Calibration of the Wiechert seismographs relative to a reference seismometer

Abstract

The horizontal 1000 kg Wiechert seismograph has been calibrated on the basis of a comparison of its records to the ones that were obtained by the reference seismometer. The resulting magnification curve shows notable deviations from the theoretical one. Its most prominent feature is a sudden magnification increase observed for frequencies above 5 Hz, which is attributed to frame oscillations excited by the seismic waves. Also, the observed average response curve exhibits larger magnification for frequencies below the resonance frequency. The results indicate a non-linear behavior of the Wiechert instrument related to the degree of impulsiveness of the excitation.