SIGNAL ENHANCEMENT WITH AN ARRAY OF VERTICAL AND HORIZONTAL SEISMOMETERS

Abstract : Previous theoretical studies have indicated that arrays consisting of rings of radially oriented horizontal seismometers concentric with a central vertical seismometer are useful for the extraction of P-wave signals from Rayleigh-wave noise. To test this hypothesis, data were recorded at WMO from an experimental array having two horizontal rings and a central vertical seismometer. This report presents the results of processing the data. The two multichannel processors designed were a conventional Wiener infinite-velocity signal-extraction filter and an adaptive prediction-error filter. The Wiener processor, which was the better of the two, yielded about 4-db noise suppression over the 0.0- to 3.0-Hz frequency range. Both processors showed some signal distortion. Below 1.0 Hz, this poor performance is not surprising since, in this range, WMO is known to have a high level of P-wave noise which cannot be suppressed effectively by this type of array. At higher frequencies, however, much greater SNR improvement is to be expected. Examination of the recordings shows a great deal of variability along the individual horizontal-seismometer outputs and from output to output. This, coupled with the poor performance of the processors, suggests that the records contain a high level of nonseismic noise.