LARGE-ARRAY SIGNAL AND NOISE ANALYSIS. SPACE AND TIME VARIABILITY OF THE SHORT-PERIOD LASA NOISE FIELD
Abstract
To study the time and space variability of the LASA noise field, 13 noise samples were used. For every noise sample, power spectra were computed for both the output of seismometer 21 and the output of the multichannel filter system at each subarray. Finally, ratios of the individual spectra to the average spectrum were obtained for each noise sample. At the 0.2- to 0.3-cps microseismic peak, results were consistent for the 13 samples. Subarrays E4, F3, and F4 were significantly quieter sites than the average. It appears that the Porcupine Dome and its associated complex geology significantly attenuated the low-frequency microseismic energy. Subarrays D1, E1, and F1, which are in the northeast sector of LASA, were significantly noisier sites than the average. No explanation for their higher noise levels is known. Variations in the peak power levels were highly correlated over all of the LASA, which implies a common source for most of the energy at 0.2 to 0.3 cps. This observation is consistent with the theory that large storms at sea are the major source of low-frequency microseismic energy. Above approximately 1.5 cps, power levels varied considerably from subarray to subarray as well as from noise sample to noise sample. Thus, most of the energy above 1.5 cps appeared to be nontime stationary and generated in the vicinity of a subarray.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 30, 1967
- Accession Number
- AD0825202
Entities
People
- Terence W. Harley
Organizations
- Texas Instruments