Accession Number : AD0693329

Title :   SPECTRAL ANALYSIS AND STATISTICAL PROPERTIES OF MICROSEISMS AT NORSAR,

Corporate Author : BERGEN UNIV (NORWAY) SEISMOLOGICAL OBSERVATORY

Personal Author(s) : Rygg,Eivind ; Bungum,Hilmar ; Bruland,Leif

Report Date : 01 MAR 1969

Pagination or Media Count : 44

Abstract : Below 0.7 cps the seismic noise recorded by the short period seismometers at NORSAR (Norwegian Seismic Array) is generally dominated by sources in the Atlantic and on the Norwegian coast. When strong low pressure areas are observed outside the coast, the noise has a dominating direction of propagation from the low, and a velocity generally in the range 3-4 km/sec. A low in the Baltic Sea has been found to contribute more to the noise at higher frequencies than the Atlantic sources, its influence extending to lower frequencies as the low moves towards the array. Strong local winds have been found to have little influence in the microseismic range. The noise coherence between sensors is some times much higher in the direction of dominating noise propagation than in other directions. This seems to happen when the noise level is high and when the lows are close to the coast. From the distribution of the sample variances it is assumed that the noise is stationary within half-hour intervals used in the noise analysis. The noise predictability has a maximum during periods with high microseismic activity. (Author)

Descriptors :   (*SEISMOLOGICAL STATIONS, NORWAY), (*MICROSEISMS, POWER SPECTRA), SEISMOMETERS, PHASED ARRAYS, NOISE, HIGH FREQUENCY, DETECTORS, DENSITY, WIND, VELOCITY, STATISTICAL FUNCTIONS

Subject Categories : Seismology
      Seismic Detection and Detectors

Distribution Statement : APPROVED FOR PUBLIC RELEASE