workflows assume purely translational motion. This limitation becomes increasingly important for applications involving near-field ground motion, ground-structure interaction, and structural response monitoring, where rotational effects can significantly influence observed building and infrastructure dynamics. Recent advances in sensor technology are now allowing accurate and precise discrimination between translational and rotational motion. Stratis is the world’s first integrated seismic sensor to provide simultaneous, co-located measurements of all six degrees of freedom, delivering concurrent velocity (m/s) and rotational velocity (rad/s) outputs in the Z, N, and E directions. By measuring all six degrees of freedom at a single point, Stratis avoids the spatial differencing and approximation errors associated with multi-instrument rotational estimates. The availability of co-located rotational measurements enables correction for tilt-induced contamination in translational records, supporting the derivation of rotation-corrected displacement signals and improving the fidelity of ground motion and structural response observations. By integrating rotational and translational sensing into a single compact instrument, the installation process is also greatly simplified, thereby enabling wider access to rotational seismic data. This supports interdisciplinary applications spanning seismology, structural engineering, and seismic risk mitigation, including post-event damage assessment, long-term monitoring of structural health, and improved characterization of earthquake ground motion relevant to robust infrastructure design.