Linking Seismic Measurements to the International System of Units

The current state of the art in the calibration of seismometers is given by internal calibration procedures which give only incomplete information about a seismometer’s response and are based on transfer functions supplied by manufacturers. Calibrations traceable to the International System of Units (SI) provide an independent and comprehensible characterization of seismometers. These calibrations take part in a laboratory using an electrodynamic shaker or shake table. To overcome the issue that seismometers placed in seismic stations are not supposed to be moved to a calibration laboratory, novel on-site calibration methods incorporating a reference seismometer were developed. Such a reference is placed near the sensor to be calibrated, and the transfer function of the seismometer under test can be derived based on the output of both sensors.