The Distortion of Pulse-like Earthquake Signals by Seismographs

This is the authors' abstract. We don't add key points for this paper.

A numerical method for calculating the seismogram of any seismograph for an arbitrary continuous ground disturbance is used to investigate the effect of instruments with various physical constants on both theoretical and actual impulsive signals. This calculation solves the equations of motion of the pendulum-galvanometer system by a fourth-order Runge-Kutta process. Variation of instrumental constants produces conspicuously different seismograms, in several cases of practical interest. In order to resolve the apparent discrepancy between the observations of Satô, and those of Benioff and Press for the group velocity of long period Love waves, certain computed seismograms of the long period Love wave arrival, G1, from the New Guinea shock of 1938 February 1, were compared with the linear strain recording of this signal. The results of this study confirm the observations of Satô, that the group velocity of Love waves is essentially flat in the long period range to several hundred seconds. The distortion introduced by instruments whose magnification changes rapidly with period is great enough to mask any small dispersion that might be associated with these pulse-like signals.