NUMERICAL MODELING OF THE OBSERVED WIECHERT SEISMOGRAPH MAGNIFICATION

The paper presents results of experiments designed to measure the actu al dynamic magnification of the Wiechert 1000 kg horizontal seismomete r 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 t he magnification of the Wiechert seismometer is influenced by the inte raction of its mass and frame, especially for high frequencies. This i nteraction has been modeled by considering a system of two coupled pen dulums, yielding a theoretical dynamic magnification curve which exhib its main features of the observed magnification. The discrepancy betwe en the nominal and the actual response of the Wiechert seismograph may lead to errors in studies involving spectral analyses of recorded sei smograms, and to overestimation of local earthquake magnitudes.