EVALUATION OF THE COUPLING CHARACTERISTICS OF BOTTOM SEISMOGRAPHS FROM MICROSHOCK TRACES

Abstract

This paper describes a method of analyzing the fine structure of seismic spectra recorded with bottom seismographs (BS). This technique can be used to evaluate the distortions of the signal spectrum introduced by the frequency characteristic of the junction between the sea bottom and the instrument, and thus to reveal the spectral properties of the signals, which contain information on the source and the medium in which the waves propagate. The experimental data indicate that in certain cases the coupling characteristic of a bottom seismograph evaluated from a correctly chosen microshock trace is in satisfactory agreement with the real frequency response of the sea bottom-seismograph junction. The coupling properties evaluated from different microshocks in the same recording are in good agreement. The results indicate that when comparing the data obtained with different bottom seismographs, the shapes of earthquake spectra and other signals can and should be analyzed with correction for the coupling characteristics of the relevant sites, computed from the Fourier transformations of the traces of suitable microshocks. At present this appears to be the only method of evaluating the effect of the coupling characteristics of bottom seismographs in situ in the deep ocean.