MULTIPLE COHERENCE OF SHORT 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 short period noise fields at LASA. Intersubarray noise from the center seismometers in the 500 foot holes at LASA shows low multiple coherence for all frequencies from 0.1 to 2.5 cps even with the closest subarrays represented. The intersubarray multiple coherence indicates that the expected noise reduction from a prediction error filter is about 1 db over the fitting interval and about 0 db outside the fitting interval. Intrasubarray noise has a high multiple coherence for frequencies of 1 cps and lower when some input channels are within half km of the output channel. When the inputs are at least 2 km away, the multiple coherence is less than 0.8 for all but microseismic frequencies.
- Seismic Detection and Detectors