Numerical Modeling of the Observed Wiechert Seismograph Magnification

The paper presents results of experiments designed to measure the actual dynamic magnification of the Wiechert 1000 kg horizontal seismometer when excited by seismic waves. This is accomplished by comparing 51 digital records of seismic events recorded by the Wiechert and a well calibrated reference seismometer. The results obtained indicate that the magnification of the Wiechert seismometer is influenced by the interaction of its mass and frame, especially for high frequencies. This interaction has been modeled by considering a system of two coupled pendulums, yielding a theoretical dynamic magnification curve which exhibits main features of the observed magnification. The discrepancy between the nominal and the actual response of the Wiechert seismograph may lead to errors in studies involving spectral analyses of recorded seismograms, and to overestimation of local earthquake magnitudes.