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Maximum entropy spectral analysis of free oscillations of the earth : the 1964 Alaska event Davies, John Charles

Abstract

The DCLA gravimeter recording obtained after the 1964 Alaska earthquake, has been subjected to various, recently developed data processing techniques. In particular, the maximum entropy method (MEM) of spectral estimation and filter design was utilised. Prediction filters were used to extend the original tidal gravimeter recording, so as to avoid information loss caused by tapering the record prior to filtering. Time adaptive prediction error filters were then used to locate noise bursts, or 'glitches', which are present in the filtered record. The record was then deglitched using two methods, one a predictive approach, and the other involving a division of the record by a weighted envelope function. Power spectra using the classical periodogram approach, as well as MEM, were calculated for the filtered records, both before and after deglitching. This analysis resulted in new values for the splitting parameter 'β', and the centre frequency, for various free oscillation modes. A dramatic increase in the signal to noise ratio was also observed after the filtered records were deglitched. The presence of core mode oscillations was also investigated, but no evidence for these undertones was found. Instead, numerous peaks attributed to either instrument non-linearities, or barometric pressure effects, were found in the frequency range 0.12 to 1.20 cycles per hour.

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