EARTHQUAKES AND THE SPECTRUM OF THE BRUSSELS SUPERCONDUCTING GRAVIMETER DATA FOR 1982-1986

Spectral analysis of the Brussels Superconducting Gravimeter data from 1982 to 1986 by earlier workers revealed a decaying spectral peak at 13.89 h following the December 30, 1983, Hindu Kush earthquake. Similar associations were presented for several other large earthquakes. The presence of the observed 13.89-h spectral peak was ascribed to possible excitation of inertial waves in the fluid outer core of the Earth. In this paper, the same data set is analysed with a moving window spectral method that shows the variation of the power in this and other spectral bands. Also, confidence intervals for the spectral estimates are computed. No unambiguous relation with the earthquake sequence used previously is found, and no statistically significant non-tidal spectral peak is found in the band between 12 and 24 h. However, the moving window spectral method applied to the 4.8- and 8-h spectral bands shows a closer association with the earthquake sequence. Again, although confidence interval calculations show some statistically significant spectral features in these bands, there is evidence that at least some of these features are generated by non-linear tidal interactions or possibly over-correction of the raw data for tidal signals. It is speculated that if indeed earthquake-induced, long-period core waves cause a detectable gravity signal, then the spectrum is perhaps richer in the short-period bands. © 1990.