On-site calibration of a broadband seismometer

Broadband seismometers are widely used in global seismic observation networks for geoscientific research and international nuclear test monitoring. To ensure the reliability of such seismometers without any downtime, on-site or in-situ calibration is required. To demonstrate a traceable calibration of such seismometers, a comparison calibration at an underground observation site was conducted. The reference seismometer was calibrated using a primary vibration calibration system in the laboratory. Consequently, the in-situ complex sensitivity at the midband frequency (0.25 Hz) was determined using the microseism peak, with a measurement duration of around an hour. We find that traceable calibration at the midband frequency is an efficient means of ensuring the traceability of the seismometer during operation, particularly when coupled with electrical frequency response measurements.