MULTIPLE COHERENCE OF LONG PERIOD NOISE AT LASA
Seismic data lab. rept.
TELEDYNE INDUSTRIES INC ALEXANDRIA VA EARTH SCIENCES DIV
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Multiple coherence gives a quantitative measure versus frequency of how well a linear combination of n input channels can match the n 1 st channel in a seismic array. If the inputs can match the output exactly, then the multiple coherence is unity and only n channels are necessary to describe the noise field. This report shows multiple coherence versus frequency with 2 to 9 input channels for long period, vertical component noise fields at LASA. Over the 7 to 20 seconds period range the multiple coherence on the samples tested were greater than .65 showing that 65 or more of the noise at a center channel is predictable by other seismometer outputs in the array. This level of multiple coherence requires 8 to 9 input channels. Multiple coherence with fewer inputs ordinary coherence between pairs of channels are must lower. From the samples tested which all produce multiple coherences quite similar to each other, it is concluded that at least 9 input channels are necessary to adequately describe the long period noise at LASA.